Foundation Science Biology for Class 10 N C Mishra L K Saha Bharati Bhawan useful for NTSE KVPY if missed NSEJS

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Foundation Science

BIOLOGY FOR CLASS 10

N K Mishra, PhD L C Saha, PhD

Foundation Sci Bio Class 10 (iii)

PREFACE

It gives us great pleasure to present this book. It covers, along with our book for class 9, the secondary school biology course of the CBSE. The text has been written in a simple and easy-to-understand style. A lot of information has been presented in tabular and pointwise formats that should aid quick learning, comparison of facts, etc. The diagrams are fairly large, and they have been drawn and labelled as clearly and simply as possible. Wherever possible, photographs have been given. A book for class 10 has special significance because students take the first public examination after this class. Therefore, the content of this book has been prepared to train students for the board examination and beyond. At the end of each chapter points to remember has been given. To help students, the exercises have been divided into three separate groups that have very-short-answer, short-answer and long-answer questions. Apart from these, objective questions, which test a student’s understanding so well, have also been given. Special importance has been given to lab work. A separate chapter, including experiments and short-answer questions for viva voce, has been added. In addition, a separate exercise based on multiple-choice questions has been given. This will prepare students for the written examination based on multiple-choice questions. We would like to thank the editors, proofreaders, artists and typesetter associated with this book. A special word of thanks to the projects manager, who helped in putting all the pieces together. We would like to know whether the book meets the requirement of the students and how it can be improved. We would appreciate feedback and suggestions from teachers and students.

Authors

(iii)

Foundation Sci Bio Class 10 (v)

CONTENTS

1. Nutrition

1

2. Respiration

11

3. Transportation

20

4. Excretion

30

5. Control and Coordination

38

6. Reproduction

50

7. Heredity and Evolution

64

8. Our Environment

82

9. Practicals

94

Question Bank

142

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Nutrition

Nutrition Nutrition Before we learn about the various life processes, we should know the defining characteristics of life. How do we understand what is alive and what is not? We see a variety of things such as mountains, land, buildings, plants, insects, birds, animals, etc., around us. How do we differentiate these things? Some of these, like mountains, land and buildings, are nonliving things, while others like plants, insects, birds and animals are living. What are the basic differences between these? All living things carry out various life processes like taking in food, obtaining energy from food, throwing out wastes, and so on. Living things also move, grow, respond to changes in their external and internal conditions, and produce young ones. All living things (organisms) also have an organized (cellular) structure with different levels of organization. An organized and ordered structure with cells, tissues, organs, organ systems, etc., is an important feature that distinguishes the living from the nonliving. If this organization breaks down, an organism is no longer alive as organization is not only confined to the external appearance, but is present in the internal structure as well. Therefore, living things have to repair and maintain their structures through various processes. Let us learn about some of these processes which help maintain life.

LIVING THINGS AND LIFE PROCESSES You have learnt that living organisms have tissues, which comprise groups of cells with similar structures and functions. A cell is the basic structural and functional unit of any living thing. Each cell is made up of molecules. The molecules exhibit movement during cellular reactions. Such reactions lead to the cellular life activities. There is an absence of such molecular movements in viruses, which remain nonliving until they infect a living organism. Their molecular movement begins when they use the other organism’s cell molecules and organelles for producing their own proteins and replicating themselves. Let us now discuss how living beings grow and how they maintain and repair their structures. The growth of a living organism starts with the division of its cells. When a cell divides, it forms two daughter cells from a single mother cell. The daughter cells divide and redivide to give rise to tissues and organs. Different life processes of an organism, like growth and maintenance, require energy which is obtained from food by a process called nutrition. Different organisms have varied nutritional processes depending on their environment and specific food requirements. Food is broken down into simpler forms by a stepwise oxidizing–reducing process known as respiration. During this process, oxygen is commonly required by organisms to release energy from food for carrying out various life processes. Generally, in multicellular organisms all the cells are not in contact with the environment. The exchange of gases and the uptake of food occur in specialized tissues. So, food and oxygen have to be transported to all parts of the body. For the movement of food and oxygen from one part to another, there is a transportation system. The carrying out of different life processes 1

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involves metabolism (chemical reactions in organisms), which produces harmful waste products that have to be removed from the bodies of living beings. The process of elimination of these waste products of metabolic activity from the body is excretion. In complex organisms a specialized tissue system carries out excretion and a specialized transportation system carries the metabolic waste products to the excretory tissues. The exchange of materials with the environment is accomplished by diffusion in unicellular organisms as the entire surface of the organism remains in contact with the environment. Living things also respond to changes in their environment in a particular manner. They produce new individuals similar to themselves by a process called reproduction. They have a definite life cycle of birth, growth, reproduction and death. From the above discussion it is clear that living things can be easily distinguished from nonliving things as they carry out various life processes such as nutrition, respiration, transportation, excretion, etc. In this chapter we shall discuss the basic concepts of nutrition. Nutrition provides nutrients to the body so that it can obtain energy to carry out the activities required to stay alive. Nutrients are substances that give nourishment, which provides energy to an organism. Cells obtain nutrients from the food taken by the organism. The food taken by the organism is complex, but nutrients are much simpler molecules. The digestive system of an organism breaks down complex food into simpler molecules, so that the cells can take them in and use them for survival, growth and reproduction. Nutrition promotes growth of the body, which involves the formation of new protoplasm. Nutrition meets the energy requirement of the body. Nutrition helps synthesize a variety of substances, like proteins, carbohydrates, lipids, etc., which in turn perform a variety of functions.

MODES OF NUTRITION Plants and animals do not obtain food by the same processes. Plants and some bacteria have the green pigment chlorophyll to help synthesize food, while animals, fungi and other bacteria depend on other organisms for food. Based on this, there are two main modes of nutrition: autotrophic and heterotrophic.

AUTOTROPHIC NUTRITION The term ‘autotroph’ is derived from two Greek words—autos (self) and trophe (nutrition). In autotrophic nutrition, an organism makes its own food from simple raw materials.

Fig.1.1 A summary of nutrition in green plants

Photosynthesis Green plants, which are autotrophic, synthesize food through the process of photosynthesis. Photosynthesis is a process by which green plants, having chlorophyll, synthesize the simple

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sugar (glucose) from the simple raw materials water and carbon dioxide using the energy of sunlight. Oxygen is released in this process. The overall equation of photosynthesis is Sunlight

6CO 2 + 12H 2 O ¾¾¾¾® C 6 H12 O 6 + 6H 2 O + 6O 2 Chlorophyll

The sugar produced is stored in the form of starch in plants. (In animals food is stored in the form of glycogen.) These food reserves provide energy as and when required by the organism. Since autotrophic plants are able to produce food, they are also known as producers.

Site of Photosynthesis Though all green parts of a plant are capable of performing photosynthesis, the leaves are the most suitable organs for this process. The cells of the leaves contain special organelles called chloroplasts, which are the main sites of photosynthesis. These are plastids which contain the light-absorbing green pigment chlorophyll.

Requirements for Photosynthesis Photosynthesis requires chlorophyll, carbon dioxide, water and sunlight. 1. Chlorophyll Chlorophylls are green pigments found in all photosynthetic organisms and are responsible for their green colour. In plants, chlorophyll is mainly found in the leaves. Young stems and fruits may also have chlorophyll. In lower plants like algae, the whole plant is green and takes part in photosynthesis. 2. Carbon dioxide Air contains about 0.03% of carbon dioxide. Terrestrial plants use atmospheric carbon dioxide in photosynthesis. Aquatic plants use the carbon dioxide dissolved in water. Plants obtain carbon dioxide through pores called stomata present on the surfaces of leaves. The opening and closing of these pores are regulated by guard cells, which surround them. Cuticle Upper epidermis Chloroplast

Xylem Phloem

Air spaces Lower epidermis Guard cell CO 2

O2

Stoma

Fig. 1.2 Anatomy of a leaf. Note how plants obtain CO2 through stomata.

3. Water Water is an important raw material for photosynthesis. Plants absorb water from the soil through their root hairs. The water is then transported up to the leaves through the stem. 4. Sunlight Light energy is used in splitting water molecules into hydrogen and oxygen. The splitting of water in the presence of light is called photolysis.

Mechanism of Photosynthesis There are two main stages in the entire process of photosynthesis. The first stage is dependent on light (light reactions). The other stage does not require light (dark reactions). During these two stages, the following events occur. 1. Light energy is first absorbed by chlorophyll molecules found inside the chloroplasts.

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2. The absorbed energy causes splitting of water molecules into hydrogen and oxygen. During this process the light energy gets converted into chemical energy. 3. Finally, carbon dioxide is reduced to carbohydrate (the end product of photosynthesis).

Factors Affecting Photosynthesis Intensity of light, carbon dioxide concentration in the air, temperature and water are the important external factors that influence photosynthesis. Internal factors include chlorophyll content and the accumulation of the products of photosynthesis. 1. Experiment to demonstrate that starch is formed during photosynthesis Pluck a healthy green leaf of a plant which was in the sunlight. Place it in a beaker containing boiling water for about two minutes. Now transfer the leaf to a beaker containing alcohol. Warm it over a water bath for a few minutes. You will observe that the leaf turns white, indicating that the chlorophyll has been removed. Now wash the leaf carefully in water without damaging it. Place the leaf in a dilute solution of iodine. This will turn the leaf bluish black. The changing of the leaf’s colour to bluish black after it has been treated with iodine solution shows that the leaf contains starch. 2. Experiment to demonstrate that carbon dioxide is essential for photosynthesis Get two healthy potted plants of almost the same size and place them in the dark for 24 hours to destarch the leaves. Now place them on glass plates. Cover the plants with separate bell jars. Keep some crystals of potassium hydroxide (KOH) in a Petri dish and place it under one of the jars. Make the set-up airtight by applying Vaseline at the bottom of the bell jars.

Fig. 1.3 Experiment to show that CO2 is essential for photosynthesis

Keep the plants in sunlight for photosynthesis to take place. After 3 to 4 hours pluck a leaf from each plant. Boil the leaves in water and subsequently in alcohol, using a water bath, to remove chlorophyll. Now use a few drops of iodine to test for starch in each leaf. Only one leaf turns blue-black showing the presence of starch. This happens because KOH absorbs the CO2 present inside one bell jar. As a result, the leaves do not get CO2 for photosynthesis. Thus the process of photosynthesis is inhibited and starch is not synthesized. 3. Experiment to show that sunlight is essential for photosynthesis Keep a potted plant in the dark for 24 hours. On one of the leaves, stick black paper strips (one below and one above the leaf) with the help of Sellotape. Now, place this plant in sunlight for a few hours. Pluck the leaf and remove the black strips. Boil this leaf, first in water and then in alcohol, to remove chlorophyll. After washing the leaf with water, keep it in a Petri dish. Add a few drops of iodine solution. The leaf turns blue-black except in the region that had been covered. This region did not receive light and

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hence no starch was formed. The uncovered region received light and starch was formed due to photosynthesis.

Black paper

Does not turn blue-black Blue-black

Fig. 1.4 Experiment to show that sunlight is essential for photosynthesis

Plants take up different nutrients like nitrogen, phosphorus, iron, magnesium, etc., along with water through the root. These nutrients contribute not only to the process of photosynthesis but also to the general development of the plants. For example, nitrogen is used in the synthesis of proteins and other compounds.

HETEROTROPHIC NUTRITION The word ‘heterotroph’ is derived from two Greek words—heteros (other) and trophe (nutrition). Unlike autotrophs, which manufacture their own food, heterotrophic organisms obtain food from other organisms. As heterotrophs depend on other organisms for their food, they are called consumers. All animals and nongreen plants like fungi come under this category. Consumers which consume herbs and other plants are called herbivores, and those which consume animals are called carnivores. After taking complex organic materials as food, heterotrophs break them into simpler molecules with the help of biological catalysts, or enzymes, and utilize them for their own metabolism. Depending upon the mode of living and the mode of intake of food, heterotrophs may be parasitic, saprophytic or holozoic.

Parasitic Parasitic organisms, or parasites, live on or inside other living organisms, called hosts, and obtain their food from them. The host does not get any benefit from the parasite. Different parasites, like Cuscuta (akash-bel), Cassytha (amar-bel), hookworms, tapeworms, leeches, etc., have different modes of feeding, depending upon habit, habitat and modifications. Saprophytic Saprophytic organisms, or saprophytes, derive their food from dead organisms. They secrete enzymes that are released on food material outside their body. These enzymes break down complex food into simple forms. Common examples of saprophytes are fungi (moulds, mushrooms, yeasts) and many bacteria.

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Holozoic In holozoic nutrition complex organic substances are ingested (taken in) without their being degraded or decomposed. After intake, such food is digested by enzymes produced within the organism. Digested food is absorbed into the body and the undigested product is egested (expelled) from the body. This kind of nutrition is found mainly in nonparasitic animals—simple ones like Amoeba and complex ones like human beings.

How Organisms Obtain Nutrition Different organisms obtain food in different ways. Nutrition in unicellular organisms, like Amoeba, involves ingestion by the cell surface, digestion and egestion. Amoeba takes in complex organic matter as food. Amoeba first identifies its food. It then throws out a number of small pseudopodia (projections of cytoplasm, also called false feet). These pseudopodia enclose the food particle and prevent it from escaping. The food enclosed in the cell membrane forms a food vacuole. The complex food is broken down into simpler molecules with the help of digestive enzymes of the organelle called lysosome. The digested food is distributed in the cytoplasm and the undigested food is egested through the cell membrane.

Fig. 1.5 (a) Amoeba sends out pseudopodia to engulf food. (b) Feeding in Paramoecium

In Paramoecium, a unicellular organism with a specific shape, food is ingested through a special opening, the cytostome (cell mouth). Food is brought to this opening by the lashing movement of cilia that cover the entire surface of the cell.

HUMAN DIGESTIVE SYSTEM The alimentary canal and the glands associated with digestion constitute the human digestive system.

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Alimentary Canal The alimentary canal in human beings measures about 8 to 10 metres in length. It extends from the mouth to the anus. It has the following parts. Mouth The mouth consists of the oral cavity, through which food is ingested. It is bounded by lips and cheeks. It contains gums, teeth, a tongue and muscles. The tongue tastes food and moves it into the pharynx. Teeth help in biting, cutting and chewing food. Teeth masticate the food. This makes it easier to swallow food and increases its surface area for various digestive secretions to act on. The four types of teeth are incisors, canines, premolars and molars. Our teeth are covered with a hard protective covering of enamel. The enamel covers the dentine, which is a yellowish substance forming the bulk of the tooth. When we eat sweets, chocolates and ice creams, bacteria act on sugars and produce acids which soften the protective covering. This causes dental caries. Bacterial cells and food particles stick to the teeth and form dental plaque. If the teeth are not brushed properly after meals, bacteria may invade deeper into the teeth. This leads to infection and toothache. The presence of food in the mouth stimulates the three pairs of salivary glands to secrete saliva. Saliva has mucin, which lubricates the mouth and food. Saliva also has salivary amylase, a

digestive enzyme that breaks down starch and glycogen to maltose (a simpler sugar). Pharynx The oral cavity opens into the pharynx. The swallowing mechanism guides the masticated food through the pharynx, into a tube called oesophagus. Oesophagus It is a muscular, tubular part of the alimentary canal. The muscular walls of the oesophagus move in a rhythmic wavelike manner, which carries the food down to the stomach. This muscular movement is called peristalsis. Here also salivary amylase acts on starch and glycogen in the chewed food.

Salivary gland

Mouth

Contraction

Oesophagus Diaphragm

Food

Liver Gall bladder

Stomach

Relaxation

Pancreas Ascending colon Transverse colon Small intestine

Descending colon

Appendix

Rectum (a)

(b)

Fig. 1.6 (a) Alimentary canal and digestive glands of man (b) Food passes down the alimentary canal by peristalsis.

Stomach It is located below the diaphragm (the muscular partition between the chest cavity and abdominal cavity). It is a saclike muscular structure. It serves as a storehouse of food where partial digestion takes place. The stomach has an anterior cardiac and a posterior pyloric part. As in other parts of the alimentary canal, columnar cells line the inner wall of the stomach. The inner lining has

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sunken pits. Each pit constitutes a gastric gland. The cells lining a gastric pit, or gland, are of three kinds: (1) mucous cells (secreting mucus), (2) parietal, or oxyntic, cells (secreting hydrochloric acid) and (3) chief, or zymogen, cells (secreting the inactive enzyme propepsin). The hydrochloric acid in gastric juice converts propepsin to active pepsin and also kills bacteria ingested with food. The mucus protects the stomach lining and glands from being digested by gastric juice. About 3 L of gastric juice is produced per day. Excess secretion of gastric juice, particularly in an empty stomach, erodes the inner lining of the stomach. This erosion causes lesions or round depressions called peptic ulcer in the stomach walls. Digestion of protein begins in the stomach. Pepsin breaks down proteins into peptones. Gastric lipase partially breaks down lipids. Small intestine The small intestine is about 6 metres in length and 2.5 centimetres in thickness. There are three divisions of the small intestine: duodenum, jejunum and ileum. Duodenum is the first part. It begins from the pyloric stomach, and is C-shaped. In the middle of the duodenum two different ducts open through a common aperture. One of the ducts is the common bile duct and the other is the pancreatic duct. Bile, a yellowish green alkaline juice, is poured into the duodenum through the common bile duct. Liver It is the largest gland of the body. It performs many functions. It secretes bile, which helps in digestion. Bile juice produced by the liver is stored in the gall bladder. There are two main functions of bile. 1. It emulsifies fats, by rendering them soluble and breaking them into small globules. In this form, fats are better exposed to the action of fat-hydrolyzing enzymes. (All digestive enzymes catalyze by breaking water molecules, and are hence called hydrolyzing enzymes.) 2. The acidic food (chyme) coming from the stomach becomes alkaline (chyle) when it is mixed with bile. This is important as the intestinal enzymes catalyze the breakdown of food only in an alkaline medium. Pancreas It secretes pancreatic juice, which is carried by the pancreatic duct into the duodenum. Pancreatic juice contains a number of digestive enzymes such as amylase for the splitting of polysaccharides, lipase for the breakdown of fats, and trypsin and chymotrypsin for the breakdown of proteins. These enzymes catalyze the breakdown of their substrates in an alkaline medium. But the catalysis does not completely break all the substrates into their simplest units. Jejunum is the middle part of the small intestine. It is found only in man. Ileum is the last and main part of the small intestine. The major part of digestion and absorption takes place here.

Intestinal glands The complete digestion of the remaining food material takes place in the ileum. There are numerous small glands in the walls of the small intestine. These glands secrete intestinal juice. The digestive enzymes in the intestinal juice break small peptides into amino acids, disaccharides into monosaccharides, lipids into fatty acids and glycerol, and nucleic acids into nucleotides. Large intestine The ileum passes into the large intestine. The large intestine can be divided into two parts: anterior (colon) and posterior (rectum). At the junction of ileum and colon, there is a blind (one end closed) outgrowth called caecum. The caecum ends in the vermiform appendix (Latin vermis = worm; vermiform = worm-shaped). In man, the vermiform appendix has outlived its usefulness; it is a vestigial organ. It is an 8-cm-long blind tube, which sometimes becomes a source of trouble. The colon has an ascending part, a transverse part and a descending part. The last part, or the descending part, opens into the rectum. The terminal part of the rectum is called anal canal. It opens through the anus, guarded by the sphincter muscles. The large intestine allows the passage of residual food mass (faecal matter), which is egested through the anus. As the residue of the food mass passes along the large intestine, a considerable amount of water contained in the residue is absorbed into the blood through the intestinal walls. The specialized longitudinal muscles present in the colon wall regulate the passage of the faecal matter along the colon.

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Take two clean test tubes. Pour 1 mL starch solution (1%) in each of them. Add 1 mL saliva in one test tube only and keep both the test tubes in a test tube holder undisturbed for half an hour. Now add a few drops of iodine solution in both the test tubes. You will observe that the saliva-containing test tube shows no blue-black colour, while the other test tube does. What does it indicate? It shows that saliva contains some enzyme which has converted starch into some simpler compounds. In fact, salivary amylase present in saliva breaks down starch into maltose.

Absorption of Digested Food Absorption of completely digested food takes place in the ileum. The wall of the ileum has fingerlike projections called villi that increase the surface area for absorption of digested food. The villi are richly supplied with blood vessels to carry the absorbed food (Figure 1.7). The absorbed food is then brought into the blood capillaries. From the blood capillaries, absorbed materials are transported by veins to the liver and then to the heart for distribution to different parts of the body.

Fig. 1.7 Villi of small intestine

Assimilation of Digested Food Intake of digested food by cells of the body is called assimilation. Digested food is utilized by the body in many ways. It is used to obtain energy through the process of respiration. Excess monosaccharides are stored as glycogen. Amino acids are used in the synthesis of proteins. The glycerol and fatty acids either provide energy or get reconverted into fats. These fats are accumulated in different organs below the skin. The absorbed food is also utilized for the formation of new cells and tissues, leading to the growth and development of the body.

• POINTS TO REMEMBER • ·

Living beings can be distinguished from nonliving things due to their organized structure and life processes, like nutrition, respiration, transportation, excretion and reproduction.

·

Nutrition is the process of providing nutrients to the body cells. In this, food is taken in by the organism, digested and assimilated. The assimilated food is utilized by the cells for the production of energy and the synthesis of proteins, etc.

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Nutrition may be autotrophic or heterotrophic. All green plants are autotrophs. Nongreen plants and animals depend on autotrophs for their food and are thus called heterotrophs.

·

Chlorophyll pigments in green plants are unique in their property of trapping solar energy and converting it into chemical energy. Photosynthesis occurs in the chloroplasts. It requires sunlight, chlorophyll, water and carbon dioxide. It produces glucose and liberates oxygen.

·

·

·

·

·

In photosynthesis, solar energy is absorbed by chlorophyll. The absorbed energy causes splitting of water molecule. O2 is liberated as by-product. There are various forms of the heterotrophic mode of nutrition such as saprophytic (feeding on dead and decaying organic matter), parasitic (depending upon a living host), and holozoic (involving (a) ingestion, (b) digestion, (c) absorption and (d) egestion). Amoeba ingests food by the infolding of its cell membrane around the food. After digestion and assimilation, it egests the undigested material. Human digestion begins in the mouth. In the stomach, digestion of protein occurs in an acidic medium. In the duodenum, the food is turned alkaline by the bile juice and digestion occurs with the help of enzymes from the pancreas. In the ileum, digestion occurs with the help of intestinal juice produced by the intestinal glands. Absorption of digested food occurs in the small intestine with the help of villi. The large intestine helps in water absorption.

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• EXERCISES • A. Very-Short-Answer Questions

5. Describe the process of nutrition in Amoeba. 6. Define the terms ‘nutrition’ and ‘nutrients’. List two differences between holozoic nutrition and saprophytic nutrition. Give two examples of each of [CBSE] these two types of nutrition.

1. Why is diffusion sufficient for transporting food and oxygen in unicellular organisms? 2. How can we distinguish the living from the nonliving things? 3. Name the different modes of nutrition.

D. Objective Questions

4. Name the requirements for photosynthesis.

I. Pick the correct option.

5. What are the two stages in photosynthesis?

1. Which of the following options describes the characteristics of a living being? (a) Nutrition (b) Respiration (c) Excretion (d) All of these

6. How do autotrophs obtain CO2 and N2 to make their food? [CBSE] 7. What is the action of saliva on starch?

2. Which of these is not required for photosynthesis? (a) Sunlight (b) Carbon dioxide (c) Oxygen (d) Water

8. What is peristalsis? 9. Name the three parts of the small intestine.

[CBSE]

3. Amoeba captures food with the help of (a) teeth (b) cilia (c) pseudopodia (d) tentacles

B. Short-Answer Questions 1. Define nutrition. 2. Differentiate between producers and consumers with examples.

4. The largest gland associated with the human alimentary canal is (a) stomach (b) liver (c) pancreas (d) small intestine

3. Why are leaves suitable for photosynthesis? 4. Differentiate between the following. (a) Saprophytic and holozoic digestion (b) Herbivore and carnivore

5. The mode of nutrition in green plants is (a) autotrophic (b) holozoic (c) heterotrophic (d) saprophytic

5. What do the gastric glands secrete and how do these help in digestion?

6. In humans the process of digestion begins in the (a) oesophagus (b) mouth (c) stomach (d) pharynx

6. What is the role of hydrochloric acid in our stomach?

II. Fill in the blanks.

7. Mention any two ways in which digested food is utilized by the body.

1. The process by which green plants synthesize their food is called _____.

C. Long-Answer Questions 1. Describe the human digestive system.

2. Organisms that derive their food from decaying matter are called _____.

2. Mention the major glands associated with the alimentary canal of man, and their functions.

3. The mode of nutrition in Amoeba is _____. 4. The glands which produce salivary amylase are called _____.

3. How will you test for the presence of starch in a leaf?

5. The wall of the ileum has fingerlike projections called _____ , which have absorptive cells.

4. Give an account of the process of photosynthesis.

• ANSWERS • Objective Questions 1. (d) 6. (b)

2. (c)

3. (c)

4. (b)

5. (a)

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Respiration

All living organisms require energy to carry out life processes. This energy comes from food. However, processes carried out in cells cannot use the energy locked in stored food, fats, etc., directly. Cellular processes get usable energy from a process called respiration. Respiration commonly involves the use of oxygen to break down carbohydrates and other organic molecules, giving usable energy, carbon dioxide and water in the process. Respiration All organisms breathe—a process in which they take in oxygen and give off carbon dioxide. This is called external respiration. Internal respiration, or cellular respiration, takes place inside every living cell. In this process, carbohydrates and other organic molecules are broken down in successive steps to produce energy, which is used to make a compound called adenosine triphosphate (ATP). Cellular processes get energy from ATP. ATP is often called the ‘energy currency’ of the cell. The amount of ATP in a cell indicates how energy-rich it is. Where does this energy come from? During photosynthesis, carbon dioxide and water combine with the help of the energy from the sun to form ca rbohydrates. Energy gets stored in the bonds of the carbohydrates. In respiration, these bonds are broken to release energy and give back carbon dioxide and water. This energy then gets stored in the bonds of ATP. These bonds get easily broken to release energy when required by the cells. We can study cellular respiration by taking the example of the complete oxidation of glucose. This molecule is oxidized and broken down gradually in two distinct stages. The first stage is called glycolysis, which involves anaerobic respiration. This takes place in the cytoplasm of the cell. The second stage involves aerobic respiration, which takes place inside the mitochondria of the cell. The overall reaction can be represented as follows. C 6 H12 O 6 + 6O 2 ¾® 6CO 2 + 6H 2 O + Energy (glucose)

Anaerobic Respiration Partial oxidation of food in the absence of oxygen, resulting in the release of some amount of energy, is called anaerobic respiration. Anaerobic means without oxygen or in the absence of oxygen, while aerobic means with oxygen or in the presence of oxygen. Glucose has six carbon atoms joined to each other by covalent bonds. Hydrogen and oxygen atoms are also attached to these carbon atoms. In anaerobic respiration of glucose, some hydrogen atoms are removed from it, resulting in its oxidation. (The addition of oxygen or the removal of hydrogen is oxidation.) At the end of a series of reactions, glucose gets converted into two molecules of pyruvate, which contains three carbon atoms. These reactions also produce two molecules of ATP. The oxidation of glucose in a series of reactions leading to the formation of pyruvate is called glycolysis. 11

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Glycolysis means ‘splitting of sugar’. It takes place in all organisms, in the cytoplasm of the cell. It is the first stage of respiration—both aerobic and anaerobic. After glycolysis, its product (pyruvate) gets converted into different compounds depending on whether further reactions take place in the presence or absence of oxygen. Glycolysis is the last energy-producing stage in case oxygen is absent or in low supply, and in cells that lack mitochondria. After glycolysis, further anaerobic reactions produce different products like lactic acid or ethanol (ethyl alcohol) in different situations. This step completes the anaerobic respiration of glucose. Anaerobic respiration resulting in the formation of these products is also called fermentation. Examples of lactic acid fermentation and alcohol fermentation are given below. In a low supply of oxygen, yeast converts pyruvate to ethanol and carbon dioxide. Certain bacteria (which lack mitochondria) convert pyruvate to lactic acid. When our muscles are overworked, blood is unable to supply oxygen fast enough for producing energy through aerobic means. In this low-oxygen condition pyruvate gets converted to lactic acid. Accumulation of excess lactic acid in the muscles causes pain.

Fig. 2.1 Different ways in which glucose gets oxidized

In aerobic respiration, a different path is followed after glycolysis. In the presence of oxygen, in cells that have mitochondria, pyruvate is oxidized further in a number of steps to produce more energy, carbon dioxide and water.

Aerobic Respiration The complete oxidation of food yielding carbon dioxide, water and energy in the presence of oxygen is called aerobic respiration. Aerobic respiration takes place inside the mitochondria. After glycolysis, pyruvate enters the mitochondria and is oxidized in a series of reactions. The products of these reactions include ATP, carbon dioxide and water. The number of molecules of ATP formed in aerobic respiration is 38. Hence the energy made available is much greater than in the case of anaerobic respiration. Inside the mitochondria, when an inorganic phosphate group (PO 34 - , represented here as Pi ) gets attached to a compound called ADP (adenosine diphosphate), a molecule of ATP (adenosine triphosphate) is formed. ADP + Pi ¾® ATP The bond holding the last (terminal) phosphate group is easily broken when ATP reacts with water. In the process, energy is produced. This energy is used to drive cellular processes that are endothermic (i.e., processes that absorb energy). Processes like protein synthesis, contraction of muscles, etc., get energy from ATP.

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Table 2.1 Differences between aerobic and anaerobic respiration Aerobic respiration

Anaerobic respiration

1. Aerobic respiration takes place in the presence of oxygen.

1. Anaerobic respiration takes place in the absence of oxygen.

2. The first step in this process (glycolysis) takes place in the cytoplasm, while the second step takes place in the mitochondria.

2. The complete process takes place in the cytoplasm.

3. Glucose is completely oxidized into carbon dioxide, water and energy.

3. Glucose is incompletely oxidized either into carbon dioxide, ethyl alcohol and energy (as in yeast) or into lactic acid and energy (as in muscle cells).

4. 38 molecules of ATP are produced by the complete oxidation of one gram-mole of glucose.

4. Only 2 molecules of ATP are formed in this process.

1. Take two clean test tubes. Pour freshly prepared limewater in each of them. Keep the test tubes in a test-tube stand. Use a syringe to inject air into the limewater in one test tube. Take the syringe out of limewater. Pull up the piston to fill it with air and inject more air into the limewater. Repeat the process till the limewater turns milky. Note the time taken in this process. Now, use a glass tube to blow air into the limewater in the other test tube. You will find that the limewater in the second test tube turns milky in lesser time. This is because the air we breathe out has more CO2 than does atmospheric air.

Syringe

Glass tube

Test tube Limewater turns milky fast

CO 2 in air

CO 2 in exhaled air (a)

(b)

Fig. 2.2 (a) Injecting air with a syringe (b) Blowing air by mouth

2. Take some fruit juice in a clean conical flask. Add some yeast to it. Pass a bent glass tube through a cork, and fit the cork into the mouth of the conical flask. Place the other end of the glass tube inside a test tube containing freshly prepared limewater. The limewater turns milky. This shows that carbon dioxide is liberated during fermentation by the yeast cells.

Glass tube Cork

Fruit juice + yeast

Limewater turns milky

Fig. 2.3 Fermentation produces carbon dioxide.

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Exchange of Gases in Plants In plants, oxygen and carbon dioxide diffuse through the stomata and the intercellular spaces of the leaves, and the lenticels of the bark. In woody plants, the stem is covered with bark. Lenticels are small openings in the pits of the bark. The exchange of gases takes place through the lenticels also, apart from the exchange through the openings in the leaves.

Fig. 2.4 Stomata

The direction of exchange of gases between a plant and its surroundings depends upon the time of the day and the usage of the gases by the plant. Plants respire throughout the day, while photosynthesis takes place only in the presence of sunlight. In daytime, carbon dioxide produced in respiration by the plants is used by them in photosynthesis. So, carbon dioxide is not released into the environment. In fact, plants take in additional carbon dioxide from the air for photosynthesis. Out of the oxygen produced in photosynthesis, some amount is consumed by the plants in respiration. The rest is released into the air through the stomata. At night, when there is no photosynthesis, no oxygen is released. Also, the carbon dioxide produced in respiration is not used by the plants. So, it is released in the air. That is why it is advised not to sleep under trees at night. In summary we can say that in daytime, on the whole, the plant releases oxygen and takes in carbon dioxide. And at night the plant releases carbon dioxide and takes in oxygen. Different parts of the plant respire independently. For example, the root takes in oxygen present in the soil by the process of diffusion. Oxygen diffuses into the root hairs and passes into the other cells of the root. And carbon dioxide released by the root cells diffuses into the soil. Since the root is involved in the exchange of gases, if the root of a land plant remains waterlogged for long, the plant dies. In certain respects, respiration in plants is different from that in animals. For example, plants produce some of the oxygen used by them for respiration. In plants, respiration occurs at a much slower rate than in animals. Also, there is little transport of gases from one part of the plant to another, unlike in animals.

Exchange of Gases in Animals In small organisms (e.g., Amoeba, Paramoecium) the exchange of gases occurs through the general surface of the body or the cell membrane. However, larger animals (e.g., birds, mammals) have a much greater requirement of energy. Hence they need much more oxygen than can be met through diffusion across the general surface of the body. Therefore, they have special respiratory organs that have a greatly enlarged surface area through which oxygen can diffuse. For example, the human lungs have millions of air sacs whose surface area is many times that of the body. These air sacs are involved in the exchange of gases. In animals, there are three types of respiratory organs—tracheae, gills and lungs. Insects have a fine system of air tubes reaching all parts of the body. Such a tube is called trachea. Oxygen reaches the tissues through the tracheae. Gills are respiratory organs found in aquatic

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animals. You may have seen the gills of a fish. Reptiles, birds and mammals have lungs for the exchange of gases.

Fig. 2.5 Exchange of gases in some organisms

Aquatic animals have to use the oxygen dissolved in water. Hence, they have some special organs such as gills to absorb it. In fish, as water enters the mouth, it passes through the chambers where the gills are present. The exchange of gases takes place through the gills. The blood vessels in the gills absorb the oxygen dissolved in water. Terrestrial animals use the abundant oxygen of the atmosphere for respiration. Since the solubility of oxygen in water is low, there is not much oxygen available for aquatic organisms. Therefore, to make up for the low availability of oxygen, the rate of breathing in aquatic organisms is much higher than that in terrestrial organisms.

Fig. 2.6 Respiration in fish

Observe fish kept in an aquarium. You will see that they open and close their mouth and operculum (gill covering) in quick succession. The rate at which they do this is higher than the rate at which we breathe. The higher rate of breathing is necessary to take in the required amount of oxygen from the limited amount dissolved in the water.

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THE HUMAN RESPIRATORY SYSTEM The human respiratory system consists of a pair of lungs and a series of air passages leading to the lungs. The entire respiratory tract (passage) consists of the nose, pharynx, larynx, trachea, bronchi, and bronchioles.

Fig. 2.7 Human respiratory system

Air enters the nose through the nostrils. When air passes through the nose, it is warmed, moistened and filtered. The hairs present in the nose filter out particles in the incoming air. The air is moistened by the mucus present in the nose, and it is warmed by the blood flowing through the capillaries in the nose. The respiratory tract from the nose to the bronchioles is lined by mucous membranes and cilia. The mucus and cilia act as additional filters. Behind the nose lies the pharynx (throat). There are two passages here—one for food and the other for air. The air passes from the pharynx to the larynx, or the voice box. The opening leading to the larynx is called glottis. It is protected by a lid called epiglottis, which prevents food from entering the passage to the lungs. From the larynx the air goes to the trachea, or the windpipe. The trachea is about 11 cm long. It is guarded by 16–20 C-shaped cartilage rings, which prevent the trachea from collapsing. The trachea divides into two tubes called bronchi. Each bronchus divides and branches out in the form of thinner tubes called bronchioles. The bronchioles enter the lungs and divide further into finer branches called alveolar ducts. These open into extremely thin-walled, grape-shaped air sacs called alveoli. Each alveolus is covered by a web of blood capillaries. The lungs are a pair of spongy organs lying in the chest cavity formed by the ribs. The actual exchange of gases between the air and the body takes place in the capillary-covered alveoli inside the lungs. Here, oxygen from the air in the alveoli goes into the blood, and the carbon dioxide in the blood goes out. The oxygen binds to the haemoglobin molecules present in the red blood corpuscles and is taken to different parts of the body.

Fig. 2.8 Alveoli

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The total surface area through which the exchange of gases can take place increases because of the millions of alveoli in the lungs. Their total surface area can be about a hundred times that of the body. The large surface area allows sufficient oxygen intake needed for releasing the large amount of energy required by us.

Mechanism of Breathing There are two main steps in breathing: inspiration and expiration. Inspiration Inspiration (inhalation) is the process of breathing in, by which air is brought into the lungs. Inspiration involves the following steps. The muscles attached to the ribs on their outer side contract. This causes the ribs to be pulled out, expanding the chest cavity. The muscle wall between the chest cavity and the abdominal cavity, called diaphragm, contracts and moves downwards to further expand the chest cavity. The abdominal muscles contract. The expansion of the chest cavity creates a partial vacuum in the chest cavity. This sucks in air into the lungs, and fills the expanded alveoli. Expiration After the exchange of gases in the lungs, the air has to be expelled. Expulsion of the air from the lungs is called expiration. In this process, muscles attached to the ribs on their inner side contract, and the diaphragm and the abdominal muscles relax. This leads to a decrease in the volume of the chest cavity, which increases the pressure on the lungs. The air in the lungs is pushed out and it passes out through the nose. When we breathe out, not all of the air in the lungs gets expelled. Some of it remains in the lungs. This keeps the lungs from collapsing and allows more time for the exchange of gases.

Transport of Gases In very small organisms, there is no need to have a separate transportation system for gases because all its cells are involved directly in the exchange of gases by diffusion. However, a large multicellular organism needs a mechanism for the transport of gases for its different organs and tissues. Human beings also have a system for transportation of gases. Oxygen is carried by haemoglobin of the red blood cells. Haemoglobin has a great affinity for oxygen—each haemoglobin molecule binds to four molecules of oxygen. The oxygen ‘picked up’ by haemoglobin gets transported with the blood to various tissues. Carbon dioxide is more soluble in water than oxygen. So, some of it is transported in the dissolved form in our blood. Some carbon dioxide is also transported by haemoglobin. Not all of the carbon dioxide formed is expelled from the body. Some of it reacts with water to form compounds useful for life processes.

Fig. 2.9 The overall process of respiration

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• POINTS TO REMEMBER • ·

·

·

Respiration commonly involves the use of oxygen to break down carbohydrates and other organic molecules, giving usable energy, carbon dioxide and water in the process. All organisms take in oxygen from the environment and give off carbon dioxide. This process is external respiration. Cellular respiration takes place inside the living cell. In this process, carbohydrates and other organic molecules are broken down in successive steps to produce ATP, which provides energy for cellular processes. Partial oxidation of food in the absence of oxygen, resulting in the release of some amount of energy, is called anaerobic respiration.

·

The oxidation of glucose in a series of reactions leading to the formation of pyruvate is called glycolysis.

·

The complete oxidation of food yielding carbon dioxide, water and energy in the presence of oxygen is called aerobic respiration.

·

Respiration involves the exchange of gases. In plants, the gases diffuse through the stomata, lenticels, and intercellular spaces. In animals, the organs that help in the exchange of gases include gills, tracheae (air tubes) and lungs.

• EXERCISES • A. Very-Short-Answer Questions 1. Which molecule supplies usable energy for cellular processes? 2. Name two end products of anaerobic respiration. 3. In which part of the cell does aerobic respiration take place? 4. Why do higher animals have special respiratory organs with large surface area? 5. Name the two steps in breathing.

8. What is the function of the epiglottis in man? Draw a labelled diagram showing the human respiratory system. [CBSE] 9. How does the total surface area through which the exchange of gases can take place in the lungs become large? What is its advantage? C. Long-Answer Questions 1. What is glycolysis?

6. Define aerobic respiration.

2. Distinguish between anaerobic respiration.

7. What are the ways in which glucose is oxidized in organisms?

3. Explain how the direction of exchange of gases in plants changes with the time of the day.

8. In which type of respiration is more energy released?

4. Describe how the exchange of gases takes place in the lungs.

9. What happens to the air as it passes through the nose?

B. Short-Answer Questions 1. Differentiate between external and internal (or cellular) respiration. 2. What are the steps involved in the formation of lactic acid from glucose? 3. Why is the rate of breathing faster in aquatic organisms than in terrestrial organisms? 4. Differentiate between respiration in plants and animals. 5. In what forms are oxygen and carbon dioxide transported in the blood? 6. How are oxygen and carbon dioxide transported in human beings? How are lungs designed to [CBSE] maximise the area for exchange of gases? 7. Give reasons for the following. [CBSE] (a) The glottis is guarded by the epiglottis. (b) The alveoli in lungs are covered with blood capillaries. (c) The wall of trachea is supported by cartilage rings.

aerobic

respiration

and

D. Objective Questions

Pick the correct option. 1. The energy-rich compound produced during respiration is (a) ATP (b) ADP (c) pyruvate (d) AMP 2. The final product of glycolysis is (a) lactic acid (b) glucose (c) ethanol (d) pyruvate 3. The series of reactions resulting in the oxidation of glucose leading to the formation of pyruvate is called (a) fermentation (b) glycolysis (c) aerobic respiration (d) anaerobic respiration 4. The common stage between aerobic and anaerobic respiration is called (a) oxidation (b) reduction (c) photosynthesis (d) glycolysis 5. Aerobic respiration takes place in the (a) nucleus (b) cytoplasm (c) mitochondria (d) vacuole

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6. Which of the following acids is the end product of fermentation? (a) Hydrochloric acid (b) Lactic acid (c) Pyruvic acid

(a) stomata (b) gills (c) lungs (d) alveoli 8. Gaseous exchange in fish takes place through the (a) trachea (b) lungs (c) gills (d) alveoli

(d) Citric acid

7. Gaseous exchange in plants takes place through the

• ANSWERS • Objective Questions 1. (a) 6. (b)

2. (d) 7. (a)

3. (b) 8. (c)

4. (d)

5. (c)

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Transportation

Transportation In order to carry out various life processes like nutrition and respiration, organisms require food and oxygen. It is also necessary for the organisms to get rid of the waste products of cellular processes. Food, oxygen and waste products need to be carried from one part of the body to another. In unicellular organisms and many simple multicellular organisms, materials are transported by osmosis and diffusion. In higher organisms this is done by a specialized transport system called the vascular system.

TRANSPORTATION IN PLANTS Plants take in some compounds like carbon dioxide through their leaves. They absorb some other materials such as compounds of nitrogen, phosphorus, etc., from the soil through their roots. If the distance between the roots and leaves is very small, food and other materials can be transported by diffusion. But the distances between different plant parts are often quite large, as in tall trees. Therefore, most plants need a proper transport system to carry materials from one part to another. Plants do not move much and have many dead cells in their tissues. Therefore, they do not need much energy. So, they have transport systems slower than those of animals. In plants, the transport system consists of tubelike passages made up of vascular tissue. There are two types of vascular tissues in plants—xylem and phloem. The vascular system extends from the roots through the stem and continues up to the leaves. In the leaves it is clearly seen as a pattern of veins. Water and minerals are transported from the roots upwards through the xylem tubes. Phloem transports synthesized food from the leaves to the rest of the plant body. The transport of water, nutrients and other substances from one part of a plant to another is called translocation. The medium of transport in plants is water.

Transport of Water and Minerals The xylem tissue transports water and minerals. It consists of interconnected vessels and tracheids organized into continuous conducting tubes stretching from the roots to the leaves. These tubes carry water and minerals to all parts of the plant. Plants absorb water from the soil through the root and transport it to the stem, leaves and flowers. Roots have root hairs that are unicellular, thin-walled outgrowths of the epiblema (skin of the root). The root hairs are in close contact with the thin film of water surrounding the soil particles. There are mineral salts such as nitrates, chlorides, sulphates, phosphates, etc., dissolved in this water. Water is absorbed by osmosis, while the minerals are absorbed as ions by active transport (transport against the law of diffusion, by spending cellular energy). The cell membrane has transport proteins that allow the ions to cross the membrane. The ions then move upward through the xylem, to the leaves and other aerial parts of the plant. 20

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Ascent of Sap The transport of water and dissolved mineral salts from the roots to the leaves is known as ascent of sap. The cell wall of each root hair is permeable to water and minerals, but its cell membrane and the membrane around the vacuole are semipermeable membranes. The root hair cells take up mineral ions by active transport. This creates a concentration difference of these ions between the root and the soil. Now, the soil solution has higher water content than the cell sap of the root hair. Hence, water from the soil diffuses into the root hair. The root hair cells now become turgid, while the adjacent cells of the cortex have lower water content. This results in the diffusion of water from the root hairs into the cortical cells (Figure 3.1). After passing through the cortical cells by osmosis the water reaches the endodermis (tissue separating the cortex from the vascular tissues). The endodermis forces water into the xylem tubes through passage cells.

Fig. 3.1 Absorption of water through root hair

The pressure with which water is pushed into the xylem tubes of the root is called root pressure. The water moving upwards forms a column, which is maintained up to a certain height due to root pressure. In tall trees, this type of absorption plays a minor role in transporting water. This process is slow, and it cannot make up for the water lost by transpiration (the evaporation of water from the leaves). Transpiration is rapid during the day. The loss of water due to transpiration creates a suction force that pulls water up through the xylem vessels. This transpiration pull serves as the main force that transports water through the xylem. Root pressure helps in the transport of water at night.

Fig. 3.2 Relationship between transpiration and

absorption. Water absorbed by the root passes up to the leaf through the xylem of the stem.

Fig. 3.3 Plants lose excess water by transpiration.

Take a healthy potted plant and enclose some of its leaves in a plastic sheet. Then keep the plant in bright sunlight. After some time, you will observe droplets of water on the inner surface of the plastic sheet. This water was lost through the stomata on the leaves as a result of transpiration. The rate of transpiration is high if the atmosphere is warm and dry.

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Transport of Food and Other Substances The food manufactured in the leaves is translocated upwards, downwards and laterally to all parts of the plant through the phloem. The phloem also conducts some other substances such as amino acids. The conducting cells of the phloem are cylindrical cells called sieve tubes, which have sievelike partitions at both ends. These partitions are called sieve plates. A continuous column from the leaves to other parts of the plant is formed by the arrangement of sieve tubes one above the other. Besides sieve tubes, the phloem also has companion cells and phloem parenchyma. Sucrose is the main form of carbohydrate that is translocated in plants. Its translocation into the phloem tissue occurs with the expenditure of energy. When sucrose is synthesized in the leaf cells, the osmotic pressure of the cells increases. As a result, water from the surrounding cells is forced to flow into the leaf cells by osmosis. This causes sucrose to be translocated from the point of its synthesis to the receiving end in the form of a solution. This process is dependent on the requirement of the plant. For example, in the flowering season, when vegetative activity is more at the apex of the plant, sugar in the leaves will be readily consumed. This is the reason for the translocation of sugar to the buds from the storage regions (root, stem, etc.) during spring. Excess food is transported to the storage regions when the vegetative activity of the plant is reduced. Table 3.1 Differences between xylem and phloem 1.

Xylem cells are dead, whereas phloem cells are alive.

2.

Xylem carries mainly water and minerals, while phloem carries organic compounds such as sugar and amino acids.

3.

The flow of liquid in xylem is upward only, whereas the flow of liquid in phloem is in all directions. Fig. 3.4 (a) Xylem vessels (b) Phloem tubes (in

longitudinal section)

TRANSPORTATION IN ANIMALS In very simple animals, materials are transported through diffusion. In complex animals, there is a special transport system to carry oxygen, carbon dioxide, nutrients, waste products, food and various other substances from one part of the body to the other. This transport system, also called the circulatory system, comprises a blood vascular system and a lymphatic system. The blood vascular system has three components—blood, blood vessels and the heart. The lymphatic system includes lymph, lymph vessels and lymph nodes.

Blood—a Fluid Transport Medium Blood is a liquid connective tissue having two main components—plasma and blood corpuscles. Plasma is the liquid part of the blood. It is made up of water with various substances dissolved in it. These include proteins, salts, glucose, nitrogenous compounds, and so on. In many invertebrates, plasma contains the respiratory pigment. Corpuscles are cells floating in the plasma. Red blood cells, a type of corpuscle in vertebrates, contain a red-coloured respiratory pigment called haemoglobin.

Heart—a Pumping Organ The heart is a muscular pumping organ. It pumps blood that comes to it from other parts of the body through the circulatory system. It pumps deoxygenated blood to the lungs for oxygenation, and oxygenated blood to all parts of the body.

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Control of the heart The invertebrate heart is generally fully controlled by the nervous system. The vertebrate heart is controlled by a pacemaker system made up of specialized cardiac muscles. Chambers in the heart The heart is divided into chambers in order to prevent the mixing of oxygenated blood with deoxygenated blood. A complete vertical partition of the heart into left and right chambers ensures a complete separation of oxygenated and deoxygenated blood. This type of partition is seen in animals having a double circulation system, with two circuits. These animals (e.g., mammals, birds and crocodiles) have lungs. In one circuit blood flows between the heart and the lungs, and in the second circuit it flows between the heart and the body. The heart has four chambers—two atria (often also called auricles) and two ventricles. Such a heart is called ‘double’ heart. This type of complete separation into chambers provides an ample supply of oxygen to all parts of the body. These animals are quite active, so they have a high rate of respiration and require an efficient supply of oxygen. Birds and mammals, being warm-blooded, need to spend energy to regulate their body temperature. This also requires oxygen. Some vertebrates do not use energy for temperature regulation. Their temperature fluctuates with that of the environment and we call them cold-blooded. In these animals (except crocodiles) there is some mixing of oxygenated and deoxygenated blood in the heart. This does not harm the animals as their energy demands are not very high. In amphibians the heart is three-chambered, having two atria and a single ventricle. Such a heart is called transitional heart. In most reptiles there are two atria and an incompletely divided ventricle. Fish have a single circulation system. Their heart is two-chambered, having one atrium and one ventricle. Such a heart is called ‘single’ heart. The fish heart receives and pumps only impure blood. The impure blood goes to the gills for oxygenation, and from there it goes to different parts of the body. The impure blood returns to the heart for being pumped out to the gills. Therefore, the fish heart is also called venous heart.

Blood Vessels In vertebrates the blood vessels are arteries, veins and capillaries. Arteries are more muscular, while veins are more elastic. Capillaries are made up of a single layer of squamous epithelium. In invertebrates the blood vessels are not properly distinguished as arteries and veins.

CIRCULATORY SYSTEM IN MAN Blood Blood, as you know, is a liquid connective tissue that circulates in a closed system of blood vessels. An adult man has about five to six litres of blood, while a woman, on an average, has about one litre less. Our blood consists of (i) solid elements—which include red blood corpuscles (RBCs), white blood corpuscles (WBCs), and blood platelets, and (ii) liquid element—the plasma. The corpuscles comprise about 45% and the plasma about 55% of the volume of blood. Plasma Plasma is a straw-coloured liquid in which the RBCs, WBCs and platelets float. It contains mainly water, in which are dissolved various substances such as plasma proteins, food substances (amino acids, glucose, fats), nitrogenous compounds and ions of sodium, potassium, calcium, magnesium and phosphorus. Blood corpuscles Blood is red in colour due to the presence of RBCs. The RBCs contain the red-coloured respiratory pigment haemoglobin. This iron–protein compound transports oxygen from the lungs to the tissues. RBCs also transport carbon dioxide. WBCs protect the body from infection. Platelets help in the clotting of blood.

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Visit a diagnostic centre. Give your blood sample. Get it checked for the level of haemoglobin. The normal range of haemoglobin in humans is 120–180 g/L, or 12–18 g/dL, of blood. Check your blood report to see if your haemoglobin level falls in this range. But haemoglobin levels also depend on age, sex and ethnic values of a place. For example, females have a lower normal value of haemoglobin level than males. A below-normal level of haemoglobin may indicate anaemia due to a number of possible causes. Low haemoglobin level could be from actual loss of blood from haemorrhage, vitamin deficiencies, lack of iron in the diet or a disease. This indicates that the person’s cells are not getting enough oxygen for energy production. Such anaemic persons always feel tired and weak. You can even obtain the normal range of haemoglobin level in animals such as cows, buffaloes, goats, etc., by visiting a veterinary clinic. This value is lower in these animals than in humans. The normal haemoglobin level in cows lies in the range of (5.9 ± 1.54) g/dL of blood.

Blood clotting by platelets You must have noticed that after a cut the skin bleeds for a while, and then the blood thickens to form a clot. This process takes place as a result of a series of reactions in the blood. These reactions are started by the release of an enzyme by the circulating platelets. The clot, which forms at the point of the wound, is a microscopic network of insoluble fibrous protein. It minimizes the loss of blood. If blood is lost, it leads to a loss of pressure by the pumping heart. Functions of blood 1. Transport of respiratory gases Blood carries oxygen from the lungs to the tissues. It also carries carbon dioxide from the tissues to the lungs. 2. Transport of nutrients Nutrients absorbed in the small intestine enter the blood capillaries. Blood carries these nutrients and distributes them to all parts of the body. 3. Transport of waste products Waste products of the body, such as urea, uric acid, etc., are carried by blood to the excretory organs. 4. Regulation of water content of cells Blood regulates the water content of the cells. When the water content in cells increases, blood takes up the excess amount of cellular water. Blood provides water to cells when they need it. 5. Regulation of body temperature Increased body temperature resulting from the excess respiration of a particular tissue is equalized by circulation of blood. 6. Defence against infection Blood protects the body against infection. 7. Prevention of bleeding Clotting blood prevents excess bleeding.

of

Blood Vessels Three types of blood vessels, namely, arteries, veins and capillaries, are involved in blood circulation. They are all connected to form one continuous closed system. Arteries The arteries are wide, elastic and thick-walled vessels as they carry blood

Fig. 3.5 Route of blood circulation

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away from the heart to the limbs and organs of the body. They have thick, elastic walls to withstand the high pressure of the blood emerging from the heart. Veins Veins bring back blood from the tissues and organs to the heart. The blood in veins flows under less pressure than that in arteries. Therefore, veins do not have thick walls. But veins can accommodate more blood. Veins have valves that allow blood to flow in one direction only. Capillaries Arteries branch out into smaller and thinner blood vessels called arterioles. These divide into still smaller vessels to provide blood to all the cells. The thinnest blood vessels are called capillaries. Their walls have just one layer of squamous cells. These walls are permeable, so that water and dissolved substances pass in and out, exchanging oxygen, carbon dioxide, dissolved nutrients and waste products with the tissues around the capillaries. The capillaries form a dense network, reaching out to each and every part of the body. The flow of blood is very slow in capillaries. They join to form venules and veins, which return blood from organs and tissues to the heart.

The Human Heart Structure The heart is a muscular, conical and dark red organ that plays the role of a pump in the circulatory system. Its pumping action maintains the circulation of blood. In man, the heart weighs about 0.43 per cent of the body weight. It is located in the middle of the thoracic cavity, but its apex is tilted towards the left side. The heart is enclosed in the pericardium, a tough, inflexible membrane. Between the heart and the pericardium is a fluid which reduces the friction produced during heartbeat. The heart is made up of cardiac muscles. These muscles contract with considerable force, squeezing the blood out into the arteries. The heart beats nonstop throughout one’s life. It is due to the rhythmic contraction and relaxation of the heart muscles. There are four chambers in the heart—two atria, with thin walls, and two ventricles, with thick walls. Working of the heart Blood from different parts of the body comes to the right atrium when it expands. This impure blood is brought from the upper part of the body through the superior vena cava and from the lower part of the body through the inferior vena cava. As the right atrium contracts, the blood goes to the right ventricle, which dilates. The atrioventricular aperture is closed by a valve after the blood transfer. Valves prevent the backflow of blood when the atria or ventricles contract. When the right ventricle contracts, the blood is forced out to the lungs for oxygenation through the pulmonary artery, guarded by another valve. In the lungs, there is an exchange of oxygen and carbon dioxide. After the blood has received oxygen from the lungs and given off carbon dioxide, the oxygenated blood returns to the left atrium. Pulmonary veins bring this oxygenated blood from the lungs to the left atrium, as it relaxes. When the left atrium contracts, blood is transferred to the left ventricle, which expands. The aperture between the left atrium and left ventricle is guarded by a valve. The wall of the left ventricle is three or four times thicker than the wall of the right ventricle, as it pumps blood to the body. When the left ventricle contracts, the oxygen-rich blood is pumped into the aorta for circulation to different parts of the body. The opening of the aorta is also guarded by a valve. Deoxygenated blood is collected from different parts of the body by small veins. These open into larger veins, which bring the blood back to the right atrium.

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Fig. 3.6 Internal structure of the human heart

Cardiac cycle One sequence of the filling of the heart with blood and its pumping is called the cardiac cycle. The phase of contraction of the ventricle is called systole and its relaxation phase is called diastole. Blood pressure As blood flows, it exerts a force on the walls of the blood vessels. This is much greater in the arteries than in the veins. The pressure of flow of blood in the aorta and its main branches is defined as blood pressure. The heart has to develop a high pressure so that blood can be pumped through the arteries, capillaries and veins. During the ventricular contraction, or systolic phase, it is equal to that exerted by a column of 120 mm of mercury. During the ventricular relaxation, or diastolic phase, it is about 80 mmHg. Thus, the normal blood pressure is said to be ‘120/80’. However, the blood pressure varies from person to person and is affected by age, sex, heredity, physical and emotional states, and other factors. An instrument called sphygmomanometer is used to measure blood pressure. Abnormally high blood pressure is called hypertension. It may be associated with a disease or may occur due to anxiety. During hypertension, the arterioles get constricted and increase resistance to blood flow. High blood pressure can cause the rupture of blood vessels, internal bleeding or stroke. If a blood vessel is ruptured in the brain, that part does not get blood, oxygen and nutrients, and loses its function.

Fig. 3.7 Measuring blood pressure (here ‘120/70’) by a sphygmomanometer

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The Lymphatic System Lymph is another type of fluid that takes part in transportation. Blood containing oxygen and food flows under tremendous pressure in the arteries, which divide into arterioles and eventually into capillaries. When the blood from an arteriole enters a capillary, it is under so much pressure and the capillary walls are so thin that a clear liquid is forced out of the capillary walls into the spaces between the surrounding cells. This liquid is called tissue fluid. Tissue fluid carries with it oxygen, food and other useful substances to the cells. It also takes away carbon dioxide and waste products from the cells. If tissue fluid were to accumulate in the tissues and organs, it would cause swelling. So, it is returned to the bloodstream through another system of vessels, called the lymphatic system. The lymphatic system consists of lymph, lymph vessels and lymph nodes. Most of the tissue fluid drains into lymph vessels and flows as lymph. Lymph is similar to blood except that it does not have RBCs and blood platelets, and has a lesser amount of proteins. Therefore, lymph is colourless or slightly yellowish and is similar to blood plasma. The lymphatic system maintains the balance between tissue fluid and blood. Lymph carries digested fat from the intestine and drains excess fluid from the intercellular spaces back into the blood. Before lymph enters the blood, it passes through a number of lymph nodes. These are small globular masses of lymphatic tissue. Lymph nodes produce WBCs that prevent infection.

• POINTS TO REMEMBER • ·

In higher plants, the transport system (vascular system) consists of tubelike structures made up of xylem and phloem tissue. Water and minerals are transported from the roots upwards through xylem tubes. Phloem transports synthesized food from the leaves to the rest of the plant body.

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Water and dissolved minerals are absorbed by the root hairs. Water from the root hairs diffuses through the cortical cells and is pushed into the xylem vessels with the help of root pressure.

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The blood vascular system of higher animals consists of blood, heart and blood vessels.

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Blood consists of liquid plasma and solid corpuscles (RBCs, WBCs and platelets). RBCs carry oxygen. WBCs prevent infection. Platelets help in blood clotting.

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The human heart is a four-chambered pumping organ, consisting of two atria and two ventricles.

The left atrium receives oxygenated blood from the lungs. This blood is sent to the left ventricle, which pumps the blood to different organs. The right atrium receives deoxygenated blood from different parts of the body. It sends this blood to the right ventricle, which pumps it to the lungs for oxygenation. The heart pumps blood through arteries to the different parts of the body. From the different parts of the body, the blood is collected by veins and brought back to the heart. Blood performs several important functions— transport of respiratory gases, nutrients, waste products, etc., regulation of water content, prevention of infection, and so on. The lymphatic system consists of lymph, lymph vessels and lymph nodes. It maintains the balance between tissue fluid and blood by returning tissue fluid to the blood circulation.

• EXERCISES • A. Very-Short-Answer Questions 1. What is translocation? 2. What do you mean by ascent of sap in plants? 3. Which tissue plays the most important role in upward transportation in plants? 4. Name the vascular tissue which transports food from the leaves to different parts of the plant.

5. 6. 7. 8.

Name the three types of blood corpuscles. Why are red blood cells red in colour? What is the main function of white blood cells? Name the two major veins that carry blood from different parts of the body to the right atrium. 9. Which blood vessels bring oxygenated blood from the lungs to the left atrium?

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10. What is the difference between the systolic and diastolic phases of the cardiac cycle? 11. Where is lymph finally drained?

6. Which of the following animals has a single circulation system? (a) Frog (b) Bird (c) Crocodile (d) Fish

B. Short-Answer Questions 1. How is water absorbed by the roots of plants?

II. Fill in the blanks.

2. What are the major differences between arteries and veins?

1. Blood is a liquid _____ tissue.

3. Why is RBC suitable for transport of oxygen in the body? 4. Name the constituents of blood. White blood corpuscles are called the ’soldiers’ of the body. Why? [CBSE] 5. How does blood clot? 6. What is lymph? 7. What is plasma? 8. Write one function each of the following components of the circulatory system in humans. (a) Blood vessels (b) Blood platelets [CBSE] (c) Lymph (d) Heart

C. Long-Answer Questions 1. Briefly describe the structure of the human heart. 2. Mention any five functions of blood.

2. The iron-rich compound in RBCs is _____. 3. Oxygenated blood leaves the heart through the _____, for circulation to different parts of the body. 4. The blood brought into the heart by the pulmonary veins is rich in _____. 5. The capillaries are made up of a single layer of _____ epithelial cells. 6. The normal blood pressure of a young person is _____. 7. Blood pressure is measured by an instrument called _____. E. Diagrammatic Question 1. The diagram below shows the internal structure of the human heart. Label the chambers and the major blood vessels shown.

D. Objective Questions I. Pick the correct option. 1. In plants, the transportation of food materials is carried out by (a) xylem (b) phloem (c) root hair (d) palisade cells 2. In plants, water and minerals are transported by (a) xylem (b) phloem (c) leaves (d) lenticels 3. The capillaries join to form (a) arterioles (b) arteries (c) veins (d) venules 4. What is blood pressure? (a) The pressure of blood on the heart muscles (b) The pressure of flow of blood exerted on the walls of arteries and veins (c) The pressure of blood on the walls of veins only (d) The pressure of blood on the walls of arteries only 5. Which of the following blood vessels have thick, elastic walls? (a) Veins (b) Capillaries (c) Arteries (d) All of these

• ANSWERS • Objective Questions 1. (b) 6. (d)

2. (a)

3. (d)

4. (d)

5. (c)

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• POSTSCRIPT • ·

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The heartbeat is controlled by a pacemaker system. It consists of a sinoatrial (SA) node, atrioventricular (AV) nodes, bundle of His, and Purkinje fibres. The nodes are specialized cardiac muscles that produce electrical impulses (or current). The SA node is buried in the upper wall of the right atrium, close to the opening of the superior vena cava. This node is called the pacemaker, and it produces the mild electric impulse which initiates the contraction of the heart muscles. The instrument used to record the electrical impulse starting from the SA node to the Purkinje fibres is called the electrocardiograph. The graphic

recording done by this instrument is called an electrocardiogram (ECG). The graphic pattern reveals the condition of the heart. The pattern of electrical activity of the heart can also be seen on an oscilloscope screen. R

P

T Q

S

Fig. 3.8 ECG tracing of one cardiac cycle of a normal-

functioning heart. The five waves are customarily named (P, Q, R, S, T).

v

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Excretion

Excretion Chemical reactions occur in the cells of living organisms all the time to carry out the life processes. The sum of these reactions is called metabolism. Metabolism produces useful products as well as toxic (poisonous) by-products. These toxic substances have to be removed as they are harmful if allowed to accumulate. The removal of metabolic waste products from the body of an organism is known as excretion. The major excretory products are carbon dioxide, excess water, and nitrogenous compounds like ammonia, urea, uric acid, etc. Carbon dioxide and water are produced in the process of tissue respiration. Nitrogenous compounds are formed from the breakdown of proteins and amino acids. Water and salts in excess of the body’s needs are also excreted. We acquire most of the water with our food and drink and some by metabolism, e.g., the water produced during cellular respiration. Other excretory products include chemicals from medicines, toxic substances, and circulating hormones that have already served their purpose. We will learn how metabolic wastes get eliminated.

EXCRETION IN ANIMALS Many unicellular organisms like Amoeba throw out their wastes by diffusion from their body surface. Protozoans have no organs for excretion. As they live in an aquatic habitat, their wastes are eliminated by diffusion through the plasma membrane. Simple multicellular organisms like Hydra throw out solid waste matter through their mouth. Higher multicellular organisms have well-defined specialized excretory organs. These organs could be simple tubular structures as in flatworms and leech. The excretory organs of insects (e.g., grasshopper, cockroach and housefly) are also tubular. They remove nitrogenous wastes from the body fluid and help in maintaining the water balance in the body. In vertebrates, the main organs of excretion and maintenance of water balance are the kidneys.

EXCRETION IN HUMAN BEINGS Although the kidneys are the main organs of excretion, the skin, lungs and liver also help in excretion. Skin Our skin has sweat glands, through which we excrete small amounts of water, urea and salts. 30

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Liver The liver excretes bile, which contains bile pigments. These are produced by the breakdown of old RBCs in the liver. As haemoglobin breaks down, its iron is retained, while the pigment (haem) is excreted with the bile. The liver also excretes cholesterol. Lungs The lungs help in getting rid of carbon dioxide, formed as a result of cellular respiration, through exhalation.

Excretory System in Man Our excretory system consists of kidneys, blood vessels that join them, ureters, urinary bladder and urethra. They help produce and excrete urine. There are two bean-shaped kidneys that lie in the abdominal cavity, one on either side of the vertebral column. The kidneys are reddish brown. Each of them is about 10 cm long and weighs about 150 g. Although they weigh less, they receive a lot of blood for filtration. A volume of blood nearly equivalent to that in the whole body passes through the kidneys every four or five minutes. The kidneys produce urine to filter out the waste products, like urea and uric acid, from the blood.

Fig. 4.1 (a) Excretory organs of man (b) Internal structure of a kidney

Urine leaves each kidney through a tube called ureter. The ureters from both the kidneys are connected to the urinary bladder that collects and stores urine. Ureters carry urine from the kidneys into the urinary bladder. The urethra is a canal that carries urine from the bladder and expels it outside the body.

Internal Structure of a Kidney Each kidney is enclosed in a thin, fibrous covering called the capsule. A renal artery brings blood into the kidney, along with nitrogenous waste materials. After filtration in the kidney, the purified blood leaves the kidney through a renal vein. Two distinct regions can be seen in the section of a kidney—(1) an outer, dark, granular cortex and (2) an inner, lighter medulla. The hollow space from where the ureter leaves the kidney is called the pelvis. Each kidney is made up of numerous (about one million) coiled excretory tubules, known as nephrons, and collecting ducts associated with tiny blood vessels. A nephron is the structural and functional unit of a kidney, having three functions— filtration, reabsorption and secretion. A cluster of thin-walled blood capillaries remains associated with the cup-shaped end of each nephron tubule. These capillaries bring blood from the body to the nephron for filtration. The network of capillaries spreads over the nephron tubules also. These capillaries finally carry purified blood to the body.

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Structure and Function of a Nephron A nephron consists of a long coiled tubule and the Malpighian corpuscle. The tubule of the nephron is differentiated into the proximal convoluted tubule, Henle’s loop and the distal convoluted tubule. The distal tubule opens into the collecting duct. At the proximal end of the nephron is the Malpighian corpuscle, which consists of Bowman’s capsule and the glomerulus. Bowman’s capsule is a double-walled cuplike structure which surrounds the dense network of blood capillaries called the glomerulus.

Fig. 4.2 Different parts of a nephron

The process of excretion in nephron The process of excretion may be divided into three stages—filtration, selective reabsorption and tubular secretion. Filtration Filtration of blood occurs under high pressure in the nephrons of the kidney. Blood enters the glomerulus through the afferent arteriole (with a wider lumen) and leaves through the efferent arteriole (with a narrow lumen). Therefore, blood passes through the glomerulus under pressure. This results in filtration of blood. Water and small molecules are forced out of the walls of the capillaries of the glomerulus and Bowman’s capsule and enter the tubule of the nephron. Large molecules remain in the blood of the glomerulus. The filtrate contains water, glucose, salts, urea, vitamins, etc. It is called the glomerular filtrate. Selective reabsorption Some molecules of the glomerular filtrate are selectively reabsorbed into the blood. The glomerular filtrate flows through the proximal convoluted tubule, the U-shaped Henle’s loop and the distal convoluted tubule. It contains many useful substances such as glucose, amino acids and salts. These are reabsorbed by a process, which requires energy. Without reabsorption, these nutrients could have been lost with the urine. The filtrate now contains urea, some salts and water. Reabsorption of solutes into the blood increases the water concentration of the filtrate. Then water is reabsorbed into the blood by the process of osmosis, and the osmotic balance is restored. The amount of water reabsorbed depends on the amount of excess water in the body and that of the dissolved waste to be excreted. This reabsorption of water from the filtrate to maintain the water balance of the body fluid is known as osmoregulation. In this way the kidneys serve as water-conserving organs. After reabsorption from 180 L of filtrate in the kidney, only 1–2 L of urine is produced.

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Tubular secretion Some nitrogenous waste products like creatinin and some other substances like potassium ions are removed from the blood by the distal convoluted tubule, and are then added to the urine. This is called tubular secretion. Control of excretion The urine that is formed continually collects in the urinary bladder. As the bladder expands, its pressure creates an urge to pass urine through the urethra. As the bladder is muscular, the urge to urinate is under voluntary nervous control.

Fig. 4.3 Blood supply to a nephron

Kidney Failure and the Survival Kit—Haemodialysis The kidneys may be damaged due to infection, injury, diabetes, and extremes of blood pressure. A damaged kidney cannot function efficiently to remove urea, ions, water, etc., from the blood. This malfunctioning results in the accumulation of toxic wastes like urea (uraemia), which can lead to death. One of the ways to treat kidney failure is to use a ‘dialysis machine’ that acts as an artificial kidney. It has a long tubelike structure made of Cellophane suspended in a tank (dialyser) of a fresh dialysis fluid (dialysate). The Cellophane tube is partially permeable and therefore allows solutes to diffuse through. The dialysis fluid has the same concentration as normal tissue fluid, but nitrogenous wastes and excess salts are absent. During dialysis, the blood of the patient is withdrawn from an artery and cooled at 0°C. It is maintained in a liquid state by adding an anticoagulant and by other special treatments. It is pumped through the dialysis machine. Here, the nitrogenous waste products from the blood diffuse into the dialysis fluid. The purified blood is then warmed to the body temperature and pumped back into the patient’s body through a vein. The dialyser is specific for each patient to avoid infections. Dialysis through an artificial kidney has to be carried out at frequent intervals. This process of purification of blood is called haemodialysis.

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A dialysis machine works like a kidney except that no selective reabsorption takes place in the former. An artificial kidney (1) helps remove harmful wastes, extra salts and water; (2) controls blood pressure; and (3) maintains the balance of sodium and potassium salts in a patient whose kidneys have failed.

Fig. 4.4 (a) Haemodialysis (b) Dialyser

EXCRETION IN PLANTS Compared to animals, plants do not have a well-developed excretory system to remove nitrogenous waste materials. This is because of the differences in their physiology. Therefore, plants use different strategies for excretion. The gaseous waste materials produced during respiration (carbon dioxide) and photosynthesis (oxygen) diffuse out through stomata in the leaves and through lenticels in other parts of the plant. Excess water evaporates mostly from stomata and also from the outer surface of the stem, fruits, etc., throughout the day. This process of getting rid of excess water is called transpiration. The waste products, like oxygen, carbon dioxide and water, are the raw materials for other cellular reactions. The excess of carbon dioxide and water are used up in this way. The only major gaseous excretory product of plants is oxygen! Many plants store organic waste products in their permanent tissues that have dead cells, e.g., in heartwood. Plants also store waste within their leaves or barks. These wastes are periodically removed as the leaves and barks fall off. Some of the waste products are stored in special cells or cellular vacuoles. Various waste products such as tannins, essential oils, gums, resins, etc., are produced during catabolic processes. Tea leaves, amla and betel nuts (supari) contain tannin. Tannins are found also in the barks of trees. The leaves of many plants, like Eucalyptus, lemon, sacred basil (tulsi), etc., contain essential oils. The rind of oranges and lemons and the petals of flowers like rose and jasmine also contain oils. Some plant wastes are stored as a thick, white fluid. You may have seen a white fluid ooze

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out when you pluck a papaya or a fig or the leaves of yellow oleander (pila kaner). This white fluid is called latex. Gums are a group of sticky, watersoluble wastes found in the common gum tree (babul). Resins are another group of wastes found commonly in the stems of conifers (e.g., pine, fir). Alkaloids are a group of toxic waste products. But some of these are useful to us. Quinine and morphine are medicines derived from alkaloids stored in Cinchona bark and opium poppy flowers respectively. Caffeine found in coffee seeds and nicotine in tobacco leaves are also alkaloids. Organic acids, which might prove Fig. 4.5 Waste products in the leaves of yellow oleander harmful to plants, often combine with excess cations and precipitate out as insoluble crystals that can be safely stored in plant cells. Calcium oxalate crystals accumulate in some tubers like yam (zamikand). Aquatic plants lose most of their metabolic wastes by direct diffusion into the water surrounding them. Terrestrial plants excrete some waste into the soil around them.

• POINTS TO REMEMBER • ·

The removal of metabolic waste products from the body of an organism is known as excretion.

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Vertebrates have kidneys as the main organs of excretion.

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The nephron is the structural and functional unit of a kidney. It consists of the Malpighian corpuscle, the proximal convoluted tubule, Henle’s loop and the distal convoluted tubule.

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Each part of the nephron has a distinct function. The functions include filtration, reabsorption and secretion. Osmoregulation is the process of controlling the water content and the ion concentration in the body of an animal. It helps an organism maintain its osmotic pressure. Plants use different strategies for excretion. They store waste products in cell vacuoles. Waste products like gum, resin, latex, etc., are removed when leaves or barks fall off.

• EXERCISES • A. Very Short-Answer Questions

B. Short-Answer Questions

1. Name three main excretory products of human beings.

1. What is the basic filtration unit in the lungs and in [CBSE] the kidneys?

2. Which part of the body is responsible for excretion in (a) Amoeba and (b) Hydra?

2. What is the fate of the glucose that enters the nephron along with the filtrate?

3. Name the excretory unit of a kidney.

3. How is the amount of urine produced controlled?

4. Mention the three main functions performed by the nephron.

4. Why is the blood in the glomerulus under high pressure?

5. Name the blood vessel which enters the glomerulus and the one that leaves it.

5. Why does selective reabsorption take place as the glomerular filtrate passes through the nephron?

6. What are the excretory products of plants?

6. What do you mean by ‘artificial kidney’?

7. Which procedure is employed in the working of an artificial kidney?

C. Long-Answer Questions 1. What is a nephron? Describe its main parts.

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2. Name the main steps in the process of excretion in the nephron. How does filtration of blood take place in the glomerulus? 3. How do plants get rid of excretory products? 4. Describe the mechanism of urine formation. 5. (a) Draw a diagram of the human excretory system and label the following: (i) Kidney (ii) Ureter (iii) Urinary bladder (iv) Urethra (b) Name the two major components of normal human urine.

II. Fill in the blanks. 1. The cup-shaped called _____.

capsule

in

a

nephron

is

2. The dense network of capillaries in a Malpighian corpuscle is called _____. 3. The bag in which urine is collected is called _____. 4. Each kidney is connected to the urinary bladder by a tube called _____. 5. The kidneys excrete nitrogenous waste in the form of _____ .

E. Diagrammatic Questions 1. Name the blood vessels and the excretory organs shown in the diagram below.

D. Objective Questions I. Pick the correct option. 1. Which of the following is not a part of a nephron? (a) Henle’s loop (b) Proximal convoluted tubule (c) Distal convoluted tubule (d) Cortex 2. Which statement is correct about a human kidney? (a) It is cylindrical. (b) It is bean-shaped. (c) It has 1000 nephrons. (d) It has two ureters. 3. In the glomerulus of a kidney, (a) the afferent glomerular capillaries are wider than the efferent glomerular capillaries (b) the afferent glomerular capillaries are narrower than the efferent glomerular capillaries (c) the afferent glomerular arteriole is narrower than the efferent glomerular arteriole (d) the afferent glomerular arteriole is wider than the efferent glomerular arteriole 4. The network of capillaries in a nephron is (a) the Malpighian corpuscle (b) Bowman’s capsule (c) the glomerulus (d) none of these

2. In the diagram below, label the glomerulus, Bowman’s capsule, the proximal convoluted tubule, the distal convoluted tubule and the collecting duct. Also indicate the afferent and efferent arterioles.

5. Uraemia is a condition developed when (a) a large amount of water is lost in urine (b) there is an increase in urea concentration in blood (c) the urine output is decreased (d) the blood pressure in the afferent arteriole decreases 6. Which of the following substances is/are completely reabsorbed from the filtrate in the renal tubule under normal conditions? (a) Uric acid (b) Glucose (c) Salts and water (d) Urea

• ANSWERS • Objective Questions 1. (d) 6. (b)

2. (b)

3. (d)

4. (c)

5. (b)

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• POSTSCRIPT • An adult skin weighs about 3 kg and has about 8 million sweat glands. During hot weather, we can lose up to 12 L of water and 30 g of salt in a day through sweating.

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One million nephrons are present in each kidney. Each nephron is approximately 5 cm long.

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An adult excretes about 1.6 L of urine every 24 hours.

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About 130 mL of filtrate is formed per minute in the glomeruli of the two kidneys of man. About 99% of the water of the filtrate is reabsorbed as it passes down the nephron. Body salts excreted with human urine may amount to 2.2% and urea 6% of the volume of urine. The yellow colour of urine is due to a pigment called urochrome.

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Control and Coordination

cccccccccccccccccccccccccccccccccccccccccccccccccControl cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc ccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc Coordination OurControl body is and made up of billions of cells that get organizedand intoCoordination different tissues. Different tissues constitute organs, and different organs constitute systems such as the digestive, respiratory and circulatory systems. In order to perform a particular function the component organs of each system depend on each other and work in harmony. In the absence of such working in harmony, an organism cannot do many things that it normally does. For example, when we run, our muscles require greater energy, which can be produced when there is a greater supply of oxygen. To increase the oxygen supply, the rate of breathing increases. When we stop running, our muscles do not need so much energy. Consequently, there is no need for extra oxygen and the rate of breathing comes down to the normal level. All these activities are coordinated and well organized. The working together of various systems in the body is called coordination.

Response and Coordination in Plants and Animals The ability of an organism to detect changes and make appropriate responses is called sensitivity. Anything to which an organism responds and reacts is called a stimulus. In animals the responses are quicker and more obvious. Unicellular animals respond to stimuli either by moving towards them or away from them. In multicellular animals, the process of responding to stimuli is different. The responses occur within seconds, but through a complex network of communication which involves several life processes like movement, locomotion, transport, respiration, etc. For example, when you step out in bright sunlight, you partly close your eyes to keep out the bright light. You may start sweating as the temperature rises. These are coordinated responses to stimuli. Response and coordination in animals involve the sense organs, nervous system and chemical messengers called hormones. Plants also react to specific environmental conditions. However, they have no nervous system and their responses are in the form of slow modified growth or movements called turgor movements, caused due to the distension (swelling) of cells. Let us first examine the phenomena of response and coordination in plants.

RESPONSE AND COORDINATION IN PLANTS Continuous Movements of Plants As a plant grows, the stem tip does not grow upwards in a straight line but follows a curved path. This movement, known as nutation, occurs when at any given time, one part of the apical meristem grows faster than the rest of the stem. The region of more rapid growth moves slowly round the apex. This type of movement is more pronounced in climbing plants such as pea, whose stem tips (or tendrils) twine themselves around a support. The part of the tendril in contact with the support does not grow as rapidly as the part of the tendril away from the object. As a result, the tendril encircles the object and clings to it. 38

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Fig. 5.1 Tendrils in pea

Quick Movements of Plants Rapid movements are uncommon in plants, but some plants do display such movements in response to stimuli. Touch the tip of a sensistive plant (Mimosa pudica) gently. Only a few leaflets close. When you touch it roughly, all the leaflets close.

Fig. 5.2 Response to touch in Mimosa pudica

In Mimosa pudica, the leaflets fold up quickly if any leaflet is touched. How does it happen? It happens because the touch triggers a sudden and rapid loss of water (turgor changes) from cells at the base of the leaflets. These movements of sensitive plants in response to touch are very quick. All quick movements are not so quick. For example, the leaves of many plants, including those of Mimosa pudica, remain open during day. When darkness falls, the leaves fold up. Many flowers open after sunrise and close after sunset. All these movements are directed neither towards nor away from the stimulus. Such movements are called nastic movements.

Stomatal Movements The opening and closing of stomata is controlled by changes in the turgor pressure of guard cells and is coordinated with light and darkness.

Tropic Movements The movement of an organism in the direction of a stimulus or away from it is called tropic movement, or tropism. A tropic movement is said to be positive if it is directed towards the source of stimulus and negative if directed away from the source of stimulus. The plant responds by growth or turgor changes, so that parts of the plant bend towards or away from the direction

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of stimulus. Tropic movements are of different types in response to different stimuli. Growth-related movement of plants is quite slow. Phototropism Phototropism is the tropic response of organisms to light. When a young green plant receives light from one direction only, the stem grows towards the light source. The stem is said to be positively phototropic because the stem tip grows in the direction of light. In order to observe the response of plants to light, you can try the following activity. Take a big cardboard box with a large window cut near its top edge. Keep a small potted plant at the bottom of the box. Take a piece of cardboard with a small window near one edge and fix it in the box as shown in the figure. Cover the box so that light enters only through the window on the top. You will observe that the plant grows towards the light. It will first grow out of the small window in the cardboard. Then it will bend towards the top window and grow out through it.

Fig. 5.3 Phototropism

Sunflower buds exhibit a special type of phototropism in which the buds turn slowly through the day so that they always face the sun. This movement is caused by turgor changes. Geotropism Geotropism is the tropic response of organisms to gravity. When a growing portion of a plant is placed horizontally, the stem tip grows away from the pull of gravity, while the root tip grows towards it. Thus, the stem is said to be negatively geotropic and the root positively geotropic. Place a potted plant horizontally on the ground. After a week, you will see that the stem has bent upwards to grow away from gravity. And if you break the pot and remove some of the soil gently, you will notice that the root has bent downwards to grow in the direction of the pull of gravity.

Fig. 5.4 The stem is negatively geotropic, while the root is positively geotropic.

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Hydrotropism The growth of plant parts towards or away from water is called hydrotropism. Roots are positively hydrotropic, i.e., they grow towards water in the soil. Do you know that the positive hydrotropism of roots is stronger than their positive geotropism? This can be demonstrated by the following activity. Take a sieve or a trough with perforations at the bottom. Put some moist sawdust in it and place germinating seeds on the sawdust. Raise the trough above the surface by keeping a brick under each edge. After a few days you will see that the radicles of the seedlings grow downwards through the pores due to geotropism. These radicles then grow towards the moist sawdust in the trough due to hydrotropism. Perforated trough Moist sawdust Germinating seed

Radicles of seeds Brick

Fig. 5.5 Demonstration of hydrotropism

Due to hydrotropism, the roots of roadside trees often block leaking sewage drains. Chemotropism The tropic response of organisms to chemicals is known as chemotropism. For example, pollen tubes grow towards a chemical produced by the ovule during fertilization. Thigmotropism The tropic response of organisms to touch or contact with a solid surface is called thigmotropism. The climbing parts of a plant that twine around a support are positively thigmotropic. When such a plant part touches a support, the side of its apical meristem in contact with the support grows slower than the other side. This is how tendrils coil around a support.

Plant Hormones Responses and growth in plants are controlled by chemical substances called plant hormones, or phytohormones. These substances are found in very minute quantities in plant tissues. A hormone is produced in specific cells of the plant and is transferred to another part where it influences a specific physiological process. While some plant hormones such as auxins, gibberellins and cytokinins stimulate growth, some others such as abscisic acid retard it. Plant hormones control directional growth in plants and also bring about growth in carefully controlled ways. For example, they help plants to grow leaves only at the nodes and not at other parts of the body. Auxins Auxins are a group of plant hormones synthesized in the apical meristem of the root tips and shoot tips. When a shoot tip receives light, the hormone auxin is synthesized and diffuses towards the shady side of the shoot. This leads to enhanced growth on this side. Thus, the plant bends towards the light. The twining of a tendril around a support is also due to auxins. In many plants, the apical meristem suppresses the growth of lateral, or axillary, buds. The strong influence of the apical bud on the growth of the lateral buds can be seen by removing the apical bud from the plant. Take two potted Coleus plants of almost the same size. Cut off the shoot tip of one plant, but do not disturb the other. Observe and compare the growth of both plants for about ten days. The plant with the nipped-off shoot tip acquires a bushy appearance due to the increased growth of lateral branches. The other plant grows taller with a lesser degree of lateral growth due to the dominance of the apical bud. Regular pruning of the hedges in gardens removes the apical buds and promotes the growth of lateral buds, giving the plants a bushy appearance.

Auxins promote cell elongation, root formation, cell division, respiration and other physiological processes like protein synthesis, water uptake, etc.

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Gibberellins Gibberellins stimulate stem elongation, seed germination and flowering. The maximum concentration of gibberellins is found in fruits and seeds. Gibberellins oppose the effect of abscisic acid, which inhibits growth. Cytokinins Cytokinins are chemicals which promote cytokinesis (cell division). They are produced in dividing cells throughout the plant. In mature plants, cytokinins are produced in the root tips and are transported to the shoots. They also help in breaking dormancy and regulating phloem transport. Abscisic acid Abscisic acid is a growth inhibitor that reverses the growth-promoting effects of auxins and gibberellins. It causes dormancy of seeds, tubers and bulbs. It promotes leaf and fruit fall. It helps in the closure of the stomata to decrease the loss of water.

COORDINATION IN ANIMALS Coordination of the body functions in animals is brought about by the endocrine glands and the nervous system. The substances produced by endocrine glands are called hormones. Some characteristics of animal hormones are as follows: 1. Hormones are different compounds such as proteins, steroids, etc. 2. Hormones are chemical messengers which are discharged in the blood by endocrine glands, from where they reach different parts of the body. 3. A hormone will go to a particular organ and influence its functions. The organ that is influenced by a particular hormone is called the target organ of that hormone. A hormone acts as a trigger or switch. Endocrine glands are directly or indirectly controlled by the nervous system, which receives information about changes in the external environment or internal conditions in the form of stimuli. Control and coordination in animals depend on two things for information transmission— chemical signals of hormones and nerve impulses (electrical impulses). If they depended only on electrical impulses through nerve cells, a limited range of tissues would be stimulated. Since they get chemical signals in addition to the nerve impulses, a large range of tissues are stimulated. As a result, animals can show wide-ranging changes in response to stimuli.

Human Endocrine Glands Hormones are secreted by the endocrine glands, which are ductless glands. We shall now learn about some important endocrine glands in the human body. These are shown in Figure 5.6. Pituitary gland The pituitary is a small gland attached to the ventral side of the brain. The pituitary is the most important endocrine gland, as it secretes a number of hormones that regulate various functions of the body. It also controls the functioning of the other endocrine glands. Therefore, it is called the master gland of the body. The pituitary gland consists of two main parts—the anterior lobe and the posterior lobe. The anterior lobe secretes various hormones. One of these is the growth hormone which regulates growth

Fig. 5.6 Diagram showing the positions of endocrine

glands. In the pancreas, testis and ovary, there are specialized areas for endocrine function. The thymus gland has not been shown because this gland is degenerated or lost in the adult. If present, it is located near the heart.

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and development of the body. It promotes the growth of bones and muscles when the body is growing. An excessive secretion of this hormone leads to gigantism, an abnormal condition of excessive growth. On the other hand, insufficient secretion of the growth hormone in childhood retards growth, leading to dwarfism, an abnormal condition of stunted growth. The anterior lobe of the pituitary gland also secretes hormones that influence the secretion of milk in the mammary glands, the production of sperms in males and the maturing of ova (eggs) in females. Two types of hormones are secreted by the posterior lobe of the pituitary. One of these helps in childbirth and the other influences the reabsorption of water in the kidney. Pineal gland It is a small gland attached to the dorsal side of the brain. It has light-sensitive cells. It controls the biological clock (the timing mechanism by which an organism controls regular activities such as sleeping). Thyroid gland Thyroid is a large gland located behind the larynx (voice box) in the neck. The main hormone secreted by this gland is thyroxine, which contains iodine. Thyroxine controls the metabolism of carbohydrates, fats and proteins, and brings about balanced growth. Excessive secretion of thyroxine is called hyperthyroidism. It increases the general metabolism of the body. As a result, fat stored in the body is depleted and there is a loss of body weight. Insufficient thyroxine secretion is called hypothyroidism. It lowers the general metabolism of the body and increases body weight. By slowing down metabolic activity, hypothyroidism retards body growth and brain development in children. When the thyroid gland becomes overactive and secretes excess thyroxine, it becomes enlarged. As a result, the neck swells up and the eyeballs bulge outward. This is called exophthalmic goitre. Swelling of the thyroid may also be due to the deficiency of iodine in the diet. This is called simple goitre. To prevent this it is important for us to have iodized salt in our diet. Iodine is needed for the synthesis of thyroxine.

Fig. 5.7 An enlarged thyroid gland is

due to goitre.

Parathyroid glands These are two pairs of small glands buried in the thyroid gland. They secrete parathormone, which increases the level of calcium in the blood by taking out calcium from the bones. A certain amount of calcium in the blood is essential for functions such as muscular activity and blood clotting. Thymus gland This gland, located near the heart, is present in newborn babies. It gradually becomes smaller with age and is degenerated or lost in the adult. It produces WBCs which fight infection. Islets of Langerhans The pancreas is a digestive gland located in the C-shaped bend of the duodenum (Figure 5.6). Inside this gland there are groups of hormone-secreting cells. These groups are called the islets of Langerhans. Among the hormones produced by them, insulin is the most important. Insulin controls the rate of oxidation of glucose. It helps the liver and muscle cells to absorb glucose from the blood. It also controls the formation of glycogen from glucose in the liver.

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People who are unable to secrete sufficient insulin suffer from a condition called diabetes mellitus. The level of glucose in their blood keeps on rising, and after a limit the kidney lets the extra glucose be excreted with urine. Doctors advise diabetics to take less sugar in their diet. Some diabetics are advised to take injections of insulin, if they have very high levels of blood sugar. High levels of blood sugar harm the body in many ways. Adrenal glands We have two adrenal glands, one on each kidney. The adrenal glands secrete the hormone called adrenaline or epinephrine. This hormone is secreted when an individual is under great physical or emotional stress or feels threatened by some kind of danger. Excitement generally stimulates adrenaline secretion. Adrenaline increases the heartbeat, rate of respiration and blood pressure. More air is inhaled as the diaphragm and the rib muscles contract, expanding the chest cavity. Adrenaline constricts all the blood vessels except those that supply blood to the heart muscles and skeletal muscles. As the small arteries around the digestive organs constrict, blood is diverted to the skeletal muscles to carry out a response. Adrenaline is called ‘fight and flight’ hormone because there is a surge of adrenaline when a person is fighting or preparing to fight or running away from danger. The changes caused by adrenaline prepare the body to react during an emergency. Hence, adrenaline is also called the ‘emergency hormone’. Testis The main function of the testis is to produce sperms. The testes also synthesize the male sex hormone testosterone. Testosterone secretion begins at the onset of puberty (age of sexual maturity), at 10–12 years of age. It helps in the development of secondary sexual characters in males, e.g., moustache, beard, etc. Ovary At the onset of puberty the ovaries begin to secrete oestrogen, a female sex hormone. Oestrogen produces secondary sexual characters in females and prepares the body for pregnancy. During pregnancy, the ovaries secrete special hormones that help in the development of the baby. Control of Hormone Secretion We have a feedback mechanism for controlling the precise quantity and timing of hormone secretion. For example, when we take a meal, our blood sugar level rises. The response to this stimulus is the secretion of the required amount of insulin. The insulin carries glucose to the tissues. As a result, the blood sugar level falls and insulin secretion is reduced. Such control of hormone secretion helps maintain a state of balance in the body.

THE HUMAN NERVOUS SYSTEM The nervous system performs the following three functions. 1. Sensory input, that is, the detection of stimuli by the receptors, or sense organs (e.g., eyes, ears, skin, nose and tongue) 2. Transmission of this input by nerve impulses to the brain and spinal cord, which generate an appropriate response 3. Motor output, that is, carrying out of the response by muscles or glands, which are called effectors Two types of cells constitute the nervous system— neurons and neuroglia. The neurons conduct impulses and the neuroglia support and protect the neurons. A neuron consists of a cell body called cyton, and two types of processes—dendrite and axon.

Fig. 5.8 A nerve cell (neuron)

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Dendrites or dendrons These are hairlike processes connected to the cyton. They receive stimulus, which may be physical, chemical, mechanical or electrical, and pass it on to the cyton. Cyton It is the cell body, with a central nucleus surrounded by cytoplasm. Axon From one side of the cyton arises a cylindrical process filled with cytoplasm. This process is called axon. It is the longest part of the neuron. It transmits impulse away from the cyton. Its tip has a swelling called axon bulb. Generally, a neuron has one axon. The ending of an axon may be branched. These endings are called synaptic terminals. The gap between a synaptic terminal and the dendrite of another neuron or an effector cell is called a synapse. How do we feel a hot or cold object? How do we feel pain? Why do different things have different smells and tastes? There are thousands of receptor cells in our sense organs. They detect stimuli such as heat, cold, pain, smells and tastes. There are different types of receptors such as algesireceptors (for pain), tangoreceptors (for touch), gustatoreceptors (for taste), olfactoreceptors (for smell), and so on. The stimulus received by a receptor is passed on in the form of electrical signals through the dendrites of a neuron to the cyton of the neuron. The cyton transmits only strong impulses. Weak impulses are not further transmitted. An impulse passed on by the cyton travels along the axon of the neuron. When it reaches the end of the axon, it causes the axon bulb to release a chemical which diffuses across the synapse and stimulates the dendrites of the adjacent neuron. These dendrites in turn send electrical signals to their cell body, to be carried along the axon. In this way, the sensation from the receptor is passed on to the brain or spinal cord. A signal from the brain is similarly passed on to the effector, which carries out the appropriate response. Eat some sugar. You will find it tastes sweet. If you block your nose with your fingers there is no difference in its taste. It still tastes sweet because sugar has no smell that can also contribute to the taste. Block your nose again while eating lunch. You will find that the blocked nose makes a difference in appreciating the taste of various food items. When an item has taste as well as smell, it needs the gustatoreceptors on the tongue as well as the olfactoreceptors in the nose to transmit its stimuli to the brain for the full appreciation of its taste. For example, you may not be able to distinguish between mashed papaya and mashed banana with your nose blocked and eyes closed. The gustatoreceptors and olfactoreceptors together make us appreciate any food better. This is the reason why food seems tasteless when you have a cold and your nose is blocked.

In humans and vertebrates, the nervous system may be divided into the (1) central, (2) peripheral, and (3) autonomic nervous system. Central nervous system The central nervous system consists of the brain and the spinal cord. Brain It is the most important coordinating centre in the body. It is lodged in the brain box, or cranium, which protects it. The brain is covered by membranes called meninges. Between the membranes and the brain and also inside the brain, there is a characteristic fluid, called cerebrospinal fluid. This also protects the brain. The brain may be divided into three parts—forebrain, midbrain and hindbrain. 1. The forebrain (cerebrum) is the anterior part, consisting of two large hemispheres divided by a longitudinal fissure. The surface of the hemispheres has many folds and is called cerebral cortex. The cerebral cortex consists of numerous neurons, and the folds serve to increase the surface area so that the maximum number of neurons can be present. The cerebral hemispheres are seats of intelligence and voluntary action. The forebrain also contains olfactory lobes, which are the centres of smell; and the diencephalon, which has centres of hunger, thirst, etc. To the floor of the diencephalon is attached the pituitary gland. 2. The midbrain includes optic lobes, which are the centres of vision. 3. The hindbrain is the posterior part, located below the forebrain. It consists of the cerebellum, pons and medulla oblongata. The cerebellum is the coordination centre, and maintains the body’s posture and balance. It also controls some precise voluntary actions such as those involved in writing and speech. The medulla oblongata in the brain stem is

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the centre of involuntary actions, like swallowing, coughing, sneezing, salivation, vomiting, heartbeat and breathing. The medulla oblongata is continued into the spinal cord. The pons relays information between the cerebellum and the cerebrum.

Fig. 5.9 Section through the human brain

Spinal cord It is a long cord which arises from the medulla oblongata and runs through the vertebral column (backbone). The vertebral column protects the spinal cord. The spinal cord is also covered by meninges. A cross section of the spinal cord shows the central canal, which is filled with cerebrospinal fluid. Around the canal are clusters of cytons, which form the grey matter. The peripheral part has mainly axons and is called white matter. From each side of the spinal cord two roots, the dorsal and the ventral root, arise. The dorsal root is joined by a nerve called sensory nerve, which picks up sensations from the sense organs (receptors). From the ventral root arises the motor nerve, which takes messages from the spinal cord to the muscles or glands (effectors).

Fig. 5.10 Cross section of the spinal cord, showing how the impact of the hammer was sent to the

dorsal root through the sensory nerve and how the motor nerve brought the message from the ventral root to pull the leg downward. This is an example of reflex action.

Reflex action What happens when you touch something hot or your finger is pricked by a needle? You immediately pull your hand away, without even thinking why you are doing so. Such sudden involuntary responses to stimuli are examples of reflex action. The response may be different when

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your conscious thought process is involved. For example, when a doctor pricks you with an injection needle to inject a medicine into your arm, you do not withdraw your arm immediately. Your conscious thinking tells you that the medicine is being administered to cure your disease. In this case, a message from the spinal cord goes to the cerebrum, the thinking part of your brain, and your thinking brain directs your arm to bear the pain and not pull away. The spinal cord is the centre of reflex action. Reflex actions are produced by reflex arcs, which may be formed anywhere along the spinal cord, nearest to the receptor and effector. A reflex arc is formed by a sensory nerve and a motor nerve joined by a connecting nerve present in the spinal cord. As the impulses do not have to travel all the way to the brain and back, the detection of stimuli and the completion of responses are faster. Reflex action is an extremely quick action, which does not involve any thinking by the brain. If someone hits your leg with a hammer the leg is immediately withdrawn. In this type of reflex action the impact of the hammer (stimulus) received by the receptor is sent to the spinal cord through the sensory nerve. The message is received by the connecting nerve in the spinal cord. The connecting nerve then sends a response through the motor nerve to the muscles (effectors) to pull the leg away (Figure 5.10). Thus, reflex action is a sudden, involuntary motor response to a stimulus. The flow of food in the alimentary canal, blinking in strong light or in response to a sudden movement in front of the eye, sneezing, coughing, yawning, hiccupping, shivering, etc., are also reflex actions. Peripheral nervous system The peripheral nervous system includes 12 pairs of cranial nerves arising from the brain and 31 pairs of spinal nerves arising from the spinal cord. The nerves from the brain and the spinal cord connect the skeletal muscles and control their activity according to the directions and demands of the body. These nerves are, therefore, related to voluntary acts, i.e., they act according to our will. Autonomic nervous system The autonomic nervous system controls and integrates the functions of internal organs like the heart, blood vessels, glands, etc., which are not under the control of our will. The autonomic nervous system has two subdivisions: sympathetic and parasympathetic. The organs receive both sympathetic and parasympathetic nerves. The two types of nerves have opposite effects on the organs, i.e., if one is stimulatory, the other is inhibitory. How does the nervous tissue cause the muscles to act? When an electrical signal from a nerve cell reaches a synapse it causes the axon bulb to release a chemical. This chemical, which is discharged at the junction between the nerve cell and the muscle cell, causes the cell membrane of the muscle cell to move some ions in the muscle cell. This triggers a series of changes, ultimately causing the muscle to contract or relax. • POINTS TO REMEMBER • ·

The working together of the various systems in the body is called coordination.

·

Chemical coordination is seen in plants and animals.

·

·

·

1. Auxins promote cell elongation, cell division, etc. 2. Gibberellins are growth hormones of plants.

Response and coordination in plants are in the form of slow growth and turgor movements. The movement of organisms in the direction of a stimulus or away from it is called tropic movement. Tropic movements are in response to light (phototropism), gravity (geotropism), water (hydrotropism), chemicals (chemotropism) and touch (thigmotropism).

Plant responses and growth are controlled by chemical messengers called hormones. The main plant hormones and their functions are:

3. Cytokinins promote cytokinesis. 4. Abscisic acid inhibits growth. ·

·

Response and coordination in animals involve the sense organs, the nervous system and hormones. A feedback mechanism regulates the action of hormones.

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Gland

Hormone

Effect

Pituitary

Growth hormone

Controls growth

Others

Controls other endocrine glands

Thyroid

Thyroxine

Controls general metabolism

Parathyroid

Parathormone

Controls calcium level in blood

Pancreas (islets of Langerhans)

Insulin

Controls blood glucose level

Adrenal

Adrenaline

Causes excitement, increases blood pressure, heartbeat and respiration rate

Testis

Testosterone

Promotes development of secondary sexual characters in males

Ovary

Oestrogen

Promotes development of secondary sexual characters in females

Animal hormones are produced by ductless glands called endocrine glands, and are discharged in the blood. Some important endocrine glands, their hormones and functions are given in the above table.

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The central nervous system consists of the brain and spinal cord. The brain has three main parts—forebrain, midbrain and hindbrain.

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The spinal cord is the centre of reflex action.

The human nervous system consists of central, peripheral and autonomic parts.

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Reflex actions are quick involuntary responses to stimuli.

• EXERCISES • A. Very-Short-Answer Questions 1. Name any two types of tropism. 2. What happens if a young green plant receives sunlight from one direction only? 3. Mention one important function of gibberellins.

7. Which endocrine gland is called the master gland of the human body? Why? 8. Distinguish between gigantism and dwarfism. 9. Differentiate between the functions of sensory and motor nerves.

4. Name the plant hormone that promotes cell division.

10. Why are diabetes patients treated by insulin injections?

5. What is reflex action?

11. Why is the use of iodised salt advisable?

6. What is synapse?

12. What is a nerve impulse? Which structure in a neuron helps to conduct a nerve impulse (i) towards the cell body and (ii) away from the body? [CBSE]

7. Which part of the brain maintains the posture and balance of the body? 8. Name the two sets of nerves that constitute the peripheral nervous system. 9. Name one hormone which controls growth in animals.

B. Short-Answer Questions 1. What is coordination? Give an example. 2. What are hormones? 3. What are tropic movements? Name the types of tropic movement observed in plants. 4. Differentiate between tropic and nastic movements [CBSE] in plants. Give one example of each. 5. Design an experiment to demonstrate hydrotropism. 6. Where are auxins produced? Mention any two important functions of auxins.

13. Name one hormone secreted by (a) the testis (b) the islets of Langerhans (c) the thyroid gland (d) the ovary C. Long-Answer Questions 1. What is the difference between the movement in a sensitive plant and the movement in our legs? 2. Compare and contrast the systems of nervous and hormonal control in animals. 3. Which gland secretes adrenaline? Why adrenaline called the emergency hormone?

is

4. Briefly describe the structure of the neuron. 5. Explain with an example how a reflex action takes place.

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(a) insulin (c) thyroxine

6. (a) Draw the structure of a neuron and label its nucleus, dendrite, cyton and axon. (b) Name that part of a neuron (i) which receives stimulus (ii) which transmits impulse [CBSE] 7. (a) What is (i) phototropism and (ii) geotropism? Give an activity supported by labelled diagrams to show that light and gravity affect the direction of plant growth. (b) Mention the role of the following plant hormones. (i) Auxin (ii) Abscisic acid [CBSE]

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(b) adrenaline (d) testosterone

7. The seat of intelligence and voluntary action in the brain is the (a) pons (b) cerebellum (c) cerebrum (d) medulla oblongata 8. The activities of the internal organs are controlled by (a) the reflex arc (b) the peripheral nervous system (c) the autonomic nervous system (d) none of these

D. Objective Questions

9. The junction between two neurons is called (a) synapse (b) dendrite (c) joint (d) axon

I. Pick the correct option. 1. The plant hormone essential for cell division is (a) abscisic acid (b) auxin (c) gibberellin (d) cytokinin

10. Reflex action is controlled mainly by the (a) brain (b) autonomous nervous system (c) peripheral nervous system (d) spinal cord

2. The root of a plant is (a) positively geotropic (b) positively phototropic (c) negatively geotropic (d) positively thigmotropic

II. Fill in the blanks. 1. The sensitive plant _____ folds up its leaflets on being touched.

3. Which of these plant hormones is a growth inhibitor? (a) Gibberellin (b) Auxin (c) Abscisic acid (d) Cytokinin

2. In animals, hormones are secreted by _____. 3. Simple goitre is caused by the deficiency of _____ in the diet.

4. The response of plant parts towards light is called (a) geotropism (b) phototropism (c) hydrotropism (d) chemotropism

4. _____ promotes the development of secondary sexual characters in a female.

5. The master gland of the body is the (a) testis (b) pituitary (c) thyroid (d) adrenal

5. The cell body of a neuron is called _____.

6. People suffering from diabetes mellitus are unable to secrete sufficient

8. The _____ gland is located on the kidney.

6. The brain is enclosed in a box called _____. 7. The membranes covering the brain are called _____.

• ANSWERS • Objective Questions 1. (d) 6. (a)

2. (a) 7. (c)

3. (c) 8. (c)

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4. (b) 9. (a)

5. (b) 10. (d)

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Reproduction

Reproduction Reproduction is one of the fundamental attributes of a living organism, through which it is able to produce more of its own kind. Through this process, new individuals are produced, that grow and reproduce again, thus increasing the population of a species. How do we ascertain whether two organisms belong to the same species or not? Consider the example of a common urban crow and a black jungle crow. You may think they belong to the same species because they resemble each other. Actually, however, they belong to two different species because they cannot interbreed. A species is defined as a group of organisms (plants or animals) that can interbreed to produce fertile offspring. Compared to life processes like nutrition, respiration, etc., reproduction may appear to be a waste of energy as it is not essential for the survival of an individual. But it is an important function of a living being as it helps an organism to perpetuate its own kind. Continuity of life, from the time of its origin (millions of years ago) to the present day, has been possible through reproduction.

ORGANISMS PRODUCE SIMILAR OFFSPRING Organisms produce similar offspring, but not exact copies of themselves. The offspring have similar body structures and similar genetic blueprints (DNA) in their cells. At the cellular level, reproduction involves first making a copy of its DNA and creating the cellular apparatus for the new cell. Then the nucleus divides and separates the two copies of DNA. Finally, the cytoplasm divides and separates the cellular apparatus. Thus, a cell divides to produce two new similar cells. DNA carries information for making proteins. Any change, or error, in the copying of the DNA sequence will change the structure of the protein formed. This altered protein may change the basic body design. If this protein happens to be an enzyme then the biochemical reaction it catalyzes will also be affected. Errors in the copying of DNA cause variation (change) in the offspring. Due to this tendency for variation, organisms do not create exact copies during reproduction.

IMPORTANCE OF VARIATION Reproduction involves the replication of DNA. If the replication is exact the body design and features of the organism are maintained across generations. Thus reproduction provides stability to the populations of a species. But reproduction also provides variation. Variation is important for the survival of a species over a period of time, but it may bring advantages and/or disadvantages to the organisms in which it occurs. You will learn more about this in the next chapter. All organisms are exposed to certain environmental conditions. They adapt to cope with even slight changes in the environment. Any drastic change in the environment, like extreme temperature change, varying water level, an earthquake or a meteorite hit, may take a heavy toll 50

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on organisms that are unable to cope with its effects. Variation gives some individuals in a population the ability to cope with changes that others cannot withstand. Suppose, there is a sudden drop in environmental temperature. As a result, some organisms will die due to severe cold. But some of them that have developed the ability to cope with extreme cold will survive and reproduce. This ability comes from variation caused by changes in the DNA. Reproduction in living organisms takes place by two general methods: asexual and sexual.

ASEXUAL REPRODUCTION The type of reproduction that takes place without the process of gamete (sex cell) formation is called asexual reproduction. This type of reproduction takes place commonly in lower plants and animals, where the body is not very complex. There are different forms of asexual reproduction.

Binary Fission Binary fission occurs under favourable environmental conditions. Binary fission is the division of one cell into two similar cells. This is the simplest method of asexual reproduction. It occurs in unicellular organisms like bacteria, yeast, Euglena, Amoeba and Paramoecium. In some organisms (e.g., Leishmania, which causes kala-azar) binary fission takes place in definite orientation due to their specific body structure. Take a permanent slide of Amoeba showing binary fission. Observe it under a microscope. You will see that the nucleus first divides amitotically into two, followed by the division of the cytoplasm. The Amoeba finally splits into two daughter cells.

Fig. 6.1 (a) Binary fission in Amoeba (b) Multiple fission in Chlorella

Multiple Fission Under unfavourable circumstances some unicellular organisms develop a hard protective covering over the cell, called cyst. The nucleus of the cell divides repeatedly, producing many nuclei. Each nucleus is surrounded by a small amount of cytoplasm and many daughter cells are produced within the cyst. When favourable conditions return, the offspring are released. Multiple fission is seen in many algae and the malarial parasite (Plasmodium).

Budding Sometimes new individuals develop from the body wall of the parent as bulblike projections called buds. The buds may be unicellular or multicellular depending upon the type of parent

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organism. The buds finally separate to form new individuals. Budding occurs in yeast, Hydra and sponges. Put some yeast in 10% sugar solution kept in a glass. Cover the glass and keep it in a warm place for a day. The yeast cells grow and reproduce in the sugar solution. These cells are known as a culture of yeast cells. Take a drop of the yeast culture solution on a slide and cover it with a coverslip. Examine it under the microscope. You will see buds on the yeast cells. Fig. 6.2 (a) Hydra and (b) yeast reproduce by budding.

Fragmentation Obtain some pond water. You may see green filamentous structures floating in it. Take some of these structures on a slide. Put a drop of glycerine on them and cover them with a coverslip. Observe under a microscope. The green filamentous structures you see are an alga named Spirogyra, which grows in ponds, ditches and springs. Each filament has a single row of cylindrical cells. Each cell has spiral bands of chloroplasts.

When a Spirogyra filament breaks into pieces, each piece grows into a new filament by cell division. This process is fragmentation. During this process the body of an individual breaks up into two or more parts and each part develops into a complete organism Fig. 6.3 Fragmentation in Spirogyra (Figure 6.3). Some animals like sponges, Hydra and flatworms (Planaria) also reproduce by a similar method known as regeneration. If they are cut into pieces, each piece can regenerate into an entire individual. In complex organisms all cells are not similar. The cells are organized into tissues and tissues into organs. The different organs are placed at definite positions. If such an organism breaks off at any point, the broken part cannot grow into a complete organism with all organs.

Spore Formation Spores are asexual reproductive bodies enclosed in a thick-walled structure called sporangium, which can tide over unfavourable conditions such as extreme heat, dryness, acidity, and so on. Spore formation is a common method of asexual reproduction in many lower forms of life such as algae, bacteria and fungi. Under favourable conditions, the spores are released by the breaking of the thick wall of the sporangium. The spores then germinate into new individuals. In fungi, sporangia burst and release spores (Figure. 6.4). By this method of asexual reproduction, organisms can overcome unfavourable conditions. Some fungi, e.g., Rhizopus and Mucor reproduce by producing spores.

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The fleshy leaves of Bryophyllum bear adventitious buds in the notches along the leaf margin. These buds develop into small plants (plantlets) under favourable conditions. These plantlets can be easily separated to grow as independent plants. Artificial modes of vegetative propagation Farmers, gardeners and horticulturists have developed various artificial methods of vegetative propagation, like grafting, layering, cutting and tissue culture for growing plants in gardens and nurseries. Cutting is a very simple Fig. 6.6 Buds arise from the leaf notches in Bryophyllum method of propagation in which a piece of the parent plant’s stem with nodes and internodes is placed in moist soil. This grows into a new plant. In grafting the cutting of a plant is attached to the stem of a rooted plant. The attached cutting becomes a part of the rooted plant, draws nutrition from it and grows roots at the joint. Now if it is separated, it grows into a new plant. In layering, one or more branches of the parent plant are bent close to the ground and covered with moist soil. The covered portions grow roots and develop into new plants. Cut two pieces from a money plant—one with leaves (i.e., a portion with nodes) and the other without leaves (i.e., a portion of an internode). Place these with one end immersed in water kept in a transparent bottle. Leave them like this for a week. You will see that roots and new leaves grow on the piece with leaves, while the other piece gradually withers. This is because a plant can grow new leaves and branches only if it has nodes. (New leaves and branches arise at the nodes.) The piece of money plant which does not have nodes cannot grow because it cannot produce new leaves.

Tissue culture In this technique some tissue from a desired plant is placed in a suitable nutrient medium under proper conditions. The tissue grows into an unorganized mass, known as callus. A small part of this is put in another medium, which contains growth hormones that induce the formation of plantlets from the callus. When plantlets grow, they can be transplanted in the soil or in pots for developing to maturity. Tissue culture allows us to grow a whole plant from cells taken from any part of the plant body. Many plants can be grown from one parent plant in the laboratory under controlled, disease-free conditions.

SEXUAL REPRODUCTION Sexual reproduction involves the two sexes, namely, male and female. The male sexual unit is known as male gamete, while the female sexual unit is known as female gamete. The formation of gametes and their fusion constitute sexual reproduction. The male gamete is smaller and more active than the female gamete. The female gamete is larger, filled with reserve food and remains passive. The cell formed after the fusion of the male and female gametes is called zygote. The zygote divides repeatedly to form a new individual. Although sexual reproduction also occurs in unicellular organisms like algae and Paramoecium, it is most common in multicellular organisms. Genetic basis and advantage of variations You know that variations help in the survival of a species over time. During asexual reproduction cells divide and DNA replication takes place. At the time of replication, some variation may occur but this variation does not usually cause any drastic change. So, in asexual reproduction offspring are more or less similar to the parent and variation is slow. During sexual reproduction two types of gametes (male and female) are formed. During the fusion of gametes there is recombination of genetic material from two parents. This leads to greater variation in the offspring. As the offspring gets more variations, it is more likely to adjust better to environmental fluctuations.

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Gametes contain half the usual number of chromosomes During sexual reproduction, the combination of DNA from two parents would result in the offspring having twice the amount of DNA. To solve this problem, sexually reproducing individuals have special germ cells (gametes) with only half the normal number of chromosomes and, therefore, half the amount of DNA compared to the other cells of the body. When such germ cells from two individuals unite during sexual reproduction, the normal chromosome number and DNA content are restored. Significance of sexual reproduction Sexual reproduction results in new combinations of genes that are brought together during gamete formation. This reshuffling of genes in the gametes increases the chances of variation in the offspring. Moreover, the combination of two sets of chromosomes, one set from each parent, during zygote formation, leads to variation within a species.

SEXUAL REPRODUCTION IN FLOWERING PLANTS The reproductive part of a flowering plant is the flower. Flowers are considered to be modified shoots.

Parts of a Flower Most flowers have both the male and female reproductive organs, but some bear either the male or the female sex organs. Such flowers are known as unisexual flowers (e.g., watermelon, cucumber, etc.) Those flowers which have both sex organs are known as bisexual flowers (e.g., Hibiscus, pea, etc.) A flower generally bears a long or short axis. This axis has two parts—the stalk of the flower, called pedicel, and its swollen top called thalamus. The parts of a flower are arranged on the thalamus (Figure 6.7).

Fig. 6.7 Diagram of the longitudinal section of a flower

A typical flower consists of four sets of floral parts, or whorls: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels). Calyx and corolla are not directly involved in reproduction. Androecium and gynoecium are directly concerned with sexual reproduction. The androecium is the male part of the flower and consists of stamens. The gynoecium (or pistil) consists of carpels and is the female reproductive part. The whorls are arranged on the thalamus of a flower in a definite sequence.

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Calyx Calyx is the outermost whorl. It consists of sepals. The sepals are usually green, but sometimes they may be coloured. Calyx protects the floral whorls in the bud stage. Corolla Corolla, the next inner whorl, consists of petals. Petals may be white or brightly coloured. They attract insects towards the flower and thus help in pollination. Corolla protects the reproductive whorls in the bud stage. Androecium The stamens are collectively called androecium, which Fig. 6.8 Germination of pollen grains on is the third whorl. Each stamen consists of a filament stigma and fertilization and an anther. Each anther has two chambers called pollen sacs. If you touch the stamens of a flower, a yellowish powder may come off on your hands. Anthers produce these numerous yellowish pollen grains, which contain male gametes. Gynoecium The gynoecium (or pistil) is in the centre of the flower. It is the fourth whorl. It bears the female reproductive organ, called carpel. Each carpel consists of three parts—a basal swollen portion called ovary, a narrow stalklike middle portion called style and a one- to many-lobed flattened disclike sticky structure called stigma at the top of the style. The ovary is surrounded by an outer wall. The ovary may be divided into chambers. The chambers contain ovules. Each ovule has an egg cell (female gamete).

Pollination The transfer of pollen grains from the anthers of a flower to the stigma of the same or another flower is known as pollination. The transfer of pollen to the stigma of the same flower or of flowers borne by the same plant is known as self-pollination (as in pea and Hibiscus). Cross-pollination is the transfer of pollen from the anthers of a flower to the stigma of a flower on another plant of the same species. It is very common in most flowering plants. Pollen can be carried with the help of many agents such as insects, birds, wind and water. Flowers and pollen grains are modified to facilitate the process of cross-pollination. For example, insect-pollinated flowers are colourful so that they attract insects. Wind-pollinated flowers produce light pollen grains which can be carried by the wind.

Fertilization The pollen grains germinate on the stigma after pollination. The inner wall of the pollen grain grows into a pollen tube, which grows down through the style and finally reaches the ovule. Inside the ovule, a male gamete fuses with the female gamete and a zygote is formed. This is known as fertilization. The zygote divides repeatedly to form the embryo (future plant) in the ovule. The embryo possesses a tiny future root (radicle), a tiny future shoot (plumule) and cotyledons to store food. The ovary grows rapidly to form the fruit. The ovary wall ripens and forms the fruit wall. The sepals, petals, stamens, style and stigma of the flower degenerate and usually fall off. Sometimes the sepals may persist in the fruit. The ovule develops into a seed. The wall of the ovule thickens to form the protective seed coat. The seed loses water and becomes hard and dry. Seeds can withstand drought and other adverse conditions in this state. This is an advantage for seed-producing plants. The embryo lies dormant in the seed, but under favourable environmental conditions it becomes active and germinates to form a small seedling. The radicle forms the root while the plumule forms the shoot. The growing root and shoot utilize the food stored in the cotyledons.

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Keep some gram seeds in water for one day. Now take out the soaked seeds from water and keep them at normal room temperature. After 2–3 days remove the seed coat of a healthy seed, separate its cotyledons and place them on a clean glass slide. Observe the parts of the radicle, plumule and cotyledons, with the help of a hand lens.

Fig. 6.9 The embryo has a plumule, a radicle and cotyledons.

HUMAN REPRODUCTIVE SYSTEM Changes in the Human Body When a baby begins to grow, the different parts of its body such as the head, arms, legs and chest grow at different rates. For about the first 12 years of its life it goes through a phase of body enlargement and mental development. During this phase its reproductive organs develop at a slower rate. At about 12 years of age, body enlargement slows down and certain other changes begin to appear. These changes prepare the body for sexual reproduction. This phase is known as adolescence. During this phase, certain parts of the body change in appearance and the person also experiences new sensations such as extreme happiness, sadness, anger, insecurity, and so on. All this is due to the beginning of the secretion of hormones from the ovary and testis. The age when this begins is called the age of sexual maturity (puberty). It varies from person to person. It is marked by the growth of thick hair in the armpits and pubic area. In males, facial hair begins to grow. The vocal cords become wide. Therefore, the voice begins to deepen. The testes become active and begin to produce sperms. The penis and scrotum become larger. In females the menstrual cycle begins and the breasts become enlarged. These changes are slow and take place over six years or so. They serve as signals identifiable by other individuals that sexual maturation is taking place. From this period onwards sexual reproduction becomes a possibility as the body becomes capable of producing the specialized germ cells that are needed for sexual reproduction. But childbearing and lactation (milk secretion) need the female reproductive organs and breasts to be fully developed.

Male Reproductive System The male reproductive organs include the testes, seminal vesicles, penis and some associated glands such as the prostate gland. Testis The most important male reproductive organ is the testis, which produces sperms. There are two oval testes, each contained in a protective bag called scrotum (or scrotal sac), lying outside the abdominal cavity. The scrotal sac can elongate and contract depending upon the body temperature and external temperature. This is necessary because sperm formation occurs at a temperature lower than normal body temperature. The testes produce sperms continuously from the stage of puberty onwards. Sperms from the testis pass through the sperm duct, known as vas deferens. The vas deferens runs anteriorly up to the urinary bladder, from where it leads downward and is joined by a duct from the seminal vesicle.

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Fig. 6.10 Human male sex organs

Seminal vesicle The seminal vesicle is an elongated sac at the base of the urinary bladder. For each testis, there is one vas deferens and one seminal vesicle. The functions of a seminal vesicle are to store the sperms that have come from the testis and to secrete seminal fluid, or semen, in which the sperms float. Prostate gland The sperm ducts from both sides join near the base of the urinary bladder, opening into a single tube called urethra (Figure 6.10). This junction occurs inside the prostate gland. The prostate gland adds its secretion to the seminal fluid. The urethra leads to the outside of the body through an organ called penis. It carries both urine and seminal fluid. Penis The penis is a muscular, tubular organ made up of loose tissue with spaces in between. This is called erectile tissue. On being stimulated, the erectile tissue fills with blood, making the penis erect and firm, so that it may enter the vagina of the female and discharge the sperms. Sperm The sperm is the male gamete. It has a head and a long tail, which helps it swim towards the ovum (egg).

Female Reproductive System The female reproductive organs include the ovaries, Fallopian tubes, uterus and vagina. Ovary The ovaries are a pair of small, oval organs in the lower part of the abdominal cavity. They produce ova. At the time of birth, a female already has thousands of immature ova in her ovaries. Many of these degenerate during childhood. The ova start maturing when the female reaches puberty. Every 28 days, one of the ovaries releases an ovum. When an ovum is released from the ovary, it is taken up by a thin Fallopian tube (also called oviduct) through its funnel-shaped opening. The ovum is passed down the duct and into the uterus, which passes it out of the body through the vagina. The ovum is very small and, therefore, hardly noticeable. Fallopian tube The Fallopian tubes, or oviducts, are a pair of thin tubes that lead from the ovaries to the uterus. Each Fallopian tube has a funnel-shaped opening near the ovary. It is lined by cilia. The movement of the cilia helps conduct the ovum down the Fallopian tube and into the uterus.

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Fig. 6.11 Human female sex organs

Uterus The uterus (womb) is a hollow, pear-shaped, elastic muscular structure. Its upper portion, into which the Fallopian tubes enter, is broader. The narrow lower portion, called cervix, consists of a ring of muscles. The uterus opens into the vagina through the cervix. A fertilized ovum (zygote) develops into a baby inside the uterus. Vagina The vagina is a tube leading to the outside of the body through an opening called vulva. The vagina is the organ where the penis is inserted during intercourse for the discharge of sperms. It is also the passage through which the fully developed baby is born. Fertilization When semen is discharged in the vagina during sexual intercourse, the sperms begin moving up the vagina and uterus, finally reaching the Fallopian tubes. But only one sperm enters the ovum. Most of the sperms die while climbing up the Fallopian tubes. A sperm can remain alive in the Fallopian tube for about 12 hours. In this span of time, if it meets the ovum, it is likely to enter the ovum. This is called fertilization.

Changes after Fertilization Implantation The fertilized egg (zygote) moves down the Fallopian tube and continuously undergoes cell division. Thus it forms a hollow ball of cells, called embryo. The embryo gets embedded in the wall of the uterus, which is thick and has muscles, glands and a large number of blood capillaries. This process is called implantation. Pregnancy The developing embryo at first derives nourishment directly from the mother’s blood flowing in the vessels lining the uterine wall. In about three weeks, it starts absorbing food and oxygen through an organ called placenta. The placenta is a disclike organ in the lining of the uterine wall. It has numerous villi, which are in direct contact with the mother’s blood flowing in the uterine wall. These villi provide a large surface area for glucose and oxygen to pass from the mother to the embryo and for wastes produced by the embryo to be passed into the mother’s blood. The embryo is connected to the placenta by a tube called the umbilical cord. By eight weeks, the embryo starts showing human features and is referred to as foetus. The total period of embryonic development, from the time of fertilization to birth, is called gestation period. It is around 280 days, or 9 months, in humans.

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Birth The wall of the uterus develops a thick layer of muscles during pregnancy. At the time of birth, the uterine muscles contract rhythmically and powerfully, causing labour pains to the mother. Finally, the baby is expelled by the contraction of the uterine muscles. This is called birth or parturition. What happens when the egg is not fertilized If the ovum is not fertilized in the upper part of the oviduct, it keeps on descending and is finally passed out through the vagina. It remains in the body for about 24–72 hours. As an egg is released for fertilization every month, the uterus also prepares itself every month for the implantation of a fertilized egg. The uterus becomes thick-walled and spongy in order to nourish the embryo. If no fertilization takes place, the thick uterine wall is no longer needed. So, it gradually begins to shrink. This shrinkage ruptures its blood vessels. As a result, blood and mucus ooze out of the vagina. This period, which lasts for 3–5 days, is called the menstrual period, and the process is called menstruation. If the ovum is fertilized, it gets implanted in the uterus wall and embryonic development starts. In this case, the uterus continues to develop in order to hold the embryo. And in this case, there is no question of its shrinkage resulting in menstruation.

REPRODUCTIVE HEALTH Reproductive health is concerned with healthy and safe sexual practices. Unhealthy practices can lead to the transmission of diseases from one partner to another and even to the offspring. Reproductive health also depends on healthy behaviour and outlook towards sex life. Sexual maturation and body growth are gradual processes. Even with some degree of sexual maturation, the body and mind are not mature enough for a sexual act, childbearing and bringing up children. Reproduction at an early age, say between 13 and 20 years, is not advisable as the uterus is not completely developed to hold the foetus for the entire gestation period of 9 months. There is a risk that the uterus may rupture or the foetus may be aborted. Also, sexual intercourse involves intimate physical contact between the male and female sex organs. This contact may transmit certain diseases from one partner to another. Such diseases are called sexually transmitted diseases (STDs).

Sexually Transmitted Diseases Sexually transmitted diseases are caused by a variety of microorganisms (such as bacteria and viruses) that live in the warm and moist environments of the vagina, urethra, anus, etc. STDs occur mostly in individuals who are involved in sexual activity with many partners. Bacterial infections Gonorrhoea and syphilis are common sexually transmitted bacterial infections. These are caused by bacteria that infect the ureter in men and the cervix in women. Viral infections Viruses cause STDs such as herpes, genital warts and cervical cancer. AIDS (Acquired Immune Deficiency Syndrome) is caused by the human immunodeficiency virus (HIV), which attacks the immune system and kills people. The primary route of transmission of HIV is sexual, but it is also spread by the use of infected needles among intravenous drug users, by the transfusion of infected blood, and from an infected woman to her foetus during pregnancy. Prevention To prevent sexually transmitted diseases, the following precautions can be taken. 1. Using a protective covering called condom over the penis

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2. Using disposable needles and syringes 3. Not sharing shaving blades or razors 4. Not having multiple sex partners 5. Testing and screening the blood for HIV before transfusing it

FAMILY PLANNING The human population is growing rapidly and this is a major cause for concern. With the increase in population, the resources of the earth will deplete more rapidly. The environment will be adversely affected and it will be difficult to maintain the quality of life of the large population. It is, therefore, extremely important to control population growth. In many countries, as in ours, the population grows rapidly because birth rates are high and death rates are comparatively low. In such countries it is extremely important to have a small family.

Contraception It is possible to limit the size of a family through various means. One is to prevent pregnancy. Fertilization of the ovum and its subsequent implantation is referred to as conception or pregnancy. Prevention of conception is called contraception. Conception can be prevented in the following ways. Mechanical barrier There are a number of methods of contraception that create a mechanical barrier between the sperms and the egg. One method is to use a fine rubber tube called condom. This is worn over the penis during sexual intercourse, so that semen is collected in this tube and not discharged in the vagina. This method also prevents the spread of AIDS and many other sexually transmitted diseases. A diaphragm or cap can be fitted in the cervix of a woman to prevent semen from reaching the Fallopian tube. An intrauterine contraceptive device (IUCD), or loop or copper-T, is another contraceptive device which can be used by a woman to prevent conception. An IUCD is made of plastic or stainless steel. It is inserted in the uterus. Its insertion causes irritation in the uterine lining. As a result, there is a lot of mucus secretion which prevents implantation of the embryo. Chemical methods Oral contraceptives can be taken to change the hormonal balance of the body so that the ovum is not released from the ovary. Since the ovum does not come into the Fallopian tube, it is not fertilized. Oral contraceptives are tablets which a woman has to take every day. These are also called birth control pills. Of all the contraceptive measures, oral contraceptive pills are the most effective. However, the change of hormonal balance caused by the intake of oral contraceptives occasionally has undesirable side effects. Surgical methods If the vas deferens, which carries the sperms to the urethra, is tied by a thread, the sperms cannot go past the tied point. The vas deferens can be exposed by a slight incision at the base of the scrotum. This incision and subsequent ligature (tying by thread) of the vas deferens by a surgeon is called vasectomy. In women, ligature of the Fallopian tube can prevent the passage of ova down the Fallopian tube. This is called tubectomy. Both vasectomy and tubectomy ensure that fertilization will not take place.

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Surgery can also be used for aborting unwanted pregnancies. However, this is often misused for illegally aborting female foetuses. (The killing of a foetus is called foeticide.) To prevent female foeticide, prenatal sex determination has been prohibited by law.

• POINTS TO REMEMBER • ·

Living organisms can reproduce methods: asexual and sexual.

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Asexual reproduction can occur by binary fission, multiple fission, budding, fragmentation, sporulation, and vegetative propagation (in plants).

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Vegetative propagation in plants occurs by means of stems, roots and leaves. It is also done artificially (grafting, cutting, layering, tissue culture) and is applied in horticulture and agriculture.

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Sexual reproduction involves the fusion of male and female gametes.

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Flowers bear the sexual parts of the plant— androecium (male part) and gynoecium (female part). Flowers may be unisexual or bisexual.

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The male gamete of plants is produced in the stamen and the female gamete is produced in the carpel.

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The transfer of pollen grains from the anther of a stamen to the stigma of the pistil is called pollination.

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The fusion of pollen and egg is called fertilization.

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In humans, the male reproductive system consists of the testes, seminal vesicles, penis, and glands such as the prostate gland.

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The testes produce the male gametes (sperms).

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The female reproductive system consists of the ovaries, Fallopian tubes, uterus and vagina.

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The ovaries produce the female gametes (ova). Each month, one ovum (egg) matures and is released from the ovary into the Fallopian tube.

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Semen (containing sperms) is discharged into the vagina during sexual intercourse. If a sperm reaches the Fallopian tube and fuses with an ovum, fertilization occurs and a zygote is formed. Fertilization is followed by the implantation of the embryo in the uterine wall.

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The developing embryo in the uterus obtains oxygen and food from the mother’s blood through the placenta. The umbilical cord links the embryo to the placenta. Childbirth takes place due to the contractions of the uterine walls.

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If no fertilization takes place, the uterine wall disintegrates, resulting in menstruation. Sexually transmitted diseases are contracted when a person engages in sexual acts with an infected person. STDs are caused by microorganisms like bacteria and viruses. HIV infection causes AIDS. Contraception ensures population control.

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• EXERCISES • A. Very-Short-Answer Questions 1. How do the following organisms reproduce? (a) Hydra (b) Yeast (c) Planaria (d) Rhizopus 2. Name the type of fission carried out by Amoeba. [CBSE]

3. Name three methods of asexual reproduction. 4. What is vegetative propagation? 5. Name a plant in which vegetative propagation takes place by means of leaves. 6. Define sexual reproduction. 7. Give one example each of unisexual and bisexual flowers. 8. Why do gametes have half the usual number of chromosomes? 9. Which organ enables the developing foetus to obtain nourishment from the mother’s blood? 10. What is contraception?

11. Name two sexually transmitted diseases caused by bacteria. 12. Write the expanded form of AIDS.

[CBSE]

13. Which virus is responsible for causing AIDS?

[CBSE]

14. Write the full form of IUCD.

[CBSE]

B. Short-Answer Questions 1. Mention two features of asexual reproduction. 2. What are the differences between binary fission and multiple fission? 3. Explain the terms ‘fission’ and ‘regeneration’ as [CBSE] used in relation to reproduction. 4. Mention the various steps of budding in yeast. 5. What is tissue culture? 6. Why is variation beneficial for the species, but not necessarily for the individual?

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5. Which of the following is formed during tissue culture? (a) Embryo (b) Callus (c) Cotyledon (d) Gametes

10. What is meant by implantation of the embryo? 11. What is the vas deferens and what is its function? 12. Differentiate between vasectomy and tubectomy. 13. List any three ways in which AIDS is transmitted. Why is this disease considered so dreadful? [CBSE] 14. Name one sexually transmitted disease caused by a bacterial infection and one by a viral infection. How can these be prevented? [CBSE]

6. The fusion of a male and a female gamete results in the formation of (a) egg (b) sperm (c) spore (d) zygote 7. Which of these secretes seminal fluid? (a) Seminal vesicle (b) Prostate gland (c) Neither of these (d) Both of these

C. Long-Answer Questions 1. Explain vegetative propagation in plants.

8. In which part of the female human reproductive system is the ovum normally fertilized by a sperm? (a) Ovary (b) Oviduct (c) Uterus (d) Vagina

2. Describe the structures and functions of androecium and gynoecium. 3. What is pollination? Differentiate between self-pollination and cross-pollination. Name some agents of pollination.

9. In human females the fertilized egg gets implanted in the (a) uterus (b) vagina (c) ovary (d) ureter

4. What are the changes seen in girls and boys at the time of puberty?

10. The ovary releases an egg approximately every (a) 8 days (b) 14 days (c) 21 days (d) 28 days

5. What happens when the ovum is not fertilized? 6. State the role of (a) placenta and (b) umbilical cord in the development of the foetus.

11. Which of the following is found in men? (a) Vas deferens (b) Fallopian tube (c) Ovum (d) Placenta

7. Give two reasons why a woman should avoid frequent pregnancies. Explain the following methods of contraception giving one example of each. [CBSE] (i) Barrier method (ii) Chemical method (iii) Surgical method

12. Which of these is not a sexually transmitted disease? (a) AIDS (b) Syphilis (c) Typhoid (d) Gonorrhoea

D. Objective Questions I. Pick the correct option.

II. Fill in the blanks. 1. Transfer of pollen from anther to stigma is called _____. 2. Buds are found in the notches of _____ in Bryophyllum. 3. Fruit is formed from _____ .

1. Which of these can undergo fragmentation or regeneration? (a) Sponge (b) Flatworm (c) Spirogyra (d) All of these

4. Ovules develop into _____.

2. Which of the following does not happen in asexual reproduction? (a) Binary fission (b) Multiple fission (c) Fertilization (d) Budding

5. An embryo is formed by the repeated division of _____. 6. The developing foetus obtains nourishment from the mother’s blood through the organ called _____. 7. The gestation period in humans is _____ days.

3. The method commonly used to produce new rose plants is

• ANSWERS • Objective Questions 2. (c) 7. (d) 12. (c)

3. (c) 8. (b)

(b) tissue culture (d) grafting

4. Vegetative propagation can take place by means of (a) roots only (b) stem only (c) roots, stem and leaves (d) none of these

8. What is the effect of inaccurate copying of DNA on reproduction? [CBSE] 9. Mention two functions of seminal vesicles.

1. (d) 6. (d) 11. (a)

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(a) layering (c) cutting

7. What is the importance of DNA copying in reproduction?

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4. (c) 9. (a)

5. (b) 10. (d)

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Heredity and Evolution

Heredity and Evolution

VARIATIONS Any difference between individual organisms or groups of organisms of any species, caused either by genetic differences or by environmental factors, is called variation. Variations can be seen in physical appearance, metabolism, behaviour, learning ability, etc. Variations are due to differences that occasionally appear in genes during their duplication. Duplication of genes is essential for a cell to divide, and this is required for all kinds of reproduction. Hence reproduction is the cause of variations. You will not find much variation among vegetatively propagated potato tubers or Bougainvillea stem cuttings. However, you will find distinct variations among the offspring (progeny) of sexually reproducing animals including humans. Some variations are inherited and are important for evolution. Here we will learn about how variations are created and inherited.

Types of Variations There are two types of variations—germinal and somatic. Germinal, or genetic, variations are caused either by differences in the numbers or structures of chromosomes or by differences in genes (units of heredity). Changes in genes are the primary sources of germinal variations. These variations are heritable. Height and eye colour are examples of germinal variations. Somatic variations may result from several factors such as climate, food supply, environment, and interactions with other organisms. These variations are not due to changes in genes or chromosomes. They are not transmittable to future generations. Hence, they are not significant in the process of evolution.

Heritable Variation Heredity involves the transmission of characteristics from parents to their offspring. Among sexually reproducing organisms, the progeny are not exact duplicates of their parents. They usually vary in many traits. The reason why organisms resemble their parents lies in the precise copying of their genes, which carry hereditary characters from one generation to the next. On the other hand, no two offspring have exactly the same genes. This is because the offspring of sexually reproducing organisms receive varying combinations of genetic material from both parents. Such variations result from mutations (errors in DNA copying). Variations also result from genetic recombination during sexual reproduction. Let us see how heritable variation arises, and how it is passed on to the offspring and accumulated over a period of time to play a role in evolution. 64

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Heritable variation is the result of changes in the arrangement of genes on the chromosomes and changes in the sequence of the bases that constitute DNA. Such changes occur spontaneously and randomly in the DNA, which undergoes duplication just before the cell divides. Duplication is done with great precision, but once in about ten million duplications there is an error as a different base may be put in place of the correct one. This mistake, or mutation, gets copied in subsequent cell divisions. Such spontaneous changes in the DNA are proportional to the number of duplications and cell divisions. With successive generations these variations go on accumulating in the descendants. Hence, those organisms that reproduce at a faster rate accumulate a greater number of variations.

Accumulation of Variations Variations in an individual may be an advantage or a disadvantage for it. It may enable or disable it to cope with changes in the environment. Advantageous variations are selected by environmental factors. For example, bacteria that tolerate low temperatures can survive in a cold wave. Such heritable variations lead to the evolution and formation of new species. An advantage of sexual reproduction is that the variations accumulated in the gametes of each sex are combined when they fuse to form the zygote. Hence an offspring produced from the zygote receives and carries the variations of both the parents. On the other hand, in asexual reproduction, there are minor differences among the offspring. These are due to small errors in DNA copying. As gametes and zygote formation are not involved, the asexually produced offspring are quite similar. They have fewer variations accumulated over generations.

Fig. 7.1 Diversity is created over successive generations. The original organism gives rise to individuals which are similar in body design but have slight variations. Each of them, in turn, gives rise to offspring in the next generation. The offspring too are slightly different from each other. Some differences are unique; others are inherited from their respective parents

HEREDITY One of the most important functions of living organisms is that they breed their own kind. A frog breeds to produce a frog, and a mouse breeds to produce a mouse. Moreover, you must have noticed that children resemble their parents, and brothers and sisters resemble each other more closely than they resemble other people. This means the following: 1. The traits, or characteristics, of a species are passed down from one generation to another. 2. The closer the relationship, the greater is the similarity. This continuity of traits, which is maintained for all species and passed down to succeeding generations, is called heredity. However, along with the similarities between brothers and sisters, there are also some dissimilarities. No two individuals are exactly alike. The dissimilarities are called variations. The study of the pattern of transmission of characters from parents to their offspring is called genetics. What do parents give their children that make them resemble the parents? Both father and mother pass on genes, inherited from their own parents, to their children. Genes are stretches of DNA containing coded information for making proteins. These are found on the chromosomes of cells. Genes are the units of heredity.

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The genetic constitution of an individual organism is called its genotype. The genotype determines the characteristic features of an individual (such as height, complexion, hair colour, etc.), which are slowly expressed during development. These characteristic features of an individual also depend on the environment. The sum of the activities of genes and the impact of the environment on them leads to the formation of visible traits, called phenotype. Observe the following features in your classmates. 1. Note their eye colour and find out how many in your class have black, brown, blue or grey eyes. 2. Also enquire about the eye colour of their parents. Find out if the brown-eyed friend’s parents are also brown-eyed. Record you observations. 3. Similarly, prepare a list of the types of ear lobes your classmates have. Record how many have free ear lobes and how many have attached ear lobes. Find out the types of ear lobes their parents have. 4. These physical features are heritable. Therefore, you will find that one or more of their parents and grandparents too have had these features. The inheritance patterns of eye colour and ear lobe follow certain rules of heredity. They depend on the genetic material contributed by the father and the mother to the child. Thus, the inheritance of each trait depends on paternal and maternal DNA.

Fig. 7.2 The colour of the eye is a heritable variation found in humans.

Mendel’s Laws for the Inheritance of Traits Gregor Johann Mendel (1822–84) was an Austrian monk and botanist. He is regarded as the father of genetics. He applied his knowledge of science and mathematics to his experiments on pea plants and established the principles of genetics. Though the results of his experiments were published in 1866, they remained virtually unknown until 1900. In 1857, Mendel began a series of experiments on the pea plant (Pisum sativum) to study the pattern of inheritance of various characters. He chose pea plants for three reasons. First, pea plants are self-pollinating. Second, they are easy to cultivate. Third, they have sharply defined characters. Mendel chose to study seven different characters in pea plants. Each of these characters such as height, seed shape, seed colour, etc., had two sharply defined and contrasting traits (e.g., tallness and dwarfness, round seed and wrinkled seed, yellow seed and green seed). He crossed a variety of pea plant carrying a particular trait (e.g., tallness) of a character (such as height) with another variety having a contrasting trait (e.g., dwarfness) of the same character. These two plants were considered as the parental generation (P). The generation that was produced by crossing these two was called the first filial generation (F1). When F1 plants were crossed among themselves, the generation that was produced was called the second filial generation (F2). The results of Mendel’s experiments showed the following: 1. Whenever two traits of a character were crossed, the F1 plants showed only one of the traits; the other trait never appeared. It did not matter whether the trait came from the pollen or the egg. 2. The trait that did not appear in F1 reappeared in F2, but in ¼ of the total number of plants. Mendel called the substance responsible for each trait a ‘factor’. He explained that each genetic character was represented or controlled by a pair of unit factors, or elements. (Later on,

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the unit factors became known as alleles or allelomorphs. When the term ‘gene’ was coined and defined, the allele became synonymous with the gene.) One of the alleles came from one parent and the other from the other parent. The first-generation plants of Mendel’s experiment were all tall plants. But the allele representing dwarfness was neither destroyed nor altered. It could not be expressed in the first generation because it was dominated by the allele representing tallness. In other words, the allele for tallness was dominant and the allele for dwarfness was recessive. Notations used in Mendel’s experiments The dominant trait is usually represented by a capital letter. For example, tallness is represented by T and dwarfness is represented by the corresponding small letter t. If tallness is due to a pair of dominant alleles, it is written as TT. If tallness is due to only one dominant allele, it is written as Tt. If both the alleles are recessive, making the organism dwarf, then it is written as tt. A homozygous condition is one in which both the alleles are of the same nature, e.g., TT or tt. A heterozygous condition is one in which the alleles are of different nature, e.g., Tt. When two characters are taken into account, the notation for the homozygous dominant could be AABB, and for the homozygous recessive it could be aabb. Inheritance of one character When the tall plants in F1 were crossed among themselves, the F2 generation had 75% tall plants and 25% dwarf plants. Thus, the phenotype ratio was 3 : 1 (see Figure 7.3). This led Mendel to conclude that the alleles representing dwarfness were intact and were neither lost nor altered. Mendel’s experiment with one character (monohybrid cross) led to the formulation of the law, or principle, of segregation. It states that although the alleles of a character remain together, they are separated in subsequent generations.

Fig. 7.3 Inheritance of traits over two generations

Independent inheritance of two separate characters After studying the inheritance of the contrasting traits of one character, Mendel went on to perform an experiment with two characters (dihybrid cross). He crossed a plant having round and yellow seeds with a plant having wrinkled and green seeds. All the F1 plants had round and yellow seeds. When a certain number of F1 plants were crossed among themselves, they gave rise to four types of seeds. Of these, 315 seeds were round and yellow, 108 were round and green, 101 were wrinkled and yellow, and 32 were wrinkled and green. Hence, their phenotype ratio was about 9 : 3 : 3 : 1 (see Figure 7.4). What does this result indicate? It indicates that the chances for the pea seeds to be round or wrinkled do not depend on their chances to be yellow or green. Each pair of alleles is independent of the other pairs. This is the principle of independent assortment. Mendel’s studies provided a breakthrough in our knowledge of heredity. While formulating the principles of heredity, Mendel stated that the units of heredity (which he called ‘factors’) controlled the inheritance of characters. (This view is radically different from an earlier view held by some scientists. These scientists held that characters mixed like paints of different colours. When brought together in the zygote, they got mixed and could not be separated again. This blending of characters gave rise to intermediate characters.)

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Fig. 7.4 Independent inheritance of two separate characters—seed colour and seed shape

What Mendel could not determine was the nature of the ‘factors’. Now, scientists have not only come to know about the physical location of these hereditary units (genes) but have also discovered their molecular compositions. The unravelling of the physical basis of heredity is regarded as the most fascinating chapter in the history of modern biology. Mechanism of expression of traits A gene contains the information for making proteins in the cell. The proteins synthesized according to this information may be enzymes that catalyse biochemical reactions. Each trait is the outcome of several such biochemical reactions, each of which is controlled by a specific enzyme. If the enzyme is not produced because its gene is absent, that particular reaction will not occur and the trait resulting from its reaction will not appear phenotypically. Thus, each trait is controlled by a gene. Each parent contributes one copy of the gene for a particular character. Thus there are two genes for every character. In the gamete, however, only one copy is present because of reduction division. What Mendel perceived was that each gene (allele) is an independent unit which is neither linked with nor influenced by the other gene. Also, each allele can be separated in gametes.

Determination of Sex Sex determination in humans In human beings, sex is determined by genetic inheritance. Genes inherited from the parents determine whether an offspring will be a boy or a girl. Genes for all the characters are linearly arranged on chromosomes. These include the genes for sexual characters. Generally, characters related to the reproductive system are called sexual characters and those that are not are called vegetative characters. The chromosomes that carry genes for sexual characters are called sex chromosomes, while those that carry genes for the vegetative characters are called autosomes.

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A sex chromosome that carries the genes for male characters is called Y chromosome and one which carries the genes for female characters is called X chromosome. We have a total of 46 chromosomes. Half of them come from the mother and the rest, from the father. Out of these 46 chromosomes, 44 are autosomes and 2 are sex chromosomes. The sex chromosomes are not always a perfect pair. In females there are 44 autosomes and two X chromosomes. In males there are 44 autosomes, one X chromosome and one Y Fig. 7.5 X–Y system of sex determination in man chromosome. So the chromosomes in woman are 44 + XX, while the chromosomes in man are 44 + XY. Let us see the inheritance pattern of X and Y chromosomes. During gamete formation, the normal diploid chromosome number is halved. This is called the haploid condition. All the eggs of a female have 22 + X chromosomes. A male produces two types of sperms—one type bears the 22 + X composition and the other, 22 + Y. Therefore, in every 100 sperms, 50 have Y chromosomes and 50 have X chromosomes. Any one of the two types of sperms can fertilize the egg. If a Y-bearing sperm fertilizes the egg, the zygote has the 44 + XY composition, and the resulting embryo grows to be a boy. When an X-bearing sperm fertilizes the egg, the resulting zygote has the 44 + XX composition. This embryo develops into a girl. All the children inherit one X chromosome from the mother. Therefore, sex is always determined by the other sex chromosome that they inherit from the father. One who inherits the X chromosome of the father is a girl, while one who inherits the Y chromosome of the father is a boy. Role of environment in sex determination Environmental conditions such as temperature around the developing embryo may determine sex in some animals. Such conditions may override the genetic basis. Some animals such as snails can even change their sex, showing that their sex is not genetically determined. Incubation of the eggs of the turtle Chrysema picta at a high temperature produces females. But the incubation of the eggs of the lizard Agama agama at a high temperature produces males.

EVOLUTION Evolution refers to the process by which early organisms of the earth diversified into various new forms through slow but continuous variations. Ever since the appearance of the first living beings on the earth some 3.5 billion years ago, new forms have continuously originated. And, the different forms have undergone modifications and given rise to new forms. The newer forms are sufficiently different to be recognized as new species. They breed amongst their own members and not with the ancestral forms or any other forms. The newly formed species may give rise to still newer species over a period of time . This process is called descent with modification. This is the main theme of evolution. Evolution occurs due to the survival of advantageous variations produced in reproduction.

Sources of Genetic Variation You know that there are two main types of variations—somatic and germinal (genetic). Genetic variation arises due to mutation and it can account for the creation of a new species. Mutation is any change in the structure of a gene. Mutation may lead to a change in the expression of a gene. Such a change may even produce harmful effects in the organism.

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Another source of variation is genetic recombination. It is a natural process due to which the arrangement of genes in the progeny is in a combination that differs from that of the parents. This is because the offspring receive genes from both the parents, and this ensures the transmission of some genetic variability from the parents to the offspring. Mutation and genetic recombination may give rise to new characters due to change in genes. These new characters may help the individuals to adapt to their environment. Sometimes the new characters may not help individuals to adapt. Disease, competition, etc., can eliminate those less well-adapted individuals. The survivors pass on their advantageous characters to their offspring. This enables the offspring to adapt well to their environment. Thus nature selects new characters by favouring some of them and eliminating others. In this way natural selection may lead to the evolution of a new species with new characters. Let us see how variations in a population lead to evolution.

Frequency of Genes in a Population The proportion of a particular allele in a population is called gene frequency. How does gene frequency in a population change? Let us consider the genes of a particular species. All the genes in a population of a species at a given time form its gene pool. The frequency of certain genes in the population of an area can change due to certain environmental factors.

Fig. 7.6 Variations in a population

Let us take an example and observe the results in different situations (see Figure 7.6). Suppose there is a population of red beetles living in some bushes in a particular area of a forest. Let us assume that they can generate heritable variations during their sexual reproduction. In the first situation, a heritable colour variation occurs so that a green offspring is born to its red-coloured parents. The green beetle then passes its green trait on to its offspring. These green beetles living in the green leaves of the bushes escape the notice of crows, while the red beetles, because of their bright colour, are easily spotted and eaten by the crows. As a result, the red beetles are soon eaten up by the crows, while the green beetles survive, reproduce and increase in number. In the second situation, a blue-colour variation arises during the reproduction in red beetles. The blue beetle also gives birth to more and more blue beetles. This change in colour, however, gives no survival advantage over the red variety since the crows easily find and eat both blue and red beetles. Now, suppose a bush fire occurs suddenly and kills a large number of beetles, and all the surviving beetles are, by chance, blue. The progeny of the blue beetles are also blue. The survival of these blue beetles is, however, not a case of natural selection, unlike the survival of the

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green beetles in the first situation. This is a case of genetic drift, that is, a random change in the gene frequency. In the third situation, many of the bushes dry up due to a prolonged dry period. The bushes that survive the drought have smaller leaves. This leads to a food shortage for the red beetles. Incidentally, some beetles in the population are smaller in size on account of a heritable variation. They manage to survive, as they require less food, while most of the large beetles die of starvation. Some young beetles of the large variety Fig. 7.7 A population of beetles survive, but these cannot grow to their full size due to undernourishment. Hence, there are only small beetles. When the drought ends and there is enough food for all the beetles, large beetles reappear, and there are both large and small beetles in the population. The genetically small beetles remain small even when they have more food, but the undernourished beetles, which did not undergo any genetic change, grow to their normal size. In the above situations, we can examine where genetic drift has occurred. In the first situation, natural selection played a part in preserving a certain heritable variation. In the second situation, an accident caused genetic drift. In the third situation, an environmental factor led to the production of smaller beetles although some were also produced due to heritable variation.

Acquired and Inherited Traits From very early times scientists have been trying to explain the origin, evolution and diversity of life forms. In the nineteenth century, however, the idea that complex animals and plants developed by gradual change from simpler forms began to be taken seriously. The mechanism of the origin of new species from the existing species was explained first by Jean Baptiste Pierre Antoine de Monet Lamarck (1744–1829), a French biologist, and then by Charles Robert Darwin (1809–82), a British naturalist. Acquired traits Having accepted the fact that new species have arisen from pre-existing species with modifications, a number of scientists have tried to explain the mechanism by which this might have occurred. The first scientific theory concerning this came from Lamarck. His ideas, written in his book Philosophie Zoologique (meaning ‘philosophical zoology’), published in 1809, are known as Lamarckism. Lamarck observed the changes and adaptations in certain organs in animals. He suggested that favourable changes appear due to the use or disuse of organs over a long period of time. For example, some organs develop in size if they are in continuous use, while their disuse has an opposite effect. He concluded that such characters acquired by an organism during its lifetime are transmitted to the next generation. This inheritance of acquired characters results in the evolution of one or more new species. However, most scientists disagree with this, as it has not been supported by experiments. For example, the offspring of a couple of mice whose tails have been cut off are not born tailless. This was demonstrated by an experiment performed by August Friedrich Leopold Weismann (1834–1914), a German biologist. In sexually reproducing organisms, germ cells are produced in the reproductive organs, while the rest of the body has somatic cells. Changes in somatic cells due to environmental factors are not transmitted to the offspring. This is because a change in a somatic organ caused by a

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physiological response by the body does not bring about a corresponding change in reproductive organs. For example, in the earlier illustration, if beetles starve, their size will get reduced. But if they reproduce, their progeny may not have reduced body size if they get enough food. This means that starvation of the parent beetles does not alter the DNA sequence of their germ cells so as to bring about a variation in the next generation. Even if the reproductive cells suffer from starvation, this does not lead to any change in the DNA. The son of a wrestler is, therefore, not born muscular. Similarly, cutting off the tails of mice do not change the genes of their germ cells. Inherited traits Darwinism is the first modern theory that attempted to explain the origin of new species. Charles Darwin made an extensive study of the flora and fauna of the Galápagos Islands in South America. He came to certain conclusions, which he explained in his book The Origin of Species, published in 1859. Darwin proposed that new species arise by the slow accumulation of advantageous variations over a period of time. Though he did not say how these variations arise, he said that variations are so common in nature that no two individuals are alike.

Fig. 7.8 Charles Robert Darwin

Darwin’s second observation was that although the power of reproduction of organisms is enormous, the population size of any species always remains within a limit. He explained it by saying that overpopulation results in a competition for food and shelter, ultimately leading to a struggle for existence among the members of a species. In such a struggle, those that survive must have some favourable qualities that enable them to overcome the difficult situation. These qualities are advantageous variations. The surviving organisms repeat the process of reproduction. Biologically, a species that can reproduce and leave a large number of offspring is considered successful. When the new generation with advantageous characters begins to reproduce, the situation of overproduction and inevitable struggle is repeated. The survivors will have more advantageous characters that help them to compete and survive. All these new features might make them considerably different from the original forms. These differences, or variations, when accumulated over a long period of time lead to the origin of new species. Thus, selection of advantageous variations by nature leads to the origin of new species Charles Darwin explained the mechanism of origin of new species by natural selection. But his theory fell short of explaining the mechanism or the source of heritable variations. This was explained by Hugo de Vries (1848–1935), a Dutch botanist. According to him, heritable variations arise when there is a change in the genes of the germplasm (protoplasm of a germ cell). He called it mutation. The manner in which heritable variations are passed on to the succeeding generations was explained by Gregor Mendel after he performed his pea-plant experiments. If a particular trait spreads in the population, it means that it is favoured by natural selection. On the other hand, an acquired trait is not transmitted to the offspring. Those animals that do not show enough variations are likely to be wiped out, as they cannot cope with changing circumstances. Genetic variability gives an ability to adapt and adds to the chances of survival of a species. A small population of any species would have fewer mutations, resulting in lesser variability and diminished ability to adapt. For example, the small number of tigers surviving in the world do not have enough variations to adapt well to changes in the environment and hence may become extinct.

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Origin of Life on the Earth Darwin explained the evolution of life from simple to complex forms. Mendel tried to explain the inheritance of traits in living beings. But we are still trying to explain the origin of life on the earth. We can speculate whether life began as a cell or from an inorganic molecule. Probably some of the chemical reactions involved in metabolism began when no form of life existed. Small carbon-containing molecules such as acetic acid and citric acid may have been abundant on the young earth. They took part in chemical reactions that produced larger molecules like amino acids, lipids, sugars and RNA. Gradually, these molecules may have interacted and produced the biomolecules essential for life. The above account of the origin of life is based on the general concepts outlined by Aleksandr Ivanovich Oparin (1924), John Burdon Sanderson Haldane (1928), Stanley Lloyd Miller and Harold Clayton Urey (1953), and Sidney Walter Fox (1965). They believed that life arose on the early earth some 3.5 billion years ago by a series of chemical reactions in the seas. The conditions on the early earth were different from those of the present. Elements such as carbon and nitrogen were not present as their oxides (e.g., CO 2 and NO 2 ), as they are today, but were present as CH 4 (methane) and NH 3 (ammonia). Oxygen was not available as there were no photosynthesizing organisms. Hence the atmosphere was a reducing (electron-adding) one and the synthesis of organic molecules could occur easily. In their experiments, Miller and Urey simulated the prebiotic conditions (that is, when there was no life on the earth) and produced some amino acids (units of proteins) and other organic compounds. Their experiments suggested how these organic molecules were produced on the early earth. In these experiments, a mixture of methane, ammonia, water vapour and hydrogen was circulated through water at a temperature just below 100°C, and sparks were passed through the gaseous mixture to simulate the lightning flashes on the early earth. After several days of experimentation, the colour of the solution changed. The analysis of the liquid showed the presence of simple carbon compounds like several types of amino acids that make up protein molecules essential for life. However, when the experiment was carried out in oxidizing conditions, no amino acids were formed. This suggested that reducing conditions were essential for any prebiotic synthesis of organic molecules. Therefore, we can assume that life cannot arise again on the earth because the reducing atmosphere that was conducive to the formation of biomolecules is no longer present. The life forms present today are diverse. They have been changing and evolving since the time they originated. Let us learn how new species originated from existing ones.

SPECIATION Individuals of a species are similar and they can breed among themselves. At the same time, there are some small, but significant, differences (variations) between the individuals of a species. Heritable variations are transmitted to the offspring. These variations are important as they produce changes in the characters of that particular species. This leads to microevolution, or evolution on a small scale with the emergence of new varieties or new subspecies. To understand how such small variations lead to the formation of a new species, let us take the beetle’s example again. Suppose there are beetles spread over a large area. If the population of beetles gets divided into two subpopulations by a barrier (say, a river or a mountain) then it will be difficult for the members of one subpopulation to go to the other side for mating. Therefore, exchange of genetic material, or gene flow, between them will decrease. They will be restricted to mate within their own subpopulations. In other words, they will be forced to inbreed, or mate with closely related individuals in their own isolated subpopulations. In this process, the recessive mutant genes of each parent have a much greater chance of coming together. The genes will now be expressed giving benefit or harm to the offspring. These new characters, or variations, may be selected by nature and may lead to the formation of a new species. The new generations differ so much from the original population that they can no longer

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interbreed to produce fertile offspring. This leads to speciation, that is, the formation of one or more species from an existing species. After a few years, if a male beetle from one isolated area and a female from another area are brought together, they may or may not mate with each other. If they mate but are unable to reproduce, then they have become two different species. If they are able to reproduce, then they are still the same species. Over many generations, different variations are accumulated in each subpopulation. Suppose, for example, in one area with a beetle subpopulation, crows are scarce due to the presence of eagles. And in another area, crows are present in large numbers. Natural selection will not select the green variety of beetles in the first area as there are no crows to eat the beetles. But the green variety will be selected in the second area as the crows will eat the other beetles there. Thus, natural selection may operate differently on the same variations in subpopulations of different areas. Nature will select those variations that help to adapt better in a particular environment. Over a period of time, the processes of genetic drift and natural selection will cause the two isolated subpopulations to become more and more different from each other. Microevolution is generally a consequence of gene mutation. But larger changes in the genetic make-up, like change in the number of chromosomes, may not allow the germ cells of two subpopulations to fuse together. This prevents interbreeding and causes the emergence of new species. Speciation due to inbreeding, genetic drift and natural selection will be applicable to all sexually reproducing organisms. Geographical isolation does not play any role in the speciation of asexually reproducing organisms. It also does not play any major role in the speciation of self-pollinating plants.

EVOLUTION AND CLASSIFICATION The classification of organisms into a hierarchy of groups, namely, kingdoms, phyla (or divisions), classes, orders, families, genera and species, is based on their similarities and differences. For example, the genus Rana of frogs has several species like clamitans, catesbeiana, tigrina, etc. Although they belong to the same genus, they show subtle variations. Similarities suggest that some similar characters are present in the groups. These characters must have come from common genes, which in turn have come from a common ancestor. To interpret similarities and differences between groups on the basis of their evolution we go down the hierarchy of classification.

Fig. 7.9 The genus Rana of frogs has species like (a) clamitans and (b) catesbeiana.

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Classification shows how closely organisms are related with respect to evolution. It is based on the assumption that each organism has descended from its ancestral type with some modification. There is a hierarchy of characteristics that helped taxonomists to form classification groups. For example, the first level of classification depends on whether the cell has a nucleus or not. Except the members of the kingdom Monera (e.g., bacteria) all other organisms have a true, or well-organized, nucleus. The next level of classification depends on whether the nucleated organisms are unicellular or multicellular. The basis for classifying the multicellular organisms is whether they are capable of photosynthesis or not. The basis for classifying nonphotosynthetic organisms is the presence or absence of the vertebral column in the body. In this way, organisms can be arranged in groups based on their physiological, biochemical, anatomical or evolutionary relationships.

Tracing Evolutionary Relationships In order to find out the evolutionary relationships among organisms, we have to look for their common features. Different organisms would have common features if they are inherited from a common ancestor. Comparative anatomy The study of body parts of animals of a particular group shows how apparently dissimilar animals have quite similar anatomical structures. For example, the forelimbs of man, cat, whale and bat are made up of the same skeletal elements. They have been modified to suit the environmental conditions in which these animals live. These organs are functionally dissimilar but structurally similar. Such organs are called homologous organs. The anatomical similarity points to the existence of a common ancestor from which these organisms have evolved. However, though the wings of a bat and the wings of a bird look similar, they are anatomically dissimilar. Such organs are called analogous organs.

Fig. 7.10 (a) Homologous organs—forelimbs of some mammals (b) Analogous organs—wings

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Comparative embryology A comparative study of the stages of the embryonic development of animals reveals that in their early stages they were very similar. These embryonic stages reflect their ancestry. The embryological stages of an organism give us an idea about the stages of its evolution. For example, when we study the human embryo, we find that at a certain stage it has gills. This suggests that fish is one of the earliest ancestors in the evolution of mammals including human beings.

Fossils Fossils are the remains or traces of organisms that lived in the past. Usually the hard parts of organisms (e.g., bones, shells and teeth) turn to stonelike fossils. Sometimes fossils also include remains like skeletons, the preserved impressions of tracks left by organisms on rocks, and so on. Fossil records are a proof of the changes in and the relationships between various groups of organisms. Palaeontology is the study of fossils. A comparison of fossils and present-day organisms gives the evidence of evolution. It shows how one species gives rise to another species with certain modifications. Palaeontologists have found the fossils of dinosaurs that lived in the Jurassic period (about 200 million years ago). These have some features similar to the reptiles present today. The fossil records of the animal Archaeopteryx that lived about 150 million years ago show that it had some features like birds (e.g., feathers) and some features like reptiles (e.g., claws on wings, and a bony tail). This supports the hypothesis that birds evolved from reptiles.

Fig. 7.11 Fossils of some ancient animals

How are fossils studied? Fossils are found in sedimentary rock. This type of rock is formed by the slow deposition and hardening of sand, stones, clay, etc., over a period of time. The lower layers of the rock are older, while the upper layers are recent. We usually use two ways for dating fossils. One way is to assume that animals that lived and died in recent years would be found buried in the top layers of soil. For example, fossils of horselike animals would be exposed on digging these layers. As we dig deeper, we will find older fossils. We may, for example, find fossils of dinosaurs. Fossils found in the bottom layers are the oldest. These may be fossils of invertebrates that lived in very ancient times. The second way of detecting the age of a fossil is by finding out the age of the

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various layers of rock. This is determined by radiocarbon dating. We can calculate the age of a fossil by finding the ratios of different isotopes of the same element in the fossil material.

Evolution Is a Gradual Process Evolution is a gradual process—no organism evolved suddenly. Complex organs evolved in organisms gradually over generations. But what would have been the advantage of the incipient (primitive) organs evolved in the early stages of evolution? How was each intermediate stage selected during its evolution? For example, how did our eye evolve to its present complex form? And, why were its incipient forms (e.g., eyespots in Planaria) selected by nature? Again, wings in birds are an important adaptation for flight. But the featherlike structures initially formed in primitive birds would have had no advantage in flying. Then why did nature select the early feathers? The answer to these questions is that these features would have had some marginal advantages like providing insulation against cold and hence they were selected by nature. Artificial selection also plays an important role in creating diversity, as the following example shows. Humans have cultivated the wild cabbage plant for thousands of years. By carefully examining variations in these cabbage plants, crossing them and artificially selecting their traits, they got a variety of plants like cauliflower, broccoli, kohlrabi and kale. Thus, through artificial selection, all these different-looking plants were developed from the same ancestor. In nature too, structures that look very dissimilar have evolved from a common ancestral design.

Fig. 7.12 Fossils form layer by layer.

Fig. 7.13 Planaria has simple eyes, or eyespots,

that just detect light.

A study of comparative anatomy and fossils suggests that although the wings of a bat, the flippers of a whale, and the arms of a man look different, they are anatomically quite similar. Comparing the DNA of different species can directly show us how much the DNA has changed during the evolution of these species.

Evolution Is Not Necessarily Progressive We can compare the evolution of different species by studying their evolutionary family tree. In the evolutionary family tree of species, many branches (species) can arise at any stage of evolution. A species may not be eliminated for a new species to emerge from it. Are the new species better than the older ones? Evolution does not always mean that the newly evolved forms are better than those that existed in the past. Evolution simply means the generation of diversity and selection by nature.

Fig. 7.14 Incipient feathers in Archaeopteryx

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Natural selection and genetic drift lead to the formation of a population that cannot breed with the original one any more, as in case of the evolution of humans and chimpanzees from a common ancestor. Scientists have suggested that chimpanzees are our nearest evolutionary cousins. About 99 per cent of our 25,000-odd genes are identical to those of chimpanzees. Scientists have discovered our genetic differences with chimpanzees recently. A gene-by-gene comparison shows that these genetic differences are relatively subtle. But even a difference of one per cent would mean 250 possible mutations. A single change in the DNA bases can produce a dramatic change, so 250 mutations will bring about many variations. Humans are very different from chimpanzees and have not evolved from chimpanzees. Rather, humans and chimpanzees evolved from a common ancestor, and each had a separate course of growth and adaptation. In evolution, the new forms evolved are more complex than their ancestors. It is the adaptability of a species to the environment that supports its survival, not the complexity of the species. Had it not been th e case, simpler forms would not have been living today. For example, bacteria are very simple in form, yet they are surviving today. They are found in hot springs, in deep-sea thermal vents, and in ice sheets. This is because of their adaptability to the changing environment. Each species, whether complex or simple, is subject to natural selection. Each species has to go through the process of natural selection to survive and reproduce. In evolutionary terms, we cannot say that a particular species has a better design than another. Each species is well suited and adapted to its environment and hence is good enough to live and reproduce. Molecular phylogeny The ancestors of different organisms, including humans, can be traced by studying the changes in their DNA. A change in the DNA means a change in its protein sequence. The ancestry, or phylogeny, determined by a comparative study of DNA sequences is called molecular phylogeny. How do we trace a human being’s ancestry by studying DNA sequences? Mutation means any change in the bases of DNA. It occurs when there is any duplication of bases, inversion of bases, deletion of bases, addition of bases, and/or substitution of one base with another. The study of these mutations and the pattern of their inheritance allow us to find out how closely one species is related to another and how and when one form diverged from another. The number of mutations in a particular gene over a period of time enables us to calculate how far back in time one species diverged from another. This is because mutations would accumulate over generations. These mutations can be traced backwards in time to find out at which stage each species diverged from another. The more distantly related the organisms are, the greater is the difference in their DNA. In order to trace the ancestry from the fossil of an organism, its DNA is first obtained. Even one drop of frozen (or preserved) blood is enough to get DNA for the purpose. The sequence of this DNA is determined. A large number of fossils are collected from different geological periods and from different regions. The specific DNA sequence of each is determined and compared with the others. The comparative study enables us to find out what the original sequence was, when it underwent a change, in which form the change was passed down, and so on. In this way we can go back in time and determine the ancestor of an organism. Studies in molecular phylogeny help in the classification of organisms. Human migration A mutation in a person’s DNA is passed down to all the descendants of that person. This means that if the same mutation is present in two individuals, both of them share the same ancestor. These mutations can be hidden when the genes are all mixed up during the formation of gametes and zygote. However, the DNA in mitochondria is passed down intact from mother to child. Moreover, the Y chromosome, which determines maleness, is also passed down intact from father to son. Therefore, by comparing the mutations in mitochondrial DNA and Y chomosomes of individuals all over the world, we can trace when and where those people parted and migrated around the world. A study of the changes in the DNA of human beings from all over the world and a study of human fossils scattered all over the globe have suggested that the first human beings originated

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in Africa. The earliest fossils of modern humans were found in Ethiopia in Africa. These humans were hunters. They lived about 200,000 years ago. Some of them left Africa and migrated to West Asia. From there they migrated to Central Asia, South Asia and East Asia. One group of their descendants migrated down to the islands of Indonesia and to the Philippines and Australia, while another group travelled to Europe. Another group migrated to northern Asia, while yet another group went to North America and onward to South America. These early humans migrated in all directions and mixed with one another. Scientists have come to this conclusion by studying human DNA sequences and Y chromosomes, and by analysing the mutations that occurred in humans over a period of time. Today, you can give your blood to a laboratory and get your ancestry traced. You can also find out in which part of the world your ancestors lived. All this is possible by studying the chromosome and mitochondrial DNA. For example, the earliest known mutation spread outside Africa with the migration of humans some 50,000 years ago. If the Y chromosome of an American contains this particular mutation along with various other mutations, it proves his African ancestry. Thus genetic mutations act as markers, tracing ancestry through time. All human beings of the world, whether they are African or American, share the same gene pool and hence all modern humans belong to the same species—Homo sapiens. There are, however, a large number of genes in the gene pool that serve as the source of individual variations. It is for this reason that no two individuals are identical in looks, abilities, behaviour, etc. Therefore, there is great diversity in human features such as skin colour, height, hair colour, and so on. But there is no biological basis for assuming that humans with different features belong to different races.

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The study of the pattern of inheritance of characters from parents to offspring is called genetics. The hereditary units are called genes. The genetic constitution of an individual organism is called its genotype, while the physical appearance is referred to as the phenotype of the individual. Differences among individual organisms or groups of organisms, caused either by genetic differences or by environmental factors, are called variations. Changes in somatic, or nonreproductive, cells are not heritable. Mendel’s experiments on pea plants established the principles of genetics. He called the substance responsible for each trait a ‘factor’. He postulated the following principles: Life originated about 3.5 billion years ago by a series of chemical reactions in the seas leading to the formatio (a) In a cross between two traits of a character, only the dominant trait appears in the F 1 generation. The recessive trait reappers in the F2 generation.

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Life originated about 3.5 billion years ago by a series of chemical reactions in the seas leading to the information of amino acids and other biomolecules.

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Evolution refers to the process by which early organisms of the earth diversified into various forms through a slow but continuous process.

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Darwin’s theory of natural selection proposed that new species arise by the slow accumulation of advantageous variations over a period of time. Darwin explained that in a struggle for existence, nature selects those organisms that have advantageous variations and eliminates those that do not have these.

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The sources of variations are mutation and genetic recombination.

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Sex is determined by different factors in different species. In humans, sex is determined by the inheritance of the paternal sex chromosome. Inheritance of a paternal X chromosome produces a female, while inheritance of a Y chromosome produces a male.

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Variations may or may not bring survival advantages.

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Each pair of alleles gets separated during gamete formation. This is the law of segregation.

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In a cross involving two or more pairs of contrasting traits each pair of alleles is separated independently of the other pair. This is the law of independent assortment.

Speciation takes place when geographically isolated populations have variations. Natural selection and genetic drift take part in speciation.

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Evolutionary relationships are taken into account in the classification of organisms.

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Evolutionary relationships can be traced by studying homologous and analogous characteristics of different species.

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Fossils help in the study of extinct species.

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Evolution of complex organs like the eyes takes place due to the survival advantages of the intermediate stages of such organs.

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Different organs adapt to new functions in the course of their evolution. Feathers may have evolved for giving warmth and later been adapted for flight. Humans originated in Africa and migrated to different parts of the world. Human ancestry can be traced by tracing the changes in DNA backwards in time.

• EXERCISES • A. Very-Short-Answer Questions 1. Define heredity. 2. What is a gene? 3. Where are genes located? 4. How are germinal variations caused? 5. Who was Gregor Johann Mendel? 6. What is a dominant trait? 7. What is the difference between dominant and recessive traits? 8. Which scientist gave the first modern theory of the origin of new species from existing ones? 9. Mention one similarity between a human embryo and fish.

5. Briefly state Mendel’s findings with respect to (a) dominant and recessive characters, (b) the law of segregation, and (c) the law of independent assortment. 6. Explain the usefulness of comparative anatomy with reference to (a) homologous organs and (b) analogous organs. 7. Who proposed the theory of natural selection? Explain this theory briefly. [CBSE] 8. What is the difference between acquired and inherited traits? 9. Does geographical isolation play a major role in the speciation of a sexually reproducing organism? Explain.

10. Mention two sources of variations.

10. Are acquired traits of an individual inherited? Explain.

11. Define phenotype.

11. Why is the small number of surviving tigers a cause of worry?

12. Who first proposed the theory of inheritance of acquired traits? [CBSE] 13. Is geographical isolation an important factor in the speciation of a self-pollinating plant species?

B. Short-Answer Questions 1. Distinguish between heredity and variations. 2. What is the difference between genotype and phenotype?

12. Describe the different ways in which individuals with a particular trait may increase in a population. 13. How is the equal genetic contribution of father and mother to their offspring ensured? 14. Explain how advantageous variations help an organism survive?

3. What are the similarities between Mendel’s ‘factors’ and the genes as we know today.

15. Explain how sexual reproduction gives rise to more variations than asexual reproduction does. How does it affect the evolution of sexually reproducing organisms?

4. Define homologous organs.

16. Explain whether eye colour is genetically inherited.

5. How do embryological studies provide evidences for evolution? 6. What factors lead to the origin of new species? 7. What are fossils? How do they help us learn about the process of evolution? [CBSE]

C. Long-Answer Questions 1. Explain whether a bacterium or a chimpanzee has a better body design. 2. Trace human migration from the time it began in Africa. 3. Explain the role of fossils in tracing evolutionary relationships. 4. What are variations? Distinguish between germinal and somatic variations.

D. Objective Questions I. Pick the correct option. 1. The genetic constitution of an individual organism is called (a) its genotype (b) its phenotype (c) heredity (d) gene 2. The hereditary units are stretches of DNA called (a) chromosomes (b) traits (c) characters (d) genes 3. Which of the following plants did Mendel choose for his experiments? (a) Pisum sativum (b) Hibiscus rosa-sinensis (c) Mirabilis jalapa (d) None of these

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4. The science dealing with heredity and variations is called (a) palaeontology (b) genetics (c) embryology (d) phylogeny

10. Which of these is not a part of Darwinism? (a) Struggle for existence (b) Overpopulation (c) Natural selection (d) Use and disuse of organs II. Fill in the blanks.

6. Which of the following is not one of Mendel’s laws? (a) Law of dominance (b) Law of segregation (c) Law of independent assortment (d) Law of incomplete dominance

1. The study of the pattern of inheritance of chromosomes from parents to offspring is called _____. 2. The number of X chromosomes in a human ovum is _____.

7. What happened when Mendel crossed two traits of a character (say, tallness and dwarfness) in pea plants?

3. In Mendel’s experiment, the trait which did not appear in the F1 generation was said to be _____.

Both the traits appeared in equal numbers in F1 . The offspring showed a blend of the two traits. Only the dominant trait appeared in F1 . Only the recessive trait appeared in F1 .

4. The number of autosomes in the human zygote is _____. 5. Darwin made an extensive study of the flora and fauna of the _____ Islands in South America.

8. The Japanese are genetically the closest to (a) Indian schoolboys (b) chimpanzees (c) gorillas (d) monkeys

6. The Origin of Species was written by _____ .

• ANSWERS • Objective Questions 1. (a) 6. (d)

2. (d) 7. (c)

3. (a) 8. (a)

4. (b) 9. (b)

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9. The forelimbs of man, cat, bat and whale are (a) analogous organs (b) homologous organs (c) missing links (d) fossils

5. Mendel’s contribution to genetics was the (a) principle of mutation (b) theory of natural selection (c) law of independent assortment of factors (d) principle of genetic recombination

(a) (b) (c) (d)

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5. (c) 10. (d)

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Our Environment

Environment The Our environment of an organism means the physical and biological conditions in which it lives. The physical conditions include soil, light, temperature, etc. And the biological conditions include the other plants, animals and microorganisms around it. A change in any of these conditions can affect the organism. To understand how, we need to look at the different ways in which an organism interacts with others and with its surroundings. In this chapter we will look at the interactions between the organisms of an ecosystem.

ECOSYSTEM An organism cannot live in isolation. It needs other organisms, nutrients from its environment, and so on, to survive. So, nature has provided functional units in which different organisms of a given area can live and interact among themselves and with their surroundings. An ecosystem is a functional unit consisting of all the living beings of an area and the nonliving components of their environment, interacting to form a stable system. There are different kinds of ecosystems. They can be natural ecosystems such as deserts, grasslands, forests and lakes, or man-made ecosystems such as gardens, aquariums and crop fields. An ecosystem may be as small as an aquarium or as big as an ocean. A pond is an example of an aquatic ecosystem. All the algae, plants, insects, microorganisms and fish in the pond, and the water and soil of the pond are part of this ecosystem. The organisms of the pond get everything they need from the pond itself. And they help to keep its water and soil in good condition, replenishing the nutrients they take from them. This makes the ecosystem self-sustaining. Now let us look at the ecosystem of a garden. In a garden you will find different plants and animals such as bees, butterflies, earthworms, frogs and birds. They depend on each other and on the nonliving things like the soil, air and water. For example, the earthworms gets nutrition from the soil. In turn, they keep the soil fertile. So do certain kinds of bacteria living in the soil. Birds, bees and butterflies get food from the plants in the garden. They help to keep the ecosystem working by helping in the pollination of the plants.

Stability in Ecosystems All ecosystems are stable systems. This means that they maintain a natural balance. An ecosystem involves the flows of nutrients and energy (in the form of food). If the organisms living in an ecosystem use up nutrients, like nitrogen, from their environment, without replenishing them, soon the system will collapse. However, a balance is maintained between the availability and use of nutrients by recycling them through natural processes. You already know how things like nitrogen and carbon are recycled in nature. A balance is also required to provide different amounts of energy (from food) needed by different organisms. As we shall see, the numbers of different organisms in an ecosystem are balanced in such a way that each organism gets the required amount of food. For example, in a forest ecosystem, the numbers of the prey (like rabbits) are always more than the numbers of the predator (like foxes), to ensure adequate food for the predator. 82

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Structure of an Ecosystem An ecosystem consists of two components—the abiotic component (nonliving component) and the biotic component (living component).

Fig. 8.1 Components of an ecosystem

Abiotic component The abiotic, or nonliving, component consists of the physical environment, nutrients and climatic factors. The physical environment consists of soil, water and air. Inorganic substances such as carbon dioxide, oxygen, nitrogen, water, phosphorus, sulphur, sodium, potassium and calcium constitute nutrients. Things like sunlight, rainfall, temperature, humidity and atmospheric pressure constitute the climatic factors. Biotic component The biotic, or living, component of an ecosystem can be classified on the basis of how the organisms get their food, i.e., whether they are producers, consumers or decomposers. Producers Organisms which make their own food are called producers. They are also called autotrophs. (In Greek, autos = self, trophe = nutrition.) All green plants and certain blue-green algae act as food producers in ecosystems. Consumers Organisms that depend on other organisms for food are called consumers or heterotrophs. (In Greek, heteros = other.) All animals which eat plants or other animals are consumers. Bacteria and fungi that depend on dead plants and animals for food are also in a way consumers. Consumers can be classified as herbivores, carnivores and omnivores. Herbivores eat only plants and plant products. Cows, deer and rabbits are herbivores. Carnivores eat only the flesh of other animals. Tigers, snakes and hawks are carnivores. Omnivores eat plants as well as the flesh of other animals. Man and crow are examples of omnivores. Sometimes it is useful to classify the consumers in an ecosystem on the basis of ‘who eats whom’. Primary consumers are those who feed directly on the producers (plants). In other words, herbivores are primary consumers. Carnivores who feed on plant-eating animals (herbivores) are secondary consumers. For example, a grasshopper that feeds on plants is a primary consumer, and the frog that eats the grasshopper is a secondary consumer. The frog could be eaten by a larger carnivore like a snake. A carnivore that feeds on smaller carnivores is called a tertiary consumer. This consumer may be eaten by the largest carnivore, or the top carnivore, of the ecosystem. The top carnivore is not killed and eaten by other animals of the ecosystem. The top carnivore belongs to a higher order of consumers. For example, a hawk could be the top carnivore of an ecosystem. Other examples of top carnivores are tigers and lions. (Primary, secondary and tertiary consumers are also called consumers of the first, second and third order respectively.) Decomposers Organisms which feed on dead plants and animals are called decomposers. Decomposers are also called saprotrophs or saprophytes (in Greek, sapros = rotten). They include bacteria, fungi and worms. Decomposers break down (decompose) the compounds present in dead plants and animals into simpler substances and obtain nutrition from them. The substances formed in decomposition are released into the soil and the atmosphere. Thus, decomposers play

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an important role in the recycling of materials, replenishment of the soil’s nutrients, etc. They also clean up our surroundings by decomposing dead organisms and wastes from animals and plants. Take a large glass bowl or jar and put some soil and aquatic plants in it. Fill three-fourths of the bowl with water and place it near a window through which sunlight comes in. Put some fish in the bowl. You will need to put some fish food in the bowl from time to time. The oxygen needed by the fish will be liberated by the aquatic plants through photosynthesis. After a few days the water in your aquarium will become dirty. This is because of the waste generated by the fish and the plants. We do not need to clean natural aquatic ecosystems like ponds and lakes. In these, wastes are consumed by decomposers.

Food Chain For an ecosystem to work, there has to be a flow of energy within it. The organisms of the ecosystem need energy in the form of food. The ultimate source of this energy is the sun. Producers like green plants trap solar energy and convert it into the chemical energy of food. When a primary consumer eats the producer, a part of this energy is passed on to it. The primary consumer is then eaten by a secondary consumer. And the secondary consumer may be eaten by a tertiary consumer, and so on. In this way energy gets transferred from one consumer to the next higher level of consumer. A series of organisms through which food energy flows in an ecosystem is called a food chain. It may also be defined as follows. A food chain in an ecosystem is a series of organisms in which each organism feeds on the one below it in the series. In a forest ecosystem, grass is eaten by a deer, which in turn is eaten by a tiger. The grass, deer and tiger form a food chain (Figure 8.2). In this food chain, energy flows from the grass (producer) to the deer (primary consumer) to the tiger (secondary consumer).

Fig. 8.2 A food chain in a forest ecosystem

A food chain in a grassland ecosystem may consist of grasses and other plants, grasshoppers, frogs, snakes and hawks (Figure 8.3).

Fig. 8.3 A food chain in a grassland ecosystem

In a freshwater aquatic ecosystem like a pond, the organisms in the food chain include algae, small animals, insects and their larvae, small fish, big fish and a fish-eating bird or animal (Figure 8.4).

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Fig. 8.4 A food chain in a freshwater pond

A food chain always begins with producers. Herbivores (plant-eaters) come next in the chain. They are consumed by carnivores (flesh-eaters). A few food chains can be long and may extend to the fourth, fifth or even sixth order of consumers. Some common food chains are mentioned below. Plants ® Deer ® Lion Plants ® Worm ® Bird ® Cat Plants ® Grasshopper ® Frog ® Snake ® Hawk Algae ® Small animal ® Small fish ® Big fish ® Bird

Food Web A food chain is a linear arrangement of animals. It does not give a complete picture of the feeding relationships among the different organisms of an ecosystem because many of them eat more than one kind of food. For example, a snake does not eat only mice. It may eat insects, frogs, small birds, etc. Snakes, in turn may be eaten by hawks, eagles, peacocks, owls, etc. Thus, an organism can be a part of many food chains. Different kinds of linked food chains exist in an ecosystem. These food chains form a network of interconnected food chains, called a food web.

Fig. 8.5 A simple food web of a grassland ecosystem

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A food web is a series of interconnected food chains representing the feeding relationships of the organisms within an ecosystem. A food web of a grassland ecosystem is shown in Figure 8.5. Unlike a food chain, a food web has several alternative pathways for the flow of energy. In the food web of a grassland ecosystem shown in Figure 8.5, there are five food chains. 1. 2. 3. 4. 5.

Plants Plants Plants Plants Plants

® ® ® ® ®

Grasshopper ® Hawk Grasshopper ® Lizard ® Hawk Rabbit ® Hawk Mouse ® Snake ® Hawk Mouse ® Hawk

Trophic Levels Sometimes it is useful to study an ecosystem by grouping its organisms by their positions or levels in food chains. A level or position in a food chain is called a trophic level. A particular trophic level consists of the organisms that occupy the same position (say, of primary consumers) in food chains. Energy and materials are transferred from one trophic level to another. The producers in a food chain are at the first trophic level. The herbivores, which feed upon plants, are at the second trophic level. The carnivores, which feed upon herbivores, are at the third trophic level, and so on. So, each trophic level supports the one above it in terms of food.

Fig. 8.6 Trophic levels

In a simple food chain of a grassland ecosystem, there are three trophic levels. Grass (producer) is at the first trophic level. Deer (herbivore) is at the second trophic level and lion (carnivore) is at the third trophic level. What would happen if all the organisms of a trophic level are removed? The natural balance would be disturbed and the results would be disastrous. For example, in a grassland ecosystem, if all the carnivores (like lions) at the third trophic level are removed, the numbers of herbivores (like deer) in the trophic level below would go on increasing. Their numbers would soon be more than that can be supported by the plants of the region. They would eat up all the plants and turn the area into a desert.

Flow of Energy You know that there is a flow of energy in the form of food within an ecosystem. The flow of this energy is unidirectional, i.e., it flows in one direction—from the producers to the consumers at successively higher trophic levels. This energy cannot flow back because a higher-level consumer such as a snake cannot be food for a lower-level consumer such as a rabbit. Let us now look at the flow of energy a bit more closely.

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Fig. 8.7 Flow of energy in an ecosystem

Green plants absorb a very small fraction (about 1%) of the solar energy reaching the outer part of the atmosphere. Through photosynthesis they convert this energy into chemical energy, which is stored as food (carbohydrates). A part of the trapped energy is used by plants in metabolic activities like the growth of new tissues, and a part of it is lost into the surroundings as heat. The remaining energy is available as food to primary consumers. Thus we see that only a fraction of the energy absorbed by plants is finally available to the next trophic level. When primary consumers like deer eat plants, they get the available energy in plants. Some of this energy is used for activities like moving, digesting, etc., and some of it is lost as heat. Only about 10% of the available energy in the food gets transformed into new tissues (flesh) of the deer. This is available to the carnivores (secondary consumers) at the next trophic level. At this level too, the usage, loss and storage of energy follow the same pattern. And this continues at every trophic level. Apart from this, energy from dead plants and animals is transferred to the decomposers. We find that when energy flows from the producers to the consumers at different levels, there is a loss of energy at each trophic level. It has been found that only about 10% of the energy available to a trophic level is transferred to the next higher level. This is called the ten per cent law. Let us look at an example. If 10,000 kilocalories of energy are available to grass (producers), 1,000 kilocalories of energy would be available to grasshoppers (primary consumers), 100 kilocalories would be available to frogs (secondary consumers) and only 10 kilocalories would be available to snakes (consumers of the third order). After this, very little energy would be left for the next level. So, food chains generally have up to three or four trophic levels.

Fig. 8.8 Ten per cent law of transfer of energy

Now, the organisms at a trophic level are food for the organisms at the next higher trophic level. But there is a loss of energy as one goes from a lower to a higher trophic level. Therefore, the organisms at the higher level need to eat a large amount of food to fulfil their requirement of energy. So, the number of organisms at a lower trophic level is usually more than that at the next higher trophic level. If the numbers of organisms at different trophic levels are represented graphically, a pyramid is formed, which is called the pyramid of numbers.

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Fig. 8.9 Pyramid of numbers

Biological Magnification Producers like plants and algae take in nutrients from their surroundings. Sometimes they also take in harmful chemicals along with the other nutrients. These harmful chemicals include compounds of mercury, and chemicals like DDT, which is widely used to kill mosquitoes. These chemicals cannot be broken down by plants and other organisms. So, they accumulate in their bodies. Since organisms at a higher trophic level eat many lower-level organisms, the amount of chemicals entering their bodies increases. Thus, as the chemicals pass on from one level to the next in the food chain, the amount of chemicals accumulated in organisms at each level increases. The progressive increase in the accumulation of a harmful substance in organisms at successively higher trophic levels is called biological magnification or biomagnification. How does biological magnification harm different animals? It has been observed that birds in which DDT has accumulated lay eggs with very thin shells that break easily, even before chicks are born. This affects the growth of their population. In Japan, a mercury compound from a factory was dumped in the waters of Minamata Bay. The mercury found its way to humans who ate fish in which mercury had accumulated. More than a thousand people died as a result. Many countries have banned the use of DDT and the use of mercury in things like batteries.

HOW WE AFFECT THE ENVIRONMENT Human activities can have a harmful effect on the environment. A large number of environmental problems arise due to the wastes we generate and the substances, like CFCs (chlorofluorocarbons), that we release into the environment.

Human-generated Waste A thing which is of no use to us or which we throw away is called waste. Waste includes sewage and garbage. Used water and the waste materials produced by human bodies are carried away through underground pipes as sewage. Garbage refers to the solid household waste that we throw away regularly.

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Garbage may have food scraps, paper, plastic materials, polythene, packing materials, wood, glass, and a host of other items. As our economic and social conditions are improving, we are generating more waste. For example, we are using more paper for newspapers, coupons, posters, and so on. This results in more waste paper. We are also buying more appliances, clothes, etc. Each of these comes with packing materials, which we are throwing out as waste. Biodegradable and nonbiodegradable materials Waste materials can be classified on the basis of whether they can be degraded, or broken down, by biological processes. Materials that get broken down by living organisms are called biodegradable materials. These are substances of plant or animal origin such as paper, wood, cotton, food materials and sewage. So, biodegradable wastes can be broken down into simpler, natural substances by decomposers (saprophytes) such as bacteria and fungi. These substances are harmless and nontoxic. Materials that cannot be broken down by living organisms are called nonbiodegradable materials. Metals, plastics, DDT, detergents, certain dyes, etc., are some examples of nonbiodegradable substances. Nonbiodegradable materials are major pollutants. They may be chemically less active. So they remain unchanged in the environment for a long time. You have already seen how harmful materials like DDT and mercury can be. Plastic bags, bottles, etc., often find their way to drains, etc. Since they do not decompose, they keep on adding up and finally, they choke the drains. Nonbiodegradable detergents, dyes, etc., get into the soil and water bodies and harm the organisms living there.

Fig. 8.10 Nonbiodegradable wastes

Dig a pit in your garden. Put in alternate layers of waste and soil in the pit. The layers of waste can consist of shredded vegetable peels, used tea leaves, stale food, etc. Also add layers of waste paper, torn clothes, leaves, polythene bags, broken glass, plastic bottles, broken wooden articles, and so on. Spray this layered pit with water and cover it with at least 15 cm of soil. Dig up the pit after 15 days. You will find that decomposition has started in the kitchen wastes, waste paper, cotton clothes and wooden articles, as they are biodegradable. Polythene bags, broken glass, plastic bottles, etc., remain unchanged since they are nonbiodegradable.

In general, we should try to use biodegradable materials wherever possible to reduce the harmful effects of nonbiodegradable materials. For certain things, we have a choice between biodegradable and nonbiodegradable materials. For example, disposable cups can be made from nonbiodegradable plastics or from paper (biodegradable) or clay. We should weigh the environmental impact of using a certain material. Although paper is biodegradable, using more paper means cutting more trees. Some may say that good quality clay can be put to better uses like agriculture. But since nonbiodegradable plastic is not a good choice, we have to choose

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between clay and paper. In future we can perhaps use biodegradable plastics. Such plastics are already being used to make disposable cutlery, capsule covers, etc. Remember that some nonbiodegradable materials like glass, metals and certain plastics can be recycled or reused. This lessens their harmful effect on the environment. Management of garbage and sewage Management of garbage and sewage involves collecting, transporting and disposing waste. Garbage is collected by municipal bodies or private agencies. In many cities, garbage-disposal bins are provided in each neighbourhood. There may be separate bins for biodegradable kitchen wastes and for recyclable materials like paper, glass, metals and plastics. When separate bins are not provided, ragpickers pick out plastics, paper, etc., from the garbage and sell them to people who recycle the material.

Fig. 8.11 Garbage bins for different types of waste

Collected garbage is transported to disposal sites by special trucks or tractors. Recyclable solid waste is sent for recycling. The rest is used to fill up land at landfill sites. Sometimes, the solid waste is burnt. This is especially so for hospital wastes and wastes that can pollute the soil. Sewage is carried by pipes to sewage-treatment plants. Here the sewage is filtered and the organic material in the sewage is allowed to settle down and decompose in large tanks. The water coming out of these tanks is clean and is released into water bodies. In some places, sewage is used to produce biogas used for cooking and electricity generation.

Fig. 8.12 Sewage carried by pipes entering treatment tanks, at left

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CFCs and the Ozone Hole High above the surface of the earth, there is a layer in the atmosphere that is rich in ozone (O3). Ozone, which is made up of three atoms of oxygen, affects our respiratory system. However, the layer of ozone in the atmosphere protects us by absorbing the ultraviolet (UV) radiation from the sun. This prevents the harmful UV radiation from reaching the surface of the earth. Ultraviolet radiation can cause skin cancer and cataract. It also affects plants. Ozone is formed at the higher levels of the atmosphere. When UV radiation falls on oxygen molecules, the high energy of UV radiation splits molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine with molecular oxygen to form ozone. UV

¾¾¾¾® O +

O2

radiation

O +

O

O 2 ¾® O 3 (ozone)

Unfortunately, the amount of ozone in the ozone layer is being depleted due to the release of certain chemicals into the atmosphere. Among these chemicals are chlorofluorocarbons (CFCs), which are made of carbon, fluorine and chlorine. CFCs are used in air-conditioners, refrigerators, aerosol sprays, shaving foam, fire extinguishers, etc. These compounds rise up high in the atmosphere and break down to form chlorine atoms. These chlorine atoms react with the ozone to form oxygen. Cl

+

chlorine atom

O3

ozone

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ClO chlorine monoxide

Fig. 8.13 Formation of the ozone hole

+

O2 oxygen

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As ozone gets converted to oxygen, the amount of ozone in the ozone layer decreases. Over time this has created an ozone-deficient area in the atmosphere. This area is called the ozone hole. This is most noticeable over Antarctica. To stop the damage to the ozone layer, the United Nations Environment Programme (UNEP) brought forward an agreement in 1987 to freeze the CFC production at the 1986 level. Most countries have signed this agreement. As a result, there has been a slight decrease in the rate of depletion of the ozone layer. • POINTS TO REMEMBER • ·

An ecosystem is a functional unit consisting of all the living beings of an area and the nonliving components of their environment, interacting to form a stable system.

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An ecosystem consists of abiotic (nonliving) and biotic (living) components. The biotic component includes plants and animals, whereas the abiotic component includes the physical environment, nutrients and climatic factors.

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Organisms which make their own food are called producers or autotrophs. Green plants and certain blue-green algae are producers. Organisms that depend on other organisms for food are called consumers or heterotrophs. Consumers can be classified as herbivores (plant-eaters), carnivores (flesh-eaters) and omnivores (eat both plants and flesh). Organisms which feed on dead plants and animals are called decomposers. Decomposers include bacteria, fungi and worms.

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A food chain in an ecosystem is a series of organisms in which each organism feeds on the one below it in the series. A level or position in a food chain is called a trophic level.

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A food web is a series of interconnected food chains representing the feeding relationship of the organisms within an ecosystem. For an ecosystem to work, there has to be a flow of energy and a cycling of nutrients. The flow of energy is unidirectional, from a lower to a higher trophic level. Only about 10% of the energy available to a trophic level is transferred to the next higher level. The progressive increase in the accumulation of a harmful substance in organisms at successively higher trophic levels is called biological magnification or biomagnification. Materials that get broken down by living organisms are called biodegradable materials. These are substances of plant or animal origin. Materials that cannot be broken down by living organisms are called nonbiodegradable materials, e.g., metals, plastics, DDT. Nonbiodegradable materials are major pollutants. Chemicals like CFCs have damaged the protective ozone layer, which absorbs the harmful ultraviolet radiation.

• EXERCISES • A. Very-Short-Answer Questions 1. What is an ecosystem? 2. Categorize these as primary, secondary and tertiary consumers: grasshopper, snake, hawk, owl, rat and rabbit. 3. Give a scientific term for each of the following. (a) The green plants which synthesize food (b) Organisms which feed on plants or plant products (c) Organisms that can convert dead and decaying organic matter into simpler form

9. One hundred kilocalories of energy are available to a trophic level. Approximately how much energy can be transferred to the next higher trophic level? 10. Food chains usually do not have more than four trophic levels. Why? 11. What is the main difference between biodegradable [CBSE] and nonbiodegradable wastes? 12. Name one category of chemicals that are responsible for the ozone hole. B. Short-Answer Questions

4. What is a food chain?

1. What are the components of an ecosystem?

5. Give one example of a simple food chain.

2. How are heterotrophs different from autotrophs?

6. Which category of organisms forms the starting point of a food chain?

3. What is the importance of decomposers in an ecosystem?

7. Make a flow chart of a food chain commonly found on land.

4. Why do you need to clean an aquarium periodically while ponds do not need to be cleaned?

8. Define food web.

5. What do you understand by a trophic level?

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6. What will happen if all the organisms at a trophic level die?

6. In a food chain, herbivores constitute the (a) first trophic level (b) second trophic level (c) third trophic level (d) fourth trophic level

8. Usually, why do you have a greater number of organisms at the lower trophic levels? 9. Construct a food web that has rabbits, plants, herbivorous insects, hawks, sparrows, wolves, spiders, frogs and snakes. 10. Where is the ozone layer found? What is the importance of ozone layer? [CBSE]

7. Which of the following constitute a food chain? (a) Plant, apple, butterfly, man (b) Grass, spider, bee, buffalo (c) Plant, insect, toad, snake (d) Algae, insect larvae, fish, cow

11. How is ozone formed in the upper atmosphere? Why is damage to the ozone layer a cause of concern to us. What causes this damage? [CBSE] 12. What are the problems caused by nonbiodegradable wastes?

8. What happens in biological magnification? (a) There is progressive increase in the level of harmful substances through trophic levels. (b) There is a progressive increase in the body weight through trophic levels. (c) There is a progressive increase in the number of organisms through trophic levels. (d) There is progressive increase in biological activities through trophic levels.

C. Long-Answer Questions 1. All heterotrophs are consumers. How would you classify them? 2. Explain the flow and loss of energy in an ecosystem. 3. What is biological magnification? Explain how the level of accumulation of harmful substances varies with trophic levels.

9. The flow of energy in an ecosystem is (a) unidirectional (b) bidirectional (c) multidirectional (d) cyclic

4. What is the ozone hole? How was it formed? What is being done to control it?

D. Objective Questions

10. Which of the following contain nonbiodegradable things? (a) Leaves, wood, plastics (b) Polythene, aluminium can, mercury (c) DDT, cow dung, fruit peels (d) Kitchen waste, sewage, pen

I. Pick the correct option. 1. In an ecosystem, there is a flow of (a) energy only (b) nutrients only (c) water only (d) energy and nutrients 2. The ultimate source of energy in an ecosystem is the (a) producer (b) consumer (c) sun (d) decomposer

4. Out of the following, which is a linear arrangement of organisms? (a) Trophic level (b) Ecosystem (c) Food chain (d) Food web

• ANSWERS • Objective Questions 3. (c) 8. (a)

4. (c) 9. (a)

only

II. Fill in the blanks. 1. The physical and biological conditions in which an organism lives is its _____. 2. In a food chain, each position is known as a _____ level. 3. Those who feed directly on the producers in an ecosystem are called _____ consumers. 4. All green plants are _____ , whereas animals are consumers. 5. If the energy available at a trophic level is 100 units, the energy available at the level just below it will be about _____ units. 6. The ozone layer protects us from _____ radiation.

3. The biotic component of an ecosystem consists of (a) plants and animals (b) green plants and algae (c) producers, consumers and decomposers (d) air, water and soil

2. (c) 7. (c)

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5. The third trophic level of a grassland food chain can have (a) grass (b) grasshoppers (c) hawks (d) frogs

7. In what direction does the energy flow in a food chain? Why is it unidirectional?

1. (d) 6. (b)

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5. (d) 10. (b)

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1. PREPARATION OF TEMPORARY MOUNTS Experiment 1.1 Objective To prepare a stained temporary mount of an onion peel and to record observations and draw labelled diagrams Apparatus and materials required An onion, glass slide, watch glass, coverslip, forceps, needles, brush, blade, filter paper, safranin, glycerine, dropper, water, and a compound microscope Theory All living organisms are made up of cells. The shape, size and the number of these units vary in organisms. The three major components of a cell are the cell membrane, cytoplasm and nucleus. In a plant cell, a cell wall surrounds the cell membrane. Procedure 1. Take an onion and remove its outermost peel. 2. Now cut a small part from an inner scale leaf with the help of a blade. 3. Separate a thin, transparent peel from the convex surface of the scale leaf with the help of forceps. 4. Keep this peel in a watch glass containing water. 5. Add two drops of safranin stain in the watch glass to stain the peel. 6. Take a clean slide and put a drop of glycerine in the centre of the slide. 7. With the help of a brush and needle transfer the peel on the slide. Glycerine prevents the peel from drying up. 8. Carefully cover it with a coverslip and avoid any air bubble from entering under the coverslip. 9. Remove any excessive glycerine with a filter paper. 10. Observe the prepared mount of the peel under the low and high magnification of a compound microscope. Observations A large number of rectangular cells are visible. These cells lie close to each other with intercellular spaces between them. These cells are surrounded by distinct cell walls. These cells have a dark stained nucleus and a large vacuole in the centre. 94

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Fig. 9.1 (a)–(b) Methods of separating an onion peel (c) Structure of onion cells as seen under a microscope (450 ´)

Precautions 1. Overstaining and understaining should be avoided. 2. Folding of the peel should be avoided. 3. Clean and dry glass slide and coverslip should be used. 4. Coverslip should be put carefully avoiding any air bubbles.

Experiment 1.2 Objective To prepare a stained temporary mount of human cheek cells and to record observations and draw labelled diagrams Apparatus and materials required Toothpick, slide, coverslip, filter paper, needles, brush, watch glass, methylene blue, dropper, glycerine, water and a compound microscope Theory Animal cells are usually irregular in shape. They do not have a cell wall. They are surrounded by a cell membrane and contain cytoplasm and nucleus. Procedure 1. With the help of the flat end of a washed toothpick gently scrape the inside of your cheek. 2. Place the scrapings in the centre of a clean glass slide.

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3. Add a drop of water and a drop of methylene blue. 4. After one minute remove the extra water mixed with methylene blue by slightly tilting the slide. 5. Put a drop of glycerine over the stained scrapings and cover it gently with a coverslip. 6. Remove the excessive glycerine using filter paper. 7. Observe the scrapings under the low and high magnifications of a microscope. Observations Many flat, oval or irregular cells are seen. The cell membrane encloses hyaline cytoplasm and an oval, dense nucleus. The cell wall is absent as in all animal cells.

(b) Cheeck cells as seen under a microscape

Fig. 9.2 (a) Removing epithelial cells from

the buccal cavity using a toothpick

Precautions 1. The cheeks should be scraped gently avoiding any injury. 2. Overstaining and understaining of the cells should be avoided. 3. Coverslip should be placed carefully avoiding the entry of air bubbles. 4. A dry and clean glass slide and coverslip should be used. 5. The cheek cells should be spread properly to avoid their folding.

VIVA VOCE 1. Why are plant cells regular in shape? Plant cells are regular as they are surrounded by a thick and rigid cell wall. 2. Why do we use glycerine for mounting onion peel or cheek cells? We use glycerine as it does not allow the onion peel or the cheek cells to dry quickly. 3. Why can’t we see mitochondria and other cytoplasmic organelles in the cells of the mount?

It is because we observe it under a light microscope with low magnification and low resolution. The higher magnification of an electron microscope and proper staining are required to observe mitochondria and other cytoplasmic organelles in the cell. 4. What are the three main parts of a cell? The three main parts of a cell are membrane, cytoplasm and nucleus. 5. What is the visible difference between an onion peel cell and a cheek cell? An onion peel cell has a thick cell wall, while a human cheek cell does not have cell wall. 6. Which stain is used for staining plant cells? Safranin.

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7. Name the stain used for staining animal cells.

Methylene blue. 8. What is the main constituent of cell walls?

Cellulose.

2. TISSUES Experiment 2.1 Objective To identify parenchyma and sclerenchyma tissues in plants from prepared slides and to draw their labelled diagrams Apparatus and materials required Permanent slides of parenchyma, sclerenchyma, and a compound microscope Theory A group of cells of the same size and shape, or of a mixed type, having a common origin and performing an identical function is called tissue. Plant tissues are of two types—meristematic and permanent. Meristematic tissue cells are capable of dividing, while permanent tissue cells are not. Parenchyma, collenchyma, and sclerenchyma are the three types of simple permanent tissues. Procedure 1. Take a permanent slide of parenchyma and study under the low magnification and then under the high magnification of microscope. 2. Similarly place and study the other permanent slides of sclerenchyma. Observations The first slide of parenchymatous cells reveals the following features. Characters of Parenchyma 1. The cells are generally oval or spherical in shape. 2. These cells are large and are not packed closely, i.e., intercellular spaces are present. 3. Each cell has a large central vacuole and a peripheral cytoplasm with a prominent nucleus. 4. These living cells are found in the soft parts of the plants, i.e., root, stem, leaves, flowers, and fruits. 5. The important functions of these cells are storage of food, filling up spaces between other tissues and providing support to the plant. When they contain chloroplasts as in leaves, they help in the synthesis of food. The slides of sclerenchymatous cells show the following identifying features. Characters of Sclerenchyma 1. Cells are thick-walled, hard and contain little or no protoplasm. 2. The cells are oval, polygonal and are of different shapes. 3. The cells are dead and the nucleus is absent. 4. These cells are packed closely, i.e., intercellular spaces are absent. 5. The cell wall is evenly thickened with lignin and perforated with pits. 6. They provide strength and rigidity to the plant parts with hardness.

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Fig. 9.3 Types of simple permanent tissues (a) Parenchyma cells in transverse section (b) Parenchyma cells in

longitudinal section (c) Sclerenchyma cells in TS (d) Sclerenchyma cells in LS

Experiment 2.2 Objective A. To examine the prepared slide of striped muscle fibres

Observations You will find that the cells are cylindrical. The location of the nucleus is interesting, it is not in the centre of the cylinder. The nucleus may be seen just near the outside of the cell. When you examine the cytoplasm carefully, you will find striations arranged in a parallel fashion.

Fig. 9.4 Striated or voluntary muscle fibre (a) Isolated skeletal fibre (b) Fibre details

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Objective B. To examine the prepared slide of nerve cells.

Observations When you focus on an individual nerve cell, you will see a buldging part which is called cyton. In the centre of the cyton you will find a nucleus. If the material was specially prepared, you may be able to locate granules around the nucleus. Try to count the number of processes arising from the cyton. The smaller processes arising from the cyton look like roots and are called dendrites. A long, cylindrical process arising from the other side of the cyton is called an axon. It ends in a bulb called axon bulb.

Fig. 9.5 Structure of a nerve cell

VIVA VOCE 1. Define tissue. A tissue is a group of cells with similar structure organised to do a common function. 2. What is the difference between meristematic and permanent tissue? Meristematic tissue cells are capable of dividing, while permanent tissue cells are not. 3. Name the plant parts where parenchymatous cells are present. Parenchymatous cells are present in the soft parts of root, stem, leaves, flowers and fruits. 4. What are the examples of simple permanent tissue? Parenchyma, collenchyma, and sclerenchyma. 5. Name the plant tissue which is dead at maturity. Sclerenchyma. 6. Name the plant tissue which is mainly responsible for mechanical strength. Sclerenchyma. 7. Why are the sclerenchymatous cells hard? They are hard because their cell wall is thickened with lignin. 8. In which tissue is the cell wall perforated with pits? Sclerenchyma.

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3. CHEMICAL ANALYSIS OF FOODSTUFFS AND THEIR ADULTERANTS Experiment 3.1 Objective To test the presence of starch in the given food sample Apparatus and materials required Test tubes, test-tube stand, test-tube holder, spirit lamp, dropper, filter paper, iodine solution, distilled water, and foodstuff (potato, rice, wheat or maize grains) Theory Starch, a complex carbohydrate, is composed of 15%–20% amylose and 80%–85% amylopectin. It is found in different kinds of cereals such as rice, wheat, maize, etc. After reacting with iodine solution starch forms a dark, blue-black compound. The appearance of blue-black colour is due to the presence of amylose in starch.

Test tube

Filtrate + 2 drops of iodine solution

Procedure 1. Take a few small, freshly cut pieces of potato or a few grains of rice or wheat or maize in a clean test tube.

Blue-black colour

Fig. 9.6 Test for the presence of

starch in foodstuff

2. Pour 10 mL distilled water into the test tube. 3. Now, boil the contents of the test tube for about 5 minutes. 4. Allow the test tube to cool. 5. Filter the contents of the test tube through a filter paper. 6. Test the obtained filtrate for the presence of starch by the following method. Observation Experiment

Take 2 mL filtrate in a clean test tube. Add 2 drops of iodine solution to it by a dropper.

Observation

The colour of the filtrate changes to dark blue-black.

Inference

Appearance of dark blue-black colour shows the presence of starch.

Precautions 1. Use test-tube holder for holding the test tubes and keep the mouth of the test tube away from yourself while heating. 2. Use clean test tubes. 3. Do not use too much of iodine solution.

Experiment 3.2 Objective To test the presence of the adulterant metanil yellow in dal (pulse) Apparatus and materials required Test tubes, test-tube stand, test-tube holder, conc. HCl, mortar-pestle, filter paper, distilled water and a sample of dal

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Theory Metanil is a cheap dye which is commonly used in colouring non-food items like clothes. Government of India has introduced “Prevention of Food Adulteration Act” to prevent the use of harmful chemicals such as this dye in foodstuffs. Procedure 1. Grind 3–5 g of dal in a mortar-pestle. 2. Take this powdered dal in a clean test tube. 3. Pour 10 mL distilled water into the test tube and shake it well. 4. Filter the contents of the test tube through a filter paper and use the filtrate to test for metanil yellow by the following method.

Fig. 9.7 Test for the presence of metanil

yellow in pulse (dal) sample

Observation Experiment

Take 2 mL filtrate in a clean test tube. Add 2 drops of conc. HCl to it with the help of a dropper.

Observation

Yellow colour of the mixture changes to pink.

Inference

The change in the colour from yellow to pink shows the presence of metanil yellow.

Precautions 1. Always use clean test tubes. 2. Use test-tube holder at the time of adding conc. HCl and keep the mouth of the test tube away from yourself. 3. Do not add excess conc. HCl. 4. Handle the bottle of conc. HCl carefully.

VIVA VOCE 1. What are the major components of food?

Carbohydrates, proteins and fats are the major components of food. 2. What is starch?

Starch is a polymer of glucose and is a complex carbohydrate. 3. What are food adulterants?

Cheap and inferior materials mixed with foodstuff are called food adulterants. 4. In which form is carbohydrate stored in plants?

Starch 5. Name some good sources of starch.

Potato, rice, wheat and maize 6. What harm can be caused by food adulteration?

Several diseases in human beings, and even death may be caused by consuming adulterated food. 7. Name some common sources of protein.

Pulses, eggs and milk 8. In which form is carbohydrate stored in animals?

Glycogen 9. Name the disease caused by eating arhar dal adulterated with khesari dal.

Lathyrism 10. Most food items are marked with ISI, FPO and Agmarks. What are their full forms?

ISI–Indian Standard Institute, FPO–Food Products Order, and Agmarks—Agricultural Marketing

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4. TRANSPORTATION IN PLANTS—ENDOSMOSIS IN RAISINS Experiment Objective To determine the percentage of water absorbed by raisins Apparatus and materials required A bowl, forceps, a common balance, a weight box, blotting paper and a few raisins Theory When raisins are placed in water (a hypotonic solution), they absorb water by a process called osmosis and swell up. Osmosis is the net movement of solvent molecules from a region of their higher concentration to a region of their lower concentration through a semipermeable membrane. The movement of water into the cells of the raisins through their cell membranes continues until the cells become turgid. This process is called endosmosis. If these swollen raisins are now kept in a concentrated salt or sugar solution (a hypertonic solution), water from the turgid raisins will come out of the cells and they will shrink. This process is called exosmosis. The percentage of water absorbed by the raisins due to endosmosis can be measured by knowing the difference of their initial weight and final weight.

Procedure 1. 2. 3. 4.

Take three raisins and weigh them on the common balance. Let this value be W1 . Keep these raisins in a bowl containing water for 2 hours. Take the raisins out of water and gently dry them with the help of blotting paper. Weigh the soaked swollen raisins again on the common balance. Let this value be W2 .

Fig. 9.8 Experiment to show endosmosis

Observations 1. Weight of dry raisins = W1 . 2. Weight of swollen raisins = W2 . 3. Weight of the water absorbed by raisins = W2 - W1 . 4. Percentage (%) of water absorbed by raisins = Result

W2 - W1 W1

´ 100.

The soaked swollen raisins weigh more than the dry raisins. This is because the raisins absorbed water by the process of endosmosis. Precautions 1. The raisins should be weighed accurately.

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2. The raisins should be immersed completely in water. 3. Before weighing the soaked raisins, these should be dried gently with the help of blotting paper.

VIVA VOCE 1. Define osmosis. The net movement of solvent molecules from a region of their higher concentration to a region of their lower concentration through a semipermeable membrane is called osmosis. 2. By which process do water molecules diffuse out from a living cell? Exosmosis 3. Which molecules can move freely across the semipermeable membrane of plant cells? Water molecules 4. How long does endosmosis continue? Endosmosis continues until the concentration of water molecules becomes equal inside and outside the cell. 5. What is endosmosis? The movement of water into the cell across a semipermeable membrane is called endosmosis. 6. Why should we dry the raisins with blotting paper gently after taking them out of water? Any extra water present on the outer surface of the raisins will increase the final weight and give an incorrect result. 7. What is a hypotonic solution? A solution in which the concentration of solute molecules is less than the concentration of solute molecules in a cell sap is called a hypotonic solution. 8. How is osmosis different from diffusion? In osmosis a semipermeable membrane is present between the two solutions, while in diffusion there is no such membrane.

5. DIVERSITY OF PLANTS Experiment Objective To study the characteristics of Spirogyra, Agaricus, Moss, Fern, Pinus (either with male or female cone) and an angiospermic plant. Draw and give two identifying features of the groups they belong to. Apparatus and materials required A slide of Spirogyra, specimen of Agaricus, moss, fern, Pinus with a male female cone, an angiospermic plant, like mustard, hand lens and a compound microscope. Theory Diverse organisms have a wide range of sizes, structures, forms, shapes and distributions on the earth. There are more than 10 million organisms on the earth. About 1.7 million of them (1.2 million animals and 0.5 million plants) have been identified, scientifically named and classified.

Spirogyra (green algae) Characteristics 1. Spirogyra is a green alga having a filamentous, unbranched, multicellular and threadlike structure. 2. Each filament has a large number of rectangular (length being more than breadth) cells. 3. Each cell has two parts: the thick, two-layered cell wall (outer wall made up of pectin and the inner wall is cellulosic) and the protoplasm.

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4. The filaments of Spirogyra are slimy to touch due to the dissolution of their outer pectin layer. 5. The cytoplasm has a large vacuole at the centre and 1–16 ribbon-shaped, spirally coiled chloroplasts. Each chloroplast has a number of small round bodies called pyrenoids. 6. A large nucleus is suspended in the centre of the cell by a number of cytoplasmic strands.

Fig. 9.9 (a) A part of the filament of Spirogyra (b) Detailed structure of a cell

Characteristic features of the group 1. The green algae Spirogyra belongs to the group Thallophyta. The members of this group have an undifferentiated body called thallus. 2. No vascular system is found in the members. 3. Algae are autotrophic, i.e., they synthesize food by photosynthesis as they have the chlorophyll pigments.

Agaricus (mushroom) Characteristics 1. Agaricus is a common, white, fleshy edible mushroom. 2. It grows in the rainy season on damp logs of wood, trunks of trees and decaying organic matter. 3. It is a saprophytic fungus. 4. The body is umbrella-shaped and is divided into a fleshy stalk, or stipe, and a fleshy pileus, or cap. 5. The pileus is dome-shaped, present at the top of stipe. The under surface of the pileus has many radiating strips called gills.

Fig. 9.10 (a) Agaricus (b) Gills in enlarged view

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6. A membranous, ringlike structure called annulus is present on the stalk which covers the young basidiocarp. 7. The function of the basidiocarp is to produce and disperse spores. Characteristic features of the group 1. A mushroom is a fungus that belongs to the group Thallophyta. 2. The modes of nutrition in fungi are saprophytic or parasitic. 3. They do not possess chlorophyll, hence depend either on dead organic matter or on other living organisms for food.

Funaria (moss) Characteristics 1. Mosses are commonly found growing in tufts on moist and shady walls, damp soil and on tree trunks. 2. The main plant body is a gametophyte (haploid) which is green, erect (1–3 cm high) and sparsely branched. 3. The plant body is differentiated into rootlike structures called rhizoids, axis, or stem and spirally arranged leaves. 4. The rhizoids are branched and multicellular which fix the plant to the soil and absorb water and minerals.

Fig. 9.11 (a) Funaria (moss) plant bearing sporophyte (b) External features of a leaf

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5. The plant is monoecious or dioecious, i.e., bear both male and female sex organs on the same plant. 6. The mature plant bears sporophyte which consists of foot, seta and capsule for asexual reproduction. Identifying features of the group 1. Mosses belong to Bryophyta. 2. Proper root and shoot systems are absent. Vascular tissues are absent in this group. 3. Rhizoids present in this group function as roots.

Dryopteris (fern) Characteristics 1. Dryopteris is commonly found in shady and moist areas in tropical, subtropical and warm, temperate regions. 2. The plant body is a sporophyte (diploid) which is differentiated into roots, rhizome (underground stem) and leaves. 3. The primary root is short-lived. It is replaced by adventitious roots which grow from the rhizome. 4. The rhizome represents the modified stem. It is a creeping structure and its surface is covered with leaf bases and numerous thin brown hair called ramenta. 5. The leaves are large and bipinnately compound. The entire leaf is called a frond. It has a rigid, scaly petiole elongated to form a rachis bearing two rows of leaflets. Young leaves show circinate vernation (coiled inwards like a spring). 6. The lower (ventral) surface of mature leaves bear spore-producing structures called sori. Such sori-bearing leaves are called sporophyll. 7. Each sorus has many saclike sporangia (spore-bearing structures), which produce spores.

Fig. 9.12 (a) External features of Dryopteris (fern) (b) Ventral veiw of a pinna-showing sori

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Identifying features of the group 1. Ferns belong to Pteridophyta. 2. The plant body is differentiated into root and shoot systems. 3. Vascular system is present in the members of this group.

Pinus Characteristics 1. Pinus is commonly found on temperate and tropical hills. 2. The adult plant is a tall, evergreen tree with widespread branches giving a typical pyramidal shape. 3. The plant body is differentiated into tap root, stem and leaves. 4. The stem is thick, cylindrical and bears two types of branches—long shoots, or branches of unlimited growth and dwarf shoots, or branches of limited growth. 5. The leaves are of two types (dimorphic)—scale leaves which are nonphotosynthetic, found at the base of dwarf shoot and foliage leaves which are needle-like, green, photosynthetic, and found on the dwarf shoot. 6. The male and female reproductive parts in the form of male and female cones are present on the same plant, i.e., the plant is monoecious. Male cone (staminate strobilus) 1. The male cones are present in clusters (15–140) on long branches. 2. These are small dark brown, compact, oval structures which develop earlier than the female cones.

Fig. 9.13 Pinus (a) Long and dwarf shoots with male and female cones (b) A part of stem showing two types of leaves

and branches (c) Cluster of male cones (d) Female cone in different stages

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3. Each male cone has a centrally located cone axis with many microsporophylls (space-producing structures) arranged spirally on it. 4. Each microsporophyll bears two microsporangia, or pollen sac, on its lower surface. 5. The microsporongia release winged-pollen grains which are carried by the wind to ovules. Female cone (ovulate strobilus) 1. The female cones are born in groups of 2–4 at the tips of long branches. 2. They are maroon-coloured, compact and bigger in size than the male cones. 3. Each female cone consists of a central cone axis covered with spirally arranged megasporophylls. 4. Megasporangia in the form of two naked sessile ovules are present on the dorsal surface of each megasporophyll. 5. The female cones take 3 years to mature. The first-year cones are very small and greenish in colour. The second-year cones are larger and woody with compact sporophylls which get separated during the third year due to elongation of the cone axis. Identifying features of the group 1. Pinus is a Gymnosperm. 2. The plant body has root and shoot systems with vascular tissues, but flowers are absent. 3. The members of this group bear naked seeds on the scales of cones.

A dicotyledonous Angiosperm (mustard) Characteristics 1. The plant is an annual herb.

Fig. 9.14 Brassica campestris (mustard). (a) A flowering plant (b) A fruit-showing seeds

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2. 3. 4. 5.

The plant body consists of the vascular shoot and root systems. The root is a tap root. The shoot system consists of stem, leaves, flowers and fruits. The stem is green, erect, herbaceous, branched, solid and smooth, bearing prominent nodes and internodes. 6. The leaves are sessile, alternate and dorsiventral with lobed margin. 7. The flowers are yellow, tetramerous (4 petals and 4 sepals) and bisexual. All the four whorls of a flower, i.e., calyx, corolla, androecium (male) and gynoecium (female) are present. 8. After fertilization ovary of the flower develops into a fruit and the ovules present inside the ovary develop into seeds. The seeds are used for extracting mustard oil. Identifying features of the group 1. The angiospermic plants have well-developed root system and shoot system. 2. The plants bear flowers, fruits and seeds. 3. These plants are either monocotyledonous (seeds with one cotyledon) or dicotyledonous (seeds with two cotyledons). Monocots have leaves with a scattered arrangement of vascular bundles. Dicots have reticulate venation in leaves and their vascular bundles are arranged in ring.

VIVA VOCE 1. What are algae?

Algae are chlorophyll-bearing thallophytes which are usually aquatic. 2. What are thallophytes? The plants which are not differentiated into roots, stems and leaves, and are without vascular tissues are called thallophytes. 3. If an alga is devoid of chlorophyll, would you call it a fungus? No, there are certain algae which lack chlorophyll and are parasitic in nature. 4. What is the role of pyrenoids present in the chloroplast?

Pyrenoids store starch and proteins of the cell. 5. Why is the Spirogyra commonly known as pond silk? The filaments of Spirogyra are slimy and silklike in texture. 6. What makes the Spirogyra filaments slimy to touch? The outer cell wall of Spirogyra is made of pectin which dissolves in water and forms a slimy mucilaginous envelope around the filament. 7. What is the most characteristic feature of Spirogyra? It has ribbon-shaped, spirally arranged chloroplasts. 8. Why are fungi heterotrophic? Fungi are heterotrophic because they obtain their food either from dead organic matter (saprophytes) or from living organisms. 9. What is the botanical name of edible mushroom? Agaricus campestris. 10. Can you grow mushrooms in your house? Yes, they can be grown in wooden trays containing decaying organic matter. 11. Why are mushrooms called saprophytes? Because they derive food from dead and decaying organic matter. 12. How do fungi differ from algae?

Algae are autotrophic and have a cell wall made of cellulose, while fungi are heterotrophic and have cell wall made of chitin.

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13. What are bryophytes?

Bryophytes are nonvascular, thalloid, autotrophic plants with multicellular sex organs surrounded by a sterile jacket. 14. What is the dominant phase in Funaria? The gametophytic phase. 15. What type of leaves do you find in mosses? Small, sessile and spirally arranged on the stem. 16. What are sporophylls? Sporophylls are vegetative leaves bearing sporangia. 17. What is circinate vernation?

Young leaves of Pinus remain coiled like a spring and open slowly from the base upwards as they mature. This is called circinate vernation. 18. How are pteridophytes different from bryophytes? A pteridophyte is differentiated into root, stem, leaves, has vascular tissues (xylem and phloem), and the sporophyte is independent. All these are absent in bryophytes. 19. What are gymnosperms? Gymnosperms are a group of plants with naked ovules (not enclosed in ovary) and naked seeds. 20. How many types of branches are found in Pinus? Two types of branches—long shoots and dwarf shoots. 21. Where are the foliage leaves found in Pinus? On the dwarf shoots. 22. What is a male cone?

It is a compact aggregation of several microsporophylls bearing microsporangia. 23. In how many years does the female cone of Pinus mature? In 3 years. 24. What characters of Pinus classify it as a gymnosperm? The ovules in Pinus are exposed. After fertilization they develop into naked seeds. Reproductive organs remain in the form of male and female cones. Due to these characters Pinus is classified as a gymnosperm. 25. What are angiosperms? All flower-bearing plants are called angiosperms. 26. How will you define a flower? A flower may be defined as a modified shoot which is meant essentially for the reproduction of the plant. 27. Which group of angiosperms has reticulate venation in leaves and vascular bundles arranged in a ring? Dicots. 28. What are the characteristic features of monocots? Parallel venation in leaves, scattered vascular bundles in stem and trimerous flowers (floral whorls in groups of 3) are the characteristic features of monocots.

6. ADAPTATION IN ANIMALS Experiment Objective Observe and draw the specimens of earthworm, cockroach, bony fish and bird showing a specific feature and an adaptive feature

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1. Earthworm Examine the body of an earthworm. It is cylindrical. The body is divided into a number of segments. It has no other appendages. The anterior half has a band of skin called clitellum. A fresh specimen will be moist. The shape of the earthworm makes it a suitable burrower of the soil. Mouth

Setae

Female genital aperture Clitellum

Male genital pore Anus

Genital papillae Annuli Prostomium Peristomium

Setae

(a)

(b)

Fig. 9.15 Pheretima posthuma (earthworm). (a) Ventral view of

the entire worm (b) Dorsal view of the anterior end

2. Cockroach Examine the body of a cockroach. You will find that it has 6 legs. Each leg has joints. A cockroach has two compound eyes. At the posterior end it has two anal cerci. The body is dorsoventrally flattened and is divided into 3 parts: head, thorax, and abdomen. The jointed legs make it a runner and its wings enable it to fly for a short distance. Note that the outer wings are leathery, but the inner ones are thin and membranous.

Fig. 9.16 Periplaneta americana (cockroach) (a) Dorsal view of male (b) Ventral view of female

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3. Bony fish Examine a bony fish. Note the position of the eyes, shape of the mouth, scales on the body, fins on the dorsal and ventral surfaces. Also examine the shape of the tail fin. You can also feel the endoskeleton by grabbing it firmly. The contour of the body is streamlined so that it can swim without much resistance. Fins also help in swimming. The gills are located just behind the head on the lateral sides. The gills are covered by an operculum. Gills enable the fish to obtain oxygen dissolved in water, and expel the carbon dioxide produced in the body.

Fig. 9.17 Labeo rohita

4. Bird Examine a pigeon. Observe the position of the beak. See the types of plumage, forelegs and wings. Hindlegs have claws. Try to look for teeth in the jaws. You will find none. There are scales in the hindlegs. The body is light. The body plan of the bird helps it to fly long distances. Hold the bird gently with your hands. You will feel that its body temperature is higher than yours.

Fig. 9.18 Columba livia (pigeon)

7. EXTERNAL FEATURES OF PLANT PARTS Experiment Objective To study the external features of root, stem, leaf and flower of monocot and dicot plants

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Apparatus and materials required Glass slides, forceps, hand lens, scissors, dissecting microscope, a complete monocot plant such as onion or paddy or wheat or maize, and a complete dicot plant such as mustard or sunflower or pea Theory The flowering plants, or angiosperms, are differentiated into root, stem, leaves and flowers. They bear seeds enclosed in a fruit. They are divided into monocotyledons and dicotyledons on the basis of the kind of seeds they bear. Monocotyledons bear seeds which have a single cotyledon. The seeds of dicotyledons have two cotyledons. Procedure 1. Take a monocot plant. Separate root, stem, a leaf and a flower of this plant with the help of scissors and place these parts on different slides separately with forceps. 2. Then take a dicot plant and repeat the process. 3. Now observe and compare the external features of root, stem, a leaf and a flower of the monocot and dicot plants using hand lens and subsequently by dissecting microscope.

Observation Root Identifying features of root 1. 2. 3. 4. 5. 6. 7. 8.

The part of a plant that generally develops from the radicle of embryo is called root. It fixes the plant firmly into the ground and provides rigidity against wind and water. It absorbs water and minerals from soil. It grows towards the centre of gravity, i.e., it is positively geotropic. It possesses unicellular root hairs. It normally grows away from light, i.e., it is negatively phototropic. It does not bear buds, leaves and flowers, and lacks nodes and internodes. The root has four regions from the apex to the base: (i) Root cap (ii) Region of cell division (apical meristem) (iii) Region of elongation (iv) Region of maturation

Fig. 9.19 Regions of the root

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9. The root cap protects the growing root apex while the main growing region of the root lies just behind the root cap. Monocot Root 1. In monocots, primary root does not persist for a longer period. It is soon replaced by a cluster of long, threadlike roots which originate from the base of the stem. These roots are called fibrous roots. 2. Roots developing from any other part of the plant than radicle are called adventitious roots. 3. Fibrous root is a type of adventitious root. 4. Due to absence of secondary growth in thickness these roots remain slender.

Fig. 9.20 Types of root (a) Monocot root (b) Dicot root

Dicot Root 1. In most of the dicots, root develops directly from the radicle. 2. It grows longer, thickens and is known as primary root. 3. It persists and becomes stronger to form tap root. 4. It generally produces lateral branches called secondary roots. 5. Branches of the secondary roots are called tertiary roots. 6. Tap root along with its branch system is called tap root system.

Stem Identifying features of stem 1. The part of the plant that develops from the plumule of embryo is called stem. 2. It forms the axis and is the ascending part of the plant. 3. It is differentiated into nodes and internodes. 4. It bears leaves and branches at the nodes. The part of stem that lies between two nodes is called internode. 5. It is positively phototropic, i.e., grows towards light and negatively geotropic, i.e., grows away from the gravity. 6. The shoot (stem and its branches) is usually green and photosynthetic. 7. The apex of stem is called shoot tip. It bears apical bud which is responsible for elongation of the plant. Shoot apex lacks cap. 8. Stem bears either unicellular or multicellular hair, or trichomes.

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9. The main function of the stem is to support leaves and branches and hold them in a position to receive maximum light. Thus it forms the main skeleton of the plant. Monocot Stem 1. It is aerial, erect, herbaceous or woody, usually unbranched. 2. It is usually differentiated into solid nodes and hollow internodes. In maize, internodes are also solid. 3. In some members stem is modified into underground organs like rhizome (e.g., ginger), corm (e.g., Colocasia) or bulb (e.g., onion).

Fig. 9.21 External features of plants (a) A monocot plant (onion) (b) A dicot plant (mustard)

Dicot Stem 1. It is normally long, erect, herbaceous or woody, cylindrical and branched. 2. It has distinct nodes and internodes. Both the nodes and internodes are solid. 3. Sometimes it is creeping and modified into tendril. 4. It is often four-angled (quadrangular) or five-angled (pentangular). 5. In potato, the underground stem is modified into tubers.

Leaf Identifying features of leaf 1. It is the lateral appendage of the stem that arises at the node. 2. It bears a bud in its axil. 3. It is attached to the stem with the help of a structure called the leaf base. 4. A stalk called petiole develops from the leaf base which bears a green flattened structure called lamina. 5. Lamina, or leaf blade, has midrib, veins, leaf apex and leaf margin.

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6. The leaves are grouped into two categories—simple and compound—on the basis of incision. Simple leaves have a single lamina. When the incision of the lamina goes down to the midrib, the leaf becomes compound having a number of leaf segments called leaflets. 7. The main functions of leaves are synthesis of food (photosynthesis), transpiration, and exchange of gases through its pores called stomata. 8. Sometimes leaves get modified for storage, defence, support, reproduction and trapping insects. Monocot leaf 1. Leaves are arranged isobilaterally, i.e., both surfaces are similar. 2. The venation (arrangement of veins and veinlets on the lamina) is parallel. In monocots veins run parallel to each other from base to the tip of the lamina. Veinlets connecting the adjacent longitudinal veins are inconspicuous. 3. Leaves are usually long and narrow, running parallel to the stem. 4. Leaves are mostly simple. 5. Leaf sheath (expansion of leaf base into a broad sheath) is usually present. Dicot Leaf

Fig. 9.22 Venation in leaves (a) Reticulate (b) Parallel

1. Leaves are arranged dorsiventrally, i.e., upper and lower surfaces are distinctly different. 2. In dicot leaves, venation is reticulate, i.e., irregularly distributed to form a network. 3. In most dicots, the leaf base bears two lateral appendages called stipules. 4. Leaves are either simple or pinnately compound. 5. Leaf sheath is usually absent.

Flower Identifying features of flower 1. The reproductive part of an angiospermic (higher) plant is flower, which develops from floral buds. 2. The flower is considered to be a modified shoot. 3. The stalk of the flower is called pedicel and the tip of the pedicel continues as an enlarged axis called thalamus or receptacle. 4. All the floral parts are arranged on the thalamus in a definite sequence. 5. A typical flower consists of four sets of floral parts, or whorls: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels). 6. The first two whorls, i.e., calyx and corolla are not directly involved in reproduction and are called accessory whorls. 7. The inner two whorls, i.e., androecium and gynoecium are directly concerned with sexual reproduction and are called essential whorls.

Fig. 9.23 Diagram of different parts of a flower

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8. Sepals form the outermost whorl called calyx. They are usually green and leaflike, and arise at the base of the flower. 9. Petals form the corolla. They are generally brightly coloured and sometimes fragrant to attract insects. 10. The third whorl androecium is the male reproductive part of the flower and consists of stamens. Each stamen consists of a slender filament and an anther at the tip. 11. Gynoecium, or pistil, is the centrally placed fourth whorl which bears the female reproductive organ called carpel. Each pistil consists of a basal swollen ovary, a narrow stalklike style, and stigma at the tip. The ovary contains one or many ovules. Monocot Flower 1. Calyx and corolla are not distinct in monocot flowers. Instead, perianth is present which is composed of tepals. 2. In monocots, flowers appear in clusters. 3. The flower is typically trimerous (each whorl is in multiple of three). 4. Stamens are usually versatile, i.e., filament is attached to the back of anther at a point only. Dicot Flower 1. Dicot flowers usually have distinct floral parts, i.e., calyx, corolla, androecium and gynoecium. 2. Calyx is composed of sepals, and corolla is composed of petals. 3. Flower is mostly pentamerous (each whorl in multiple of five), sometimes tetramerous (each whorl in multiple of four). 4. In dicots, flowers usually appear separately. 5. Stamens are usually basifixed, i.e., filament is attached to the base of the anther.

VIVA VOCE 1. Name the part of the plant which develops from the radicle in dicots. Tap root or primary root 2. Name the structure which protects the root tip. Root cap 3. Which part of the embryo forms the root in a plant? Radicle 4. Why is root said to be positively geotropic? Because it grows towards the centre of gravity. 5. What is the primary function of root? It absorbs water and minerals from the soil. 6. Which type of root is found in monocots? Fibrous root 7. Name the root that develops from any unusual part of the plant body. Adventitious root 8. Name the part of the plant which develops from plumule of embryo. Stem 9. Name the part of the stem that lies between two nodes. Internode

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10. What is the main function of stem? The main function of stem is to support leaves and branches and hold them in a position to receive maximum light. 11. In which type of stem are internodes usually hollow? Monocot stem 12. What is the difference between simple leaf and compound leaf? Simple leaf has single lamina whereas compound leaf has many leaflets. 13. What is the importance of leaves? The leaves help in photosynthesis, transpiration and exchange of gases. 14. What is the difference between monocot leaves and dicot leaves? Monocot leaves are isobilateral having parallel venation while dicot leaves are dorsiventral having reticulate venation. 15. What is venation? The arrangement of veins and veinlets on the lamina is called venation. 16. What is pedicel? The stalk of the flower is called pedicel. 17. Define flower. Flower may be defined as a modified shoot which is essentially meant for reproduction of the plant. 18. What are angiosperms? All flower-bearing plants are called angiosperms. 19. Which type of flowers are usually found in monocots and dicots? Trimerous flowers in monocots, and pentamerous flowers in dicots 20. Name the reproductive organs of a flower. Stamen and carpel 21. Name the outermost whorl of a flower. Calyx 22. Where are perianth found? In monocot flowers 23. What is perianth? It is the outer part of monocot flower in which calyx and corolla are not always distinguishable.

8. LIFE CYCLE OF MOSQUITO Experiment Objective To study the life cycle of mosquitoes Apparatus and materials required Specimens of different stages of life of mosquito, compound microscope Theory Mosquitoes are small harmful insects, found everywhere, especially in damp, dark places. They breed in stagnant water. Eggs develop into larvae, larvae into pupa, and pupa develop into imago, or an adult. The different stages are clearly distinguishable.

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In India, Culex and Anopheles are mostly found.

Observation Eggs Collect eggs from stagnant water bodies such as the nearby drain or ditch, and keep them in a wide-mouthed bottle containing some water. Take the eggs by means of a dropper and put them on the glass slide and examine under the compound microscope. Eggs are laid by the female mosquito in the night in stagnant water. Eggs are slightly brown and extremely small. But on taking a closer look they can be identified as rafts composed of cigar-shaped bodies glued together, or free boat-shaped bodies. Cigar-shaped eggs belong to Culex and boat-shaped ones belong to Anopheles. At a time, Culex lays up to 300 eggs, and Anopheles, 100 eggs. Eggs float on the surface of the water. Examine the sample and note the shape and size of the eggs. Draw a sketch of the shape of the eggs and infer whether they belong to Culex or Anopheles. After 2–3 days, you will notice that these eggs are ruptured, and from each one of them an elongated creature emerges. This is called larva.

(a)

(b)

Fig. 9.24 Eggs of (a) Culex and (b) Anopheles

Larvae Larvae are elongated, hairy, segmented creatures that move about and feed upon algae growing in water. They swim (wriggle) in a characteristic jerking manner and hence they are also called wrigglers. The anterior part of the body has somewhat indistinct head equipped with mouth parts, compound eyes, and antennae. The body is divided into ten segments. Each segment has a few bristles, or hairs. The posterior part of the larva bears gills, respiratory siphons, and the comb. Examine the larvae under the compound microscope to observe the movement of the jaws and the body. You can count the number of segments in the body and observe gills and siphons located at the posterior end. Draw a sketch of a larva. Brush Brush Antenna Head Compound eye

Antenna Compound eye

Thorax Thorax Bristles Abdomen Abdomen

Comb Respiratory siphon

Tracheal gills (a)

Tracheal gills

(b)

Fig. 9.25 Larvae of (a) Culex and (b) Anopheles

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If you see the water surface of the cylinder or the container in which the larvae are kept, you will find larvae hanging by the air-water interface. The posterior part of the larva is always in contact with the meniscus, as respiratory siphons have to draw atmospheric air for respiration. The gills remain submerged in water to draw dissolved oxygen of water. The larva of Anopheles lies parallel to the water surface. The head of the larva of Culex hangs downward at an angle. Larval life lasts for two weeks during which it casts its skin four times. After that the larva is transformed into another form called pupa. Pupae Pupal life is sluggish. There is no feeding, no movement except for occasional tumbling in water. That is why a pupa is called a tumbler. The head of the pupa is large, formed by the fusion of the head and thorax. Therefore, it is called cephalothorax, which bears on its dorsal surface two respiratory trumpets. Legs and wings, which are in the early stages of formation, lie on the ventrolateral surfaces. The pupal life lasts for a week.

Fig. 9.26 Pupae of (a) Culex and (b) Anopheles

Imago (young adult) At the end of pupal life, the skin (cuticle) of the pupa splits along mid-dorsal line, making it easy for the imago to come out. The wings of the newly emerged imago are dried and spread out, and it flies off to lead an aerial life.

Fig. 9.27 (a) Adult Culex (b) Adult Anopheles

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FOR CLASS 10

1. PREPARATION OF TEMPORARY MOUNT Experiment Objective To prepare a temporary mount of a leaf peel to show stomata

Apparatus and Materials Required A potted Tradescantia or Bryophyllum plant, forceps, needles, watch glasses, glass slides, a dropper, coverslips, a brush, blotting paper, safranin, glycerine and a compound microscope

Theory Stomata are small openings found widely scattered on the epidermis of leaves and young stems. They are mostly found on the lower surface of a dicot leaf and on both the surfaces of a monocot leaf. Stomata regulate the exchange of gases and water vapour between the atmosphere and leaves.

Procedure 1. Remove a healthy leaf from the potted plant. 2. Remove a part of the peel from the lower surface of the leaf. You can do this by folding the leaf over and gently pulling the peel apart using forceps. Keep the peel in a watch glass containing water. 3. Put a few drops of safranin stain in a watch glass. 4. After 2–3 minutes take out the peel and place it on a clean glass slide. 5. Put a drop of glycerine over the peel and place a clean coverslip gently over it with the help of a needle. 6. Remove the excess stain and glycerine with the help of blotting paper. 7. Observe the slide under the low-power and high-power magnifications of the compound microscope.

Observations 1. The epidermal cells are visible. These are irregular in outline and have no intercellular spaces. 2. Many small pores (stomata) are seen scattered among the epidermal cells. 3. Each pore is guarded by two bean-shaped guard cells, each containing chloroplasts and a nucleus.

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Fig. 9.28 (a) Mounting a leaf peel (b) Epidermal layer in the peel taken from a dicot leaf

showing open stomata (c) High-power magnification of stomata

4. The inner concave boundary of each guard cell is thick, whereas its outer boundary is thin. 5. The stomata may be open or closed. The guard cells regulate the opening and closing of the stomata.

Result Stomata are present in the epidermal cells of the lower surface of the leaf.

Precautions 1. Cut the peel to a proper size and avoid folding it. 2. Always place the peel at the centre of the slide and hold the slide at the edges. 3. Do not overstain or understain the peel. 4. Always handle the peel with a brush as a needle may damage the cells. 5. Take care to prevent the peel from drying by using glycerine. 6. Place the coverslip gently, avoiding any air bubbles. 7. Remove excess stain and glycerine with a blotting paper.

VIVA VOCE 1. Why do we take an epidermal peel from the lower surface of the leaf? More stomata are present on the lower surface of a dicot leaf than on the upper surface.

2. What are the functions of stomata? Exchange of gases and transpiration

3. Where are stomata located in monocot plants? Stomata are found on both surfaces of the leaves in monocot plants.

4. Which stain is used while preparing a temporary mount of a leaf peel? Safranin

5. Name the cells which surround a stoma. Guard cells

6. How are the opening and closing of stomata regulated? Turgidity of the guard cells regulate the opening and closing of stomata.

7. How do the stomata of dicots and monocots differ? In dicots the guard cells are kidney-shaped, while they are dumb-bell-shaped in monocots.

8. Why are there no stomata in submerged aquatic plants? Submerged aquatic plants remain inside water, and the diffusion of gases occurs through their general body surface.

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9. Why do we use glycerine for mounting a leaf peel? To prevent the cells from drying up

10. How are stomata differentiated from the surrounding epidermal cells? Compared to the epidermal cells, the guard cells are smaller, different in shape and have thicker inner walls.

2. PHOTOSYNTHESIS Experiment Objective To show experimentally that light is essential for photosynthesis

Apparatus and Materials Required A healthy potted plant, a Petri dish, a beaker containing water, forceps, a water bath, a piece of wire gauze, a tripod, a burner, a box of matches, alcohol a strip of black paper, iodine solution and clips.

Theory Photosynthesis is a biochemical process by which green plants synthesize simple sugar in the presence of sunlight using carbon dioxide from the atmosphere and water from the soil. This simple sugar (glucose) is later converted to starch. Chlorophyll

6CO 2 + 12H 2 O ¾ ¾ ¾ ¾ ¾® C 6 H12 O 6 + 6H 2 O+ 6O 2 Sunlight

The most important factor for photosynthesis is light. The rate of photosynthesis depends on the quantity and quality of light. The chlorophyll molecules in green leaves absorb light, get excited and emit electrons. The emitted electrons are used in the production of adenosine triphosphate (ATP). Finally the solar energy is converted into chemical energy and stored in the glucose produced. The rate of photosynthesis is the maximum in the presence of red and blue lights, while in green light the rate is minimum because green light is reflected by the chlorophyll molecules.

Procedure 1. Take the potted plant and keep it in a dark place for 2–3 days so that the leaves get destarched. 2. Cover a part of one of its leaves with the strip of black paper. Make sure that you cover both the sides of the leaf. 3. Now place this plant in sunlight for 3–4 hours. 4. Pluck the selected covered leaf and remove the black paper covering it. 5. Place this leaf in the beaker containing water and boil it for about 10 minutes. 6. Take out the leaf and now boil it in alcohol, using the water bath, for 10 minutes. This removes the chlorophyll. 7. Take out the leaf and wash it under running water. 8. Place this leaf in the Petri dish and put a few drops of iodine solution on it. Now observe the change in colour.

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Fig. 9.29 Experiment to show that light is essential for photosynthesis

Observations The leaf turns blue-black except in the covered region. As this covered region did not receive light, photosynthesis did not occur. Hence no starch was formed there. The uncovered region received light and starch was formed there due to photosynthesis.

Result Light is essential for photosynthesis.

Precautions 1. Before starting the experiment, the leaf must be destarched. 2. The leaf must be covered with black paper properly to prevent the entry of light. 3. Boiling the leaf in alcohol should be done in the water bath.

VIVA VOCE 1. What happens when light falls on chlorophyll molecules? The chlorophyll molecules absorb the light, get excited and emit electrons.

2. What does destarching mean? When green plants are kept in darkness for 2–3 days, photosynthesis does not occur. Sugar is not synthesized and hence not stored as starch. This is called destarching the plants.

3. What are the factors that affect the rate of photosynthesis? Light, carbon dioxide and temperature affect the rate of photosynthesis.

4. Is the rate of photosynthesis same throughout the day? No, the rate of photosynthesis varies with the amount and intensity of light available at different times during the day. 5. What is the source of the oxygen liberated during photosynthesis? Water 6. Why do we use a water bath for boiling the leaf in alcohol? The vapours of alcohol may catch fire if heated directly, without using a water bath.

7. Why is the leaf boiled in alcohol? To remove all the chlorophyll pigments and for decolouring the leaf

8. Which chemical is used to test the presence of starch? Iodine solution 9. Why does the uncovered portion of the leaf turn blue-black after putting iodine solution on

it? The uncovered portion receives light and synthesizes starch by photosynthesis. 10. Why is the rate of photosynthesis reduced considerably in green light? Green light is reflected by the chlorophyll molecules and is not used in photosynthesis.

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3. RESPIRATION Experiment Objective To show experimentally that carbon dioxide is released during respiration

Apparatus and Materials Required A conical flask, a beaker, a cork with a hole, a glass tube bent at right angles at two places, a small test tube, KOH solution, thread, coloured water, Vaseline and germinating seeds of gram or pea

Theory Respiration is a catabolic process which involves the breakdown of food or complex organic molecules into simpler products, with the release of energy. This process can take place either in the presence of oxygen (aerobic respiration) or in its absence (anaerobic respiration). The overall reaction mechanism of aerobic respiration involves the oxidation of carbohydrate and the subsequent production of CO 2 , H 2 O and energy. C 6 H12 O 6 + 6O 2 ¾ ¾® 6CO 2 + 6H 2 O + Energy

Procedure 1. Take the conical flask and place some germinating gram or pea seeds in it. 2. Insert the shorter end of the glass tube through the hole in the cork and fix it on the conical flask. 3. Before fixing the cork, hang a test tube containing KOH solution inside the conical flask with the help of a thread. 4. Take coloured water in the beaker and keep the longer end of the glass tube dipped inside it. 5. Make the conical flask airtight by applying vaseline on its rim. 6. Note the initial level of water in the tube. 7. Observe and note the rise in the water level after an hour, without disturbing the apparatus.

Fig. 9.30 Experiment to show that CO2 is released during respiration

Observations Water level rises up in the bent tube.

Result The rise in the level of water indicates that CO 2 is produced by germinating seeds during respiration. Actually, the germinating seeds respire and produce CO 2 , which is absorbed by KOH solution. This creates a vacuum in the conical flask. The air present in the bent glass tube moves into the conical flask. This pulls the water in the bent tube further up.

Precautions 1. Keep the conical flask airtight. 2. Fix the shorter end of the glass tube in such a way that it does not touch the seeds. 3. Use freshly prepared KOH solution.

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VIVA VOCE 1. Why do we select germinating seeds for studying respiration? Germinating seeds respire actively.

2. Why is KOH solution used in this experiment? KOH solution absorbs the CO2 released during respiration.

3. Why do we use coloured water in this experiment? To record the rise in the level of water in the glass tube correctly

4. What is the difference between a catabolic process and an anabolic process? In a catabolic process complex molecules are broken down into smaller and simpler molecules, while in an anabolic process complex molecules are formed from simpler molecules.

5. Which cell organelle is associated with aerobic respiration? Mitochondrion

6. What are respiratory substrates? The substances oxidized during respiration are called respiratory substrates, e.g., carbohydrates, fats and proteins.

7. Define fermentation. The incomplete anaerobic breakdown of a respiratory substrate with the production of CO2 and energy is called fermentation.

8. Differentiate between aerobic and anaerobic respiration. Aerobic respiration takes place in the presence of O2 and involves the complete oxidation of food, releasing CO2 , H2 O and energy. Anaerobic respiration takes place in the absence of O2 and involves the incomplete oxidation of food, releasing ethyl alcohol and CO2 .

9. What is the difference between the processes of respiration and photosynthesis? Respiration is a catabolic process, whereas photosynthesis is an anabolic process.

10. Which type of respiration releases more energy? Aerobic respiration

11. Which substance is used to make the conical flask airtight? Vaseline (petroleum jelly)

4. ASEXUAL REPRODUCTION—BINARY FISSION AND BUDDING Experiment Objective To study (a) binary fission in Amoeba and (b) budding in yeast with the help of prepared permanent slides

Apparatus and Materials Required Permanent slides of Amoeba showing binary fission and yeast in budding, and a compound microscope

Theory Reproduction is one of the basic characteristics of a living organism. An organism reproduces to produce more of its own kind. Reproduction may be either asexual or sexual.

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The type of reproduction that takes place without gametes forming is called asexual reproduction. Sexual reproduction is the type of reproduction in which both the male and female gametes are involved. Asexual reproduction is common in lower plants and some lower animals. It is a process of rapid multiplication in which the new organisms produced are genetically identical to the parent. Sexual reproduction is common in higher plants and most animals. The organisms produced by this method are not genetically identical to the parents. Asexual reproduction may be of various types such as binary fission, multiple fission, budding, fragmentation, sporulation and vegetative propagation.

Procedure 1. Observe each permanent slide first under the low-power magnification and then under the high-power magnification of a compound microscope. 2. Draw diagrams and compare their features.

Observations Binary fission in Amoeba 1. In this division, two similar individuals are formed from a single parent. 2. A mature Amoeba cell is larger. Its nucleus elongates and gradually divides amitotically into two. 3. The division of the nucleus is followed by the division of the cytoplasm. 4. Thus two new amoebae are formed from a single parent and the parent’s identity is lost.

Fig. 9.31 Binary fission in Amoeba

Budding in yeast 1. In this type of asexual reproduction, bulblike projections called buds arise from the parent body. 2. Mature yeast cells are larger, and spherical or oval in shape.

Fig. 9.32 Budding in yeast

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3. One or more bulblike projections (buds) arise from the cell membrane. 4. The nucleus of the parent cell divides and one of the daughter nuclei passes into the bud. 5. The bud is finally separated from the parent body and grows into a new individual. 6. The parent’s identity is maintained in budding.

Result The prepared slides show asexual reproduction in which only one individual is involved in the production of new individuals.

Precautions 1. Focus the slides properly. 2. Study the slides first under low-power magnification and then under high-power magnification of the compound microscope. 3. Draw diagrams as seen under the microscope.

VIVA VOCE 1. Define binary fission. Binary fission is the division of a single parent cell into two similar daughter cells.

2. What is budding? Budding is a type of asexual reproduction in which a new individual develops within the body wall or from the cell membrane of the parent by forming a bulblike outgrowth, called bud.

3. What is the basic difference between binary fission and budding? In binary fission the parent’s identity is lost, while it is maintained in budding.

4. What are the different modes of reproduction? There are two modes of reproduction—asexual and sexual.

5. What happens during sexual reproduction? In sexual reproduction, the male and female partners produce gametes, which later fuse to form new individuals.

6. Name a multicellular organism that reproduces by budding. Hydra

7. Which organelle divides first during binary fission? Nucleus

8. Name the type of nuclear division that occurs during binary fission. Amitosis

9. By which mode of reproduction are new individuals produced rapidly? Asexual reproduction

10. What type of organism is yeast? Yeast is a unicellular fungus.

5. IDENTIFICATION OF DICOT EMBRYO Experiment Objective To identify the different parts of an embryo of a dicot seed (Pea, gram or red kidney bean)

Apparatus and Materials Required Permanent slides of dicot embryo showing different stages, and a compound microscope

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Theory During sexual reproduction male gamete fuses with female gamete and zygote is formed. After some rest period zygote divides, redivides and finally develops into an embryo. In the earlier stages of development of embryo there is no difference between monocots and dicots, but their development differs in later stages. The process of development of mature embryo from zygote is called embryogeny.

Procedure 1. Observe each permanent slide in sequence from early stages to maturity first under low-power magnification and then under high-power magnification of a compound microscope. 2. Draw diagrams and identify the different parts. 3. Label the different regions of the embryo.

Observation 1. Zygote divides transversely forming a basal cell towards the micropyle and a terminal cell towards the chalaza. 2. The basal cell divides by transverse divisions and finally forms 6–10 celled suspensor. 3. The uppermost cell of suspensor swells up to form a vesicular cell while the lowest cell of the suspensor is called hypophysis. Hypophysis forms part of the radicle and root cap. 4. The terminal embryonal cell divides by transverse and vertical divisions and forms 16-celled globular embryo. 5. The globular embryo later becomes heart-shaped due to its differentiation into cotyledons. 6. The embryo and cotyledons become larger and curved.

Cotyledons Vesicle Stem tip Heart-shaped embryo Suspensor

Root region Suspensor

Suspensor cell Inner integument of ovule Outer integument of ovule

Embryonal cell Hypophysis Globular embryo

Fig. 9.33 Different stages in the development of dicot embryo

Result The prepared permanent slides show successive stages of the development of dicot embryo. The young dicot embryo is globular but changes to heart-shaped structure at maturity due to differentiation into cotyledons.

Precautions 1. Focus the slides properly.

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2. Study the slides first under low-power magnification and then under high-power magnification of the compound microscope. 3. Draw diagrams of the stages as seen under the microscope.

VIVA VOCE 1. What is the term used for the process of development of mature embryo from zygote? Embryogeny

2. Where is vesicular cell present? A vesicular cell is present at the top of the suspensor.

3. What is hypophysis? The lowest cell of the suspensor is called hypophysis.

4. What shape is a young dicot embryo? Globular

5. How many cells are present in suspensor? six to ten cells

6. Which part of the suspensor forms some portion of radicle? Hypophysis

7. Why does globular embryo change to heart-shaped structure on maturity? Due to its differentiation into cotyledons

8. Where is embryo located? Embryo is located inside ovule.

9. How many cells are present in young globular embryo of dicots? Sixteen

10. Is there any difference between the development of dicot and monocot embryo? There is no difference in the development of dicot and monocot embryo during earlier stages but their development differs in later stages.

6. STUDY OF HOMOLOGY AND ANALOGY Experiment Objective To study homology and analogy with the help of preserved specimens of organs of animals

Apparatus and Materials Required Preserved specimens of different organs of animals, compound microscope

Theory In animals, organs that are functionally dissimilar but anatomically, or structurally, similar are called homologous organs. Different modes of life have created the differences, i.e., modified the organs to enable them to survive. Analogous organs are those which are functionally similar but structurally dissimilar.

Observation Homologous organs If you externally examine the wings of the flying mammal bat and the forelimb of a man, you will not find any similarity.

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But examining the bones one by one, you will find that each of them has arm bone (humerus), hand bones (radius-ulna), wrist bones (carpals), palm bones (metacarpals), and fingers (phalanges). Of course, in terms of proportions of growth of each constituent bone, there are differences. For example, the fingers of bat are much longer. What this comparative study suggests is that basically the forelimbs of these two creatures are made up of the same parts, that is, they are anatomically similar. These organs need not perform the same function, as you see that bat uses it for flying and man uses it for handling tools. Hence, the forelimb of man and the wing of bat are homologous organs. Similarly, forearms of cat and man are homologous.

Fig. 9.34 Homologous organs—forelimbs of some mammals

Analogous organs Observe the internal structure of the wings of butterfly, or see its preserved specimen, observe the shape and size. You will find that it is membranous and is made up of thin cuticle. There are veins in the wing but there is no skeleton. Now, take the preserved specimen of a bat and a bird, and examine their wings. You will find skeletal support. What does this type of comparative study indicate? It shows that the basic structures of wings of butterfly, bird and bat are different. In other words, they are anatomically different, although externally they look alike. Wings in these animals are used for flying. Such organs that differ anatomically and in embryonic mode of origin but perform similar function are said to be analogous organs.

Fig. 9.35 Analogous organs—wings

F

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•EXERCISES• FOR CLASS 9 Multiple-Choice Questions

Pick the correct option. 1. What type of cells will you observe in an onion peel examined under a microscope? (a) Dead cells (b) Guard cells and stomata (c) Typical plant cells (d) All of these 2. On adding a drop of iodine solution to an onion peel, (a) the cells will shrink (b) the cells will swell up (c) the cells will turn yellow (d) the food stored as starch in the cells will turn blue-black in colour 3. Why do we cover the onion peel placed on a glass slide with a coverslip? (a) To protect the objective of the microscope (b) To protect the onion peel cells (c) To protect the glass slide (d) To focus the specimen 4. Which type of cells are there in the onion peel? (a) Guard cells (b) Oval cells (c) Epidermal cells (d) None of these 5. An onion is a modified (a) root (c) leaf

(b) stem (d) rhizome

6. When you observe the onion peel under the high magnification of the microscope after observing it under low magnification what differences do you see? (a) Cell size appears larger (b) Fewer cells are seen (c) Cell organelles look magnified (d) All of these 7. Why do we keep the onion peel on a drop of water? (a) To keep the cells living and transparent (b) To prevent displacement of the specimen (c) To make the cells larger (d) None of these 8. What kind of cells are the human cheek cells? (a) Dead animal cells (b) Living animal cells (c) Cells without nucleus (d) All of these 9. Why is the flat end of a sterile toothpick used to scrape the inside surface of the cheek? (a) To prevent injury and infection (b) To get more cells (c) To avoid saliva (d) All of these

10. If the cheek cells are placed on a dirty slide, what do we observe under the microscope? (a) Cells appear coloured (b) Cells show staining (c) Cells are not visible clearly (d) None of these 11. The oval dense structure present in the centre of a cheek cell is (a) cytoplasm (b) cell membrane (c) vacuole (d) nucleus 12. The region between the nucleus and cell membrane in a cheek cell is occupied by (a) protoplasm (b) cytoplasm (c) vacuole (d) none of these 13. Which of the following is not found in cheek cells? (a) Cytoplasm (b) Nucleus (c) Cell membrane (d) Cell wall 14. Which of the following features makes plant cells autotrophic? (a) Plastids (b) Cell walls (c) Lack of centrioles (d) Mitochondria 15. Compared to the onion peel cells, cheek cells are more irregular in shape due to (a) presence of cell membrane (b) lack of large vacuole (c) lack of cell wall (d) lack of plastids 16. In the following figure of a cheek cell which part represents the nucleus? I II III

(a) I (c) III

(b) II (d) None of these

17. Which of the following is an example of simple permanent tissue in plants? (a) Parenchyma (b) Collenchyma (c) Sclerenchyma (d) All of these 18. Which of the following plant tissues generally have oval or spherical and thin-walled cells? (a) Collenchyma (b) Sclerenchyma (c) Parenchyma (d) None of these 19. Which of the following simple permanent tissues does not have closely packed cells? (a) Sclerenchyma (b) Parenchyma (c) Collenchyma (d) All of these

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20. Intercellular spaces are usually found between (a) parenchyma cells (b) collenchyma cells (c) sclerenchyma cells (d) none of these

133

I

(a) I

21. The main functions of parenchyma tissues are (a) storage and assimilation of food (b) providing mechanical strength (c) storage of waste products (d) all of these

II

(b) II

30. A nerve cell is (a) striped (c) syncytial

22. When parenchyma cells contain chlorophyll they are called (a) collenchyma (b) sclerenchyma (c) chlorenchyma (d) none of these

III

IV

(c) III

(d) IV

(b) nonstriped (d) elongated

31. A muscle cell is (a) provided with an end bulb (b) sheathed (c) myelinated (d) contractile

23. Which of the following tissues has lignified cells? (a) Collenchyma (b) Parenchyma (c) Sclerenchyma (d) Chlorenchyma

32. A nerve cell differs from a muscle cell in (a) genetic constitution (b) the kinds of proteins in the cytoplasm (c) being noncontractile (d) the features stated in (b) and (c)

24. Mature sclerenchyma cells are (a) living (b) dead (c) not packed closely (d) thickened with cellulose

33. How many dendrites are there in a hexapolar nerve cell? (a) Five (b) Four (c) Six (d) Seven 34. A solution that has a higher solute concentration than another solution is (a) isotonic (b) hypotonic (c) saturated (d) hypertonic

25. The main function of sclerenchyma is to (a) synthesize food (b) store food (c) give mechanical support (d) store waste products 26. Which tissue is found in abundance fibre-yielding plants like jute and flax? (a) Collenchyma (b) Sclerenchyma (c) Parenchyma (d) All of these

in

27. In the following figure of a nerve cell, which part is an axon? I

II III

(a) I

(b) II

I

II

(b) II

(c) III

III

(c) III

36. A plant cell placed in water will (a) swell up and become turgid (b) swell up and burst (c) lose water and become flaccid (d) shrink and die 37. Raisins placed in water swell up due to (a) plasmolysis (b) adsorption (c) exosmosis (d) endosmosis

IV

(d) IV

28. Which of the following represents the shape of cells lining the intestine?

(a) I

35. When a cell is placed in a hypertonic solution the net movement of water molecules is (a) into the cell (b) out of the cell (c) into the vacuole (d) out of stomata

38. A membrane which allows solvent molecules to pass through it, but not the solute molecules is called (a) impermeable membrane (b) semipermeable membrane (c) permeable membrane (d) none of the above 39. Which of the following is a partially permeable membrane in a cell? (a) Cell wall (b) Cytoplasm (c) Cell membrane (d) All of these

IV

(d) IV

29. Which of the following types of muscle cells constitutes the heart muscle?

40. Endosmosis in a plant cell takes place when it is immersed in (a) an isotonic solution (b) a hypotonic solution (c) a hypertonic solution (d) a saturated solution

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41. In osmosis, the net movement of solvent molecules is (a) from a region of their lower concentration to a region of their higher concentration (b) from a region of their higher concentration to a region of their lower concentration (c) always into the cell (d) always out of the cell

50. Which of the following is the characteristic feature of Spirogyra? (a) Thin cell wall (b) Spiral chloroplast (c) Star-shaped chloroplast (d) Filamentous structure

42. When a raisin is placed in a concentrated sugar solution, it (a) swells up (b) shows no change (c) shrinks (d) dies 43. What is the term used to describe the process in which water from a swollen raisin comes out when the raisin is placed in a concentrated sugar solution? (a) Endosmosis (b) Exosmosis (c) Active transport (d) Reverse osmosis

51. Spirogyra represents (a) multicellular organization (b) filamentous algae (c) photosynthetic aquatic organism (d) all of these

44. A partially permeable membrane of a cell facilitates the process of (a) diffusion (b) plasmolysis (c) osmosis (d) imbibition

52. Spirogyra is commonly known as pond silk due to its (a) filamentous structure (b) silklike texture (c) spiral chloroplast (d) presence in ponds 53. A permanent slide showing green spiral chloroplast like in the following figure, will be of

45. A raisin placed in a concentrated salt solution, shrinks because (a) salt enters its cells (b) water comes out of its cells to establish an equilibrium (c) the cytoplasm of its cells begins to decompose (d) salt comes out of its cells 46. At the end of the experiment for determining the percentage of water absorbed by raisins, the raisins are wiped just before weighing. This is to ensure that (a) our hands do not get wet (b) the raisins lose water before weighing (c) only water absorbed by the raisins is weighed (d) the weighing scale does not get wet 47. 5 g raisins are soaked in 25 mL of ice-chilled water and 25 mL of tap water separately at room temperature. What will be the result after one hour? (a) The raisins in ice-chilled water will absorb more water than the raisins in tap water. (b) The raisins in tap water will absorb more water than the raisins in ice-chilled water. (c) The amounts of water absorbed by the raisins in both the conditions will be equal. (d) No water will be absorbed by the raisins in either condition. 48. The following photograph shows the process of

(a) endosmosis (c) plasmolysis 49. Spirogyra is an example of (a) blue-green algae (c) red algae

(b) exosmosis (d) absorption (b) brown algae (d) green algae

(a) Agaricus (c) Moss

(b) Spirogyra (d) Fern

54. Agaricus is commonly called (a) bread mould (b) black mould (c) mushroom (d) bracket fungi 55. Which of the following commonly grows on decaying organic matter during the rainy season? (a) Chlamydomonas (b) Mould (c) Spirogyra (d) Agaricus 56. Which of the following is a feature of Agaricus? (a) An umbrella-shaped, white, fleshy structure (b) A mycelial plant body (c) Saprophytic habit (d) All of these 57. In mushrooms, sexual reproduction occurs by the formation of spores on club-shaped structures called (a) mycelia (b) basidia (c) hyphae (d) sporangia 58. Which of the following is the group of simplest land plants? (a) Algae (b) Fungi (c) Bryophytes (d) Pteridophytes

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59. True roots and leaves are absent in (a) mosses (b) ferns (c) Pinus (d) angiosperms

71. What do earthworms eat? (a) Soil with organic matter (b) Leaves (c) Insects (d) Bacteria

60. Which of the following grow close together forming a velvety, matlike cover over the substratum? (a) Ferns (b) Mosses (c) Lichens (d) Fungi

72. Which characteristic feature of an earthworm makes it different from leeches? (a) The mode of locomotion (b) The mode of feeding (c) Musculature of its body (d) All of the above

61. The most developed seedless plants are (a) mosses (b) ferns (c) gymnosperms (d) angiosperms 62. Which of the following characters are found in ferns? (a) The plant body is differentiated into an aerial shoot system and an underground root system. (b) The leaves are divided into leaflets. (c) The plants have vascular tissues. (d) All of the above 63. Plants that have seeds, but lack flowers and fruits are (a) pteridophytes (b) ferns (c) gymnosperms (d) mosses 64. Which of the following is a conifer? (a) Cycas (b) Pea (c) Pinus (d) Mango 65. What are the differences between the male and female cones of Pinus? (a) The male cones are fewer than the female cones. (b) The male cones are larger than the female cones. (c) The male cones are smaller and many more than the female cones. (d) None of these 66. The seeds remain enclosed in a fruit in (a) mosses (b) ferns (c) gymnosperms (d) angiosperms 67. A rice plant is an example of a (a) dicot (b) monocot (c) gymnosperm

(d) fern

68. The leaves of a monocot plant have (a) reticulate venation (b) swelling at the base (c) parallel venation (d) all of these

73. An earthworm lacks (a) haemoglobin (c) nephridia

(b) teeth (d) pharynx

74. Leeches do not have (a) testes (c) gut

(b) distinct clitellum (d) suckers

75. The body of an earthworm is (a) thin and moist (b) hard and dry (c) yellow (d) black 76. Earthworms lack (a) nerves (c) kidney

(b) heart (d) haemoglobin

77. The largest cell of the body of an earthworm is in its (a) testis (b) ovary (c) intestine (d) coelomic fluid 78. Which structure in an earthworm is responsible for absorption? (a) Typhlosole (b) Gizzard (c) Hepatic caeca (d) Pharynx 79. Which of the following is a true worm? (a) Flatworm (b) Glow worm (c) Lugworm (d) Roundworm 80. Cockroaches are closely related to (a) crickets (b) mosquitoes (c) beetles (d) houseflies 81. Cockroaches live in (a) bright light (c) dry places

(b) dark places (d) ponds

82. The protective layer of the body of a cockroach is made up of (a) keratin (b) tannin (c) chitin (d) cartilage

69. The floral parts are usually pentamerous (5 in number) in (a) dicots (b) monocots (c) gymnosperms (d) all of these

83. The female and male cockroaches are (a) equal in size (b) winged (c) wingless (d) omnivorous

70. Where do earthworms live? (a) In cowdung (b) In the soil (c) In the intestine of birds (d) In human excreta

84. Cockroaches are (a) omnivorous (c) carnivorous

(b) insectivorous (d) sanguinivorous

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99. All fish are (a) scaly (c) devoid of medulla

85. A female cockroach lays eggs in a (a) nest (b) mesh (c) cocoon (d) water bag

(b) scaleless (d) active balancers

86. Which is the mode of feeding of cockroaches? (a) Sucking blood (b) Sucking milk (c) Biting and chewing (d) Lapping liquid food

100. The heart of a fish is (a) ventral (c) nonmuscular

(b) three-chambered (d) nonpulsatile

87. Cockroaches are known to be (a) cursorial (b) active fliers (c) sedentary (d) creepy insect

101. The scales of fish are (a) respiratory (c) excretory

(b) protective (d) glandular

88. The male and female distinguished by their (a) antennae (c) anal cerci

cockroaches

can

be

(b) eyes (d) anal styli

89. The pores through which air enters the body of a cockroach are called (a) spiracles (b) ostia (c) anus (d) cloaca 90. During copulation, cockroaches (a) take to flight (b) fight (c) come in head to tail contact (d) come in tail to tail contact 91. A baby cockroach is called (a) caterpillar (b) nymph (c) wriggler (d) tumbler 92. The upper lip of cockroach is called (a) maxilla (b) stipes (c) mandible (d) ligula 93. The total number of segments comprising head and thorax in cockroach is (a) 6 (b) 3 (c) 9 (d) 8 94. The most distant part of the leg of a cockroach is (a) coxa (b) tibia (c) trochanter (d) tarsus 95. The heart of a cockroach is (a) ventrally placed (b) tubular (c) laterally placed (d) four-chambered 96. Which of the following is correct? (a) All fish have a bony endoskeleton. (b) Some fish have a cartilaginous endoskeleton. (c) Gills in all fish are covered by an operculum. (d) All fish have gills as well as lungs.

102. The organ which regulates the buoyancy of fish in water is called (a) air sac (b) trachea (c) swim bladder (d) barb 103. Fish lack (a) liver (c) limbs

(b) endocrine gland (d) mucous gland

104. Birds lack (a) scales (c) wings

(b) urinary bladder (d) air sacs

105. Birds have beaks for (a) building nests (c) catching food

(b) fighting (d) all of these

106. Which of the following statements is correct? (a) All birds have special vocal sacs called syrinx. (b) All birds sing equally well. (c) All birds display courtship equally well. (d) All birds have solid, heavy bones. 107. Which of the following statements is correct? (a) All birds can see well at night. (b) A swan has to constantly move its legs to float in water. (c) Birds lay eggs in water. (d) Some birds are cold-blooded. 108. Which of the following statements is correct? (a) A sparrow is smaller than a pigeon. (b) Crows and ravens belong to the same species. (c) A kingfisher is larger than an ostrich. (d) The beak of a parrot is stronger than that of a kite. 109. Flightless birds are (a) very light (b) very heavy (c) lighter than game birds (d) totally wingless 110. The greatest variety of birds occurs in (a) Australia (b) South America (c) India (d) North America

97. Which of the following statements is correct? (a) All fish are jawless. (b) All fish are toothless. (c) Some fish have additional breathing organs. (d) Fish have haemoglobin in its RBC.

111. Which of these organs of a bird is not found in human? (a) Pecten (b) Intestine (c) Liver (d) Kidney

98. All fish lack (a) eyes (c) sexual organs

112. Which of the following is the largest bird? (a) Penguin (b) Ostrich (c) Peacock (d) Crane

(b) swim bladders (d) limbs

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113. Which gland in a bird helps it arrange feathers? (a) Green gland (b) Preen gland (c) Tear gland (d) Liver 114. Keel in the breastbone of a bird serves to (a) grasp food (b) digest food (c) attach flight muscles (d) perch on the branch 115. In which part of the body of a bird would you find pecten? (a) Eye (b) Nose (c) Leg (d) Ear 116. Which of the following protozoans cannot move about?

(a) I

(b) II

(c) III

(d) IV

120. Where is the respiratory organ located in the fish shown below? (IV) Dorsal fin Eye (I)

I

II

(a) I

III

(b) II

(c) III

IV

(d) IV

117. Which of the following animals possesses a water vascular system?

Anal fin (III)

(a) I

Operculum (II)

(b) II

(c) III

(d) IV

121. Which of the following holds true for root? (a) Positively phototropic (b) Negatively geotropic (c) Positively geotropic and negatively phototropic (d) Positively geotropic and positively phototropic 122. Root differs from stem due to (a) presence of hairs (b) absence of nodes (c) presence of buds (d) thickness (a) I

(b) II

(c) III

(d) IV

118. Where is the male genital aperture in the earthworm shown below? IV

I

Setae

II

Clitellum

(a) I

Genital papillae

(b) II

124. Region of cell division in roots is located just below (a) root cap (b) region of elongation (c) region of maturation (d) root hairs 125. Fibrous root is a type of (a) tap root (c) secondary root

Annuli

III

123. Absorption of water and minerals is the function of (a) root (b) stem (c) leaf (d) flower

(c) III

(d) IV

119. Which of the following part is absent in a female cockroach?

(b) Adventitious root (d) tertiary root

126. The major function of stem is (a) absorption of water (b) conduction of water (c) to hold branches and leaves (d) photosynthesis 127. Parallel venation is the characteristics of (a) dicot leaves (b) monocot leaves

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(c) both dicot and monocot leaves (d) none of these

(b) divided into ten parts (c) provided with compound eyes, wings and legs (d) provided with four equal-sized wings

128. All the floral parts are arranged on (a) petiole (b) thalamus (c) stamen (d) petals 129. Calyx and corolla are known as (a) essential whorls (b) accessory whorls (c) secondary whorls (d) reproductive whorls 130. Flower is a modified (a) vegetative bud (c) shoot

(b) leaf (d) axis

131. Which of the following constitute reproductive part of a flower? (a) Calyx (b) Corolla (c) Androecium (d) Gynoecium

male

132. The basal swollen portion of the pistil is called (a) filament (b) ovary (c) stigma (d) anther 133. The presence of characteristics of (a) dicots (c) bisexual plants

trimerous

flowers

is

the

(b) monocots (d) unisexual plants

134. Which one of the following is true for dicot plants? (a) Parallel venation (b) Trimerous flowers (c) Pentamerous flowers and reticulate venation (d) None of the above 135. The body of an adult mosquito is (a) divided into two parts

136. Eggs of mosquitoes are (a) red (b) rounded (c) shelled (d) oval- or cigar-shaped 137. Which is correct? (a) Eggs of all types of mosquitoes are of the same shape. (b) Larvae of all types of mosquitoes reproduce in water. (c) Larvae of mosquitoes never cast off skin. (d) Larvae are voracious eaters. 138. The larva of mosquito (a) breathes air (b) respires by gills (c) wriggles in water (d) has all the above characteristics 139. The pupa of mosquito is called (a) tumbler (b) grub (c) maggot (d) tadpole 140. Which is incorrect with respect to mosquitoes? (a) Different stages of development in mosquito are distinguishable. (b) Adult mosquitoes feed on algae. (c) Mosquitoes spread diseases such as malaria and dengue. (d) Mosquitoes have respiratory trumpets.

FOR CLASS 10 Multiple-Choice Questions Pick the correct option. 1. Small openings found widely scattered on the epidermis of leaves are called (a) lenticels (b) intercellular spaces (c) stomata (d) none of these 2. In dicot leaves, stomata are generally more on the (a) upper surface (b) lower surface (c) petiole (d) veins 3. In monocot leaves, stomata are present on the (a) lower surface (b) upper surface (c) lower and upper surfaces (d) petiole 4. The stomatal aperture remains surrounded by (a) cuticle (b) epidermal cells (c) guard cells (d) lenticels 5. Stomata remain open when guard cells are (a) flaccid (b) turgid (c) bean-shaped (d) dumb-bell-shaped

6. The maximum loss of water in transpiration is from (a) lenticels (b) cuticle (c) stomata (d) hydathodes 7. Stomata remain open during the day because the guard cells (a) help in exchange of gases (b) have thin walls (c) photosynthesize and produce sugars (d) are bean-shaped 8. Which of the following are function of the stomata? (a) Absorption (b) Translocation (c) Exchange of gases and transpiration (d) All of these 9. Presence of more stomata on the lower surface of a dicot leaf helps in (a) enhancement of transpiration (b) reduction of transpiration (c) unequal transpiration from the two surfaces (d) enhancement of photosynthesis 10. Dumb-bell-shaped guard cells are found in (a) gymnosperms (b) dicots (c) monocots (d) xerophytes

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11. Stomatal openings are under the control of (a) epidermal cells (b) palisade cells (c) spongy parenchyma cells (d) guard cells 12. Which side of the wall of a guard cell is thicker? (a) Lateral (b) Inner (c) Outer (d) All of these 13. In the following diagram of the lower surface of a leaf, what should be labelled as stoma?

139

21. The rate of photosynthesis is independent of (a) quality of light (b) duration of light (c) intensity of light (d) none of these 22. The oxygen liberated during photosynthesis is from (a) carbon dioxide (b) sugar (c) water (d) chlorophyll 23. Leaves are green because they (a) absorb blue and red light (b) absorb green light (c) do not absorb, but reflect green light (d) absorb and reflect green light 24. A balance between CO2 and O2 levels in plants is maintained by (a) transpiration (b) translocation (c) photosynthesis (d) nutrition

(a) I

(b) II

(c) III

(d) IV

14. At which wavelength (colour) of light does the maximum photosynthesis occur in plants? (a) Red (b) Green (c) White (d) Ultraviolet 15. At which wavelength of light does the least photosynthesis occur in plants? (a) Violet (b) Blue (c) Green (d) Red 16. The rate of photosynthesis is the highest when a plant is exposed to (a) continuous high light intensity (b) continuous low light intensity (c) alternating high and low light intensities (d) intermittent light 17. The light energy absorbed in photosynthesis helps to (a) activate chlorophyll (b) split water (c) reduce carbon dioxide (d) synthesize glucose 18. The rate of photosynthesis depends upon the (a) quality of light (b) quantity of light (c) quality and quantity of light (d) none of these 19. If a portion of a green leaf of a potted plant is covered with a black paper strip and the potted plant is exposed to sunlight for a few hours, what will happen in the covered portion? (a) Respiration will stop. (b) Respiration will be enhanced. (c) Starch will not be synthesized. (d) Starch will be synthesized. 20. The rate of photosynthesis is reduced considerably in green light because (a) green light does not activate chlorophyll molecules (b) chlorophyll molecules absorb only blue and red light (c) green light is reflected by the chlorophyll molecules (d) none of the above happens

25. The favoured respiratory substrate is (a) glucose (b) sucrose (c) maltose (d) glycogen 26. Carbon dioxide is released as a product during (a) photosynthesis (b) respiration (c) transpiration (d) ascent of sap 27. Respiration is (a) an anabolic process (c) a catabolic process

(b) a cyclic pathway (d) an aerobic process

28. Anaerobic and aerobic respiration release (a) ethyl alcohol (b) water (c) energy (d) lactic acid 29. For the complete oxidation of glucose to carbon dioxide and water organisms undergo (a) aerobic respiration (b) anaerobic respiration (c) fermentation (d) all of these 30. Germinating seeds help study respiration as they (a) photosynthesize rapidly (b) absorb CO2 (c) respire actively (d) release O2

the

rate

of

31. The experimental set-up shown below to demonstrate that CO2 is released during respiration will not yield the expected result because

(a) germinating seeds are not immersed in water (b) the delivery tube is dipped in water

Foundation Sci Bio Class 10 140

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Foundation Science: Biology for Class 10

42. Which of the following best represents multiple fission?

(c) the flask is not airtight (d) there is no KOH solution in the flask 32. Binary fission is the mode of reproduction in (a) algae (b) fungi (c) Amoeba (d) yeast

I

33. The division of one cell into two new similar daughter cells is called (a) binary fission (b) multiple fission (c) sporulation (d) budding

(a) I

48. The uppermost cell of suspensor swells and forms (a) globular embryo (b) heart-shaped embryo (c) vesicular cell (d) radicle 49. Hypophysis forms part of (a) stem (b) radicle and root cap (c) embryo (d) vesicle

(b) internal (d) none of these

50. The mature dicot embryo appears (a) heart-shaped (b) globular (c) straight (d) none of these

40. Which of the following is the correct diagram showing binary fission in Amoeba?

III

51. What is the basis of having homologous organs? (a) Organisms living in the same habitat have homologous organs. (b) Organisms living in different habitat have homologous organs. (c) Organisms lead a sedentary life. (d) Organisms are very agile.

IV

(c) III

(d) IV

41. What does the figure given below show? Nucleus Daughter nuclei

(b) female gamete (d) vegetative cell

47. The length of the suspensor is (a) one-celled (b) two-celled (c) three-celled (d) six to ten-celled

38. Yeasts are examples of unicellular (a) algae (b) fungi (c) bacteria (d) prokaryotes

(b) II

(d) IV

46. The lowest cell of suspensor is called (a) vesicle (b) radicle (c) hypophysis (d) root cap

37. The formation of bulblike outgrowths that become detatched from the body of the parent is called (a) binary fission (b) budding (c) sporulation (d) grafting

(a) I

(c) III

IV

45. Suspensor is formed by transverse divisions of (a) terminal cell (b) basal cell (c) hypophysis (d) vesicle

36. Binary fission takes place in (a) unfavourable conditions (b) favourable conditions (c) hot conditions (d) all conditions

II

III

44. The first division of zygote is (a) transverse (b) vertical (c) longitudinal (d) none of the above

35. In binary fission, the genome divides (a) amitotically (b) mitotically (c) meiotically (d) none of these

I

(b) II

43. Embryo is formed from (a) male gamete (c) zygote

34. Which of the following is the simplest method of asexual reproduction? (a) Budding (b) Sporulation (c) Binary fission (d) Multiple fission

39. The buds of yeasts are (a) external (c) external and internal

II

52. Study of homologous organs suggests that (a) evolution has stopped (b) evolution is very rapid (c) there is some kind of attempt to exploit different habitats (d) evolution has not taken any advantage of the habitats

Bud

Vacuole

(a) Amoeba undergiong binary fission. (b) Yeast undergoing budding. (c) Amoeba undergoing budding. (d) Yeast undergoing binary fission.

F

53. Comparative anatomy elucidates (a) the path of evolution (b) speed of evolution (c) pattern of evolution (d) both (a) and (c)

Foundation Sci Bio Class 10 141

Practicals

141

• ANSWERS • FOR CLASS 9 1. (c)

2. (d)

3. (a)

4. (c)

5. (b)

6. (d)

7. (a)

8. (b)

9. (a)

10. (c)

11. (d)

12. (b)

13. (d)

14. (a)

15. (c)

16. (c)

17. (d)

18. (c)

19. (b)

20. (a)

21. (d)

22. (c)

23. (c)

24. (b)

25. (c)

26. (b)

27. (c)

28. (a)

29. (c)

30. (d)

31. (d)

32. (b)

33. (a)

34. (d)

35. (b)

36. (a)

37. (d)

38. (b)

39. (c)

40. (b)

41. (b)

42. (c)

43. (b)

44. (c)

45. (b)

46. (c)

47. (b)

48. (a)

49. (d)

50. (b)

51. (d)

52. (b)

53. (b)

54. (c)

55. (d)

56. (d)

57. (b)

58. (c)

59. (a)

60. (b)

61. (b)

62. (d)

63. (c)

64. (c)

65. (c)

66. (d)

67. (b)

68. (c)

69. (a)

70. (b)

71. (a)

72. (d)

73. (b)

74. (b)

75. (a)

76. (c)

77. (b)

78. (a)

79. (d)

80. (a)

81. (b)

82. (c)

83. (d)

84. (a)

85. (c)

86. (c)

87. (a)

88. (d)

89. (a)

90. (d)

91. (b)

92. (c)

93. (c)

94. (d)

95. (b)

96. (b)

97. (c)

98. (d)

99. (d)

100. (a)

101. (b)

102. (c)

103. (c)

104. (b)

105. (d)

106. (a)

107. (b)

108. (a)

109. (b)

110. (b)

111. (a)

112. (b)

113. (b)

114. (c)

115. (a)

116. (d)

117. (a)

118. (c)

119. (d)

120. (b)

121. (c)

122. (b)

123. (a)

124. (a)

125. (b)

126. (c)

127. (b)

128. (b)

129. (b)

130. (c)

131. (c)

132. (b)

133. (b)

134. (c)

135. (c)

136. (d)

137. (d)

138. (d)

139. (a)

140. (b)

FOR CLASS 10 1. (c)

2. (b)

3. (c )

4. (c)

5. (b)

6. (c)

7. (c)

8. (c)

9. (b)

10. (c)

11. (d)

12. (b)

13. (c)

14. (a)

15. (c)

16. (d)

17. (a)

18. (c)

19. (c)

20. (c)

21. (d)

22. (c)

23. (c)

24. (c)

25. (a)

26. (b)

27. (c)

28. (b)

29. (a)

30. (c)

31. (d)

32. (c)

33. (a)

34. (c)

35. (a)

36. (b)

37. (b)

38. (b)

39. (a)

40. (d)

41. (b)

42. (d)

43. (c)

44. (a)

45. (b)

46. (c)

47. (d)

48. (c)

49. (b)

50. (a)

51. (b)

52. (c)

53. (d)

v

Foundation Sci Bio Class 10 142

Question Bank 1. Nutrition (viii) Projections of cytoplasm surrounding food in Amoeba

A. Very-Short-Answer Questions 1. Name the organelle where photosynthesis takes place. 2. What role is photosynthesis?

played

by

stomata

5. What will be the result if two green plants are kept separately, one in continuous light and the other in dark, oxygen-free condition?

during

3. From where does a plant obtain water for photosynthesis?

6. How does an autotroph differ from a heterotroph?

4. What is similar among animals, fungi and some bacteria?

7. Write the sequence of important events taking place during photosynthesis.

5. In which form is food stored in plants and in animals?

8. What would be the consequence if all green plants are eliminated from earth?

6. Why are chlorophyll molecules essential for photosynthesis?

9. If CO2 is not released by the plants during day time, what inference would you draw and why?

7. Give two examples of heterotrophs. 8. Why are heterotrophs called consumers?

10. Do you agree with this statement that all plants release oxygen during day and CO2 during night? Explain.

9. What are saprophytes? 10. Give two examples of saprophytes.

11. How does the movement of food take place inside the alimentary canal?

11. Name the watery substance released in our mouth during eating.

12. Name the substrates on which enzymes lipase, amylase, pepsin and trypsin act.

12. What does saliva contain? 13. Where does peristaltic movement occur?

13. Mention the roles played by gastric glands found in the wall of stomach.

14. Name the structures through which food reaches the stomach from our mouth.

14. Why does small intestine play an important role in the absorption of digested food?

15. Which is the longest part of the alimentary canal? 16. From where is bile secreted?

15. What is the role of mouth in digestion of food?

17. Where is bile stored? 18. Which type of organ is vermiform appendix?

16. What is alimentary canal in human beings?

19. Where are villi located?

17. What is mucus? What will be the result if it is not secreted by the gastric glands?

B. Short-Answer Questions 1. Why is nutrition essential for an organism?

18. The small intestine in herbivores is longer than that in carnivores. Why?

2. In which respect are leeches, ticks and Cuscuta similar?

19. What is the importance of emulsification of fats? 20. What role does salivary amylase play?

3. What will be the effect of the following conditions on the rate of photosynthesis? (i) Dry conditions (ii) Closed stomata (iii) Rainy days (iv) Sunny days (v) Good manuring 4. Give proper terms for the following. (i) Site of photosynthesis (ii) Organisms dependent on other organisms for their food (iii) The process which converts solar energy into chemical energy (iv) Organisms capable of synthesizing food (v) Cells surrounding stoma (vi) The muscular movement taking place in oesophagus (vii) An enzyme that breaks down protein in stomach

21. What is the function of pancreas? 22. What happens to the undigested food? C. Long-Answer Questions 1. Describe different photosynthesis.

factors

which

affect

2. Describe the mechanism of digestion of fats, proteins and carbohydrates in human beings. 3. Discuss the role of different glands in human digestive system. 4. Describe different types of heterotrophic nutrition. How do they differ from each other and from autotrophic nutrition? 5. How can you prove the essentiality of CO2 and sunlight for photosynthesis? 142

Foundation Sci Bio Class 10 143

Question Bank

(c) 6CO2 + 12H2 O ® C 6 H12 O6 + 6O2 + 6H2 O

D. Crossword Puzzle

(d) 6CO2 + 6H2 O ® C 6 H12 O6 + 6CO2 + 6H2 O

1 3 2 7 4

5

6 8

Down 1. 3. 5. 7.

Organelle for photosynthesis Mechanism for food production in green plants Chemical nature of bile Bile and pancreatic ducts open here

Across 2. 4. 6. 8.

143

Organism making its own food Muscular and tubular part of alimentary canal A parasitic plant Middle part of small intestine

E. Diagrammatic Questions 1. Draw a cross section of a leaf and locate the regions of chloroplast, stomata and air spaces. 2. With the help of diagrams show how food is engulfed by Amoeba. 3. Label the following parts after drawing the diagram of human alimentary canal: mouth, oesophagus, liver, stomach, small intestine, appendix. 4. Draw a diagram to show the network of blood capillaries in the villi of small intestine. F. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. Which of the following enzymes get mixed with food in our mouth? (a) Trypsin (b) Cellulose (c) Pepsin (d) Amylase 2. The mode of nutrition in mushrooms is (a) heterotrophic (b) autotrophic (c) holozoic (c) parasitic 3. The most appropriate equation for photosynthesis will be (a) 6CO2 + 6H2 O+ Sunlight ® C 6 H12 O6 + O2 + 6H2 O (b) 6CO2 + 12H2 O+ Sunlight + Chlorophyll ® C 6 H12 O6 + 6O2 + 6H2 O

4. Which of the following statements are true about autotrophs? (a) They convert carbon dioxide and water into carbohydrates in presence of light. (b) They store carbohydrates in the form of starch. (c) They occupy second trophic level in food chains. (d) They are chlorophyll-bearing organisms. 5. Which of the following events takes place during photosynthesis? (a) Trapping of light energy by chlorophyll molecules (b) Conversion of light energy to chemical energy (c) Reduction of CO 2 to carbohydrates (d) Release of CO 2 in the atmosphere 6. In which of the following groups of organisms food material is broken down outside the body? (a) Cuscuta, Amoeba, green plants (b) Amoeba, Paramoecium, Cuscuta (c) Yeast, green plants, mushroom (d) Mushroom, bread mould, yeast 7. In human body, food is finally digested in (a) large intestine (b) small intestine (c) stomach (d) oesophagus 8. Which of the following protects the inner lining of stomach from hydrochloric acid? (a) Mucus (b) Bile (c) Pepsin (d) Amylase 9. Select the incorrect statement(s). (a) Heterotrophs contain chlorophyll pigments. (b) Heterotrophs can convert solar energy to chemical energy. (c) Heterotrophs are unable to synthesize food. (d) Heterotrophs occupy first trophic level in food chain. 10. During photosynthesis oxygen is evolved from (a) CO 2 (b) water (c) glucose (d) chlorophyll 11. The food in autotrophs is reserved in the form of (a) protein (b) fatty acid (c) glycogen (d) starch 12. Which of the following is the correct sequence representing human alimentary canal? (a) Mouth ® oesophagus ® stomach ® small intestine ® large intestine (b) Mouth ® small intestine ® stomach ® oesophagus ® large intestine (c) Mouth ® stomach ® oesophagus ® small intestine ® large intestine (d) Mouth ® stomach ® oesophagus ® large intestine ® small intestine

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Foundation Science: Biology for Class 10

13. The muscular and tubular part of the alimentary canal is called (a) pharynx (b) small intestine (c) oesophagus

(d) stomach

14. Which of the following functions is carried out by pancreatic juice? (a) Lipase emulsifies fats and trypsin digests proteins. (b) Lipase digests carbohydrates and trypsin digests fats. (c) Lipase emulsifies both carbohydrates and fats. (d) Trypsin digests both proteins and fats. 15. Pancreatic juice is carried by the pancreatic duct into (a) large intestine (b) liver (c) duodenum (d) stomach 16. Bile is produced by (a) pancreas (c) small intestine

(b) liver (d) stomach

17. Iodine solution is used to test the presence of (a) proteins (b) fats (c) starch

(d) enzymes

18. Which part of alimentary canal receives bile? (a) Oesophagus (b) Pharynx (c) Large intestine (d) Small intestine 19. Absence of salivary amylase in the saliva will not affect (a) breakdown of protein in mouth

25. The inner lining of the small intestine has numerous finger-like projections called (a) jejunum (b) duodenum (c) ileum (d) villi 26. The undigested food is finally removed from the body through (a) large intestine (b) small intestine (c) anus (d) villi II. Fill in the blanks. 1. Nutrition provides ...... to the body. 2. Since autotrophic plants are able to produce food, they are also called ...... . 3. ...... are the main sites of photosynthesis. 4. Chlorophyll is mainly found in the ...... . 5. The opening and closing of stomata is regulated by ...... . 6. ...... energy is used in splitting water molecules into hydrogen and oxygen. 7. During photosynthesis light energy is converted into ...... . 8. Heterotrophic organisms obtain food from ...... organisms. 9. Amoeba exhibits ...... nutrition.

(b) breakdown of fat in mouth

10. The oral cavity opens into the ...... .

(c) breakdown of starch in mouth

11. ...... pairs of salivary glands are present in human mouth.

(d) assimilation of vitamins in mouth 20. The process of photosynthesis requires (a) chlorophylls and light only (b) chlorophylls and CO 2 only (c) chlorophylls, CO 2 and H 2 O only (d) chlorophylls, CO 2 , H 2 O and light 21. Nitrogen, an essential element used in the synthesis of proteins, is obtained by plants in the form of (a) atmospheric nitrogen (b) nitrates and nitrites (c) amino acids (d) peptides 22. Water used in photosynthesis by terrestrial plants is taken up from (a) air (b) soil (c) either from air or from soil (d) none of the above 23. The mode of nutrition in parasitic organisms is (a) heterotrophic (b) autotrophic (c) both autotrophic and heterotrophic (d) none of the above 24. Which of the following parts is the site of the complete digestion of carbohydrates, proteins and fats? (a) Oesophagus (b) Stomach (c) Small intestine

(d) Large intestine

12. ...... is the muscular and tubular part of the alimentary canal. 13. ...... is the muscular partition between the chest cavity and the abdominal cavity. 14. ...... serves as a storehouse of food where partial digestion takes place. 15. ...... is the first part of small intestine. 16. Bile is yellowish ...... juice. 17. Pancreatic juice contains ...... for the breakdown of fat. 18. Herbivores have longer small intestine to digest ...... . 19. The digested food is taken up by the walls of the ...... . 20. The undigested material is removed from the body via ...... . III. Write Yes/No. 1. Is the general requirement for energy and material common in all organisms? 2. Are carbohydrates stored in the form of starch in plants? 3. Is it true that light energy is not directly absorbed by chlorophyll molecules?

Foundation Sci Bio Class 10 145

Question Bank

4. Are guard cells devoid of chloroplast?

145

V. Match the columns.

5. Are autotrophs dependent upon heterotrophs for their food requirements?

1.

A

B

(i) Chlorophyll (ii) Heterotrophic nutrition (iii) Leaves

6. Is nitrogen an essential element in the synthesis of proteins? 7. Is Cuscuta a parasitic plant? 8. Does food mix thoroughly with saliva in our mouth when we chew properly? 9. Does gall bladder store pepsin?

(a) Autotroph (b) Parasite (c) Food reserve in plants (d) Consumers (e) Saprophyte (f) Digestion in food vacuoles (g) Photosynthesis (h) Stomata

(iv) Cuscuta (v) Starch (vi) Green plants

10. Is large intestine the site of complete digestion of proteins? IV. Mark the statements true (T) or false (F).

(vii) Mushroom (viii) Paramoecium

1. Carbon and energy requirements of the autotrophic organisms are fulfilled by photosynthesis. 2.

2. Oxygen is released during photosynthesis.

A

B

3. CO2 is not essential for photosynthesis.

(i) Leech

(a) Bile

4. The alimentary canal and the glands associated with digestion constitute the human digestive system.

(ii) Amoeba

(b) Pepsin

5. Stomach serves as a storehouse of food where complete digestion takes place.

(iii) Liver

(c) Pancreatic juice

(iv) Salivary amylase

(d) Undigested food

(v) Gastric glands

(e) Inner lining of small intestine

(vi) Trypsin

(f) Parasitic nutrition

(vii) Large intestine

(g) Extensive coiling

(viii) Villi

(h) Pseudopodia

6. Bile produced by liver is acidic in nature. 7. Ileum is the last and main part of the small intestine. 8. Gastric glands are present in small intestine. 9. Carnivores like tigers have a shorter small intestine because meat is easier to digest 10. Small intestine receives the secretions of liver and pancreas.

(ix) Small intestine

(i) Peptic ulcer

(x) Stomach

(j) Mouth

F • ANSWERS • 6. (d) 7. (b) 8. (a) 9. (a), (b), (d) 10. (b)

A. 1. Chloroplast 2. CO2 enters the leaves and O2 is released into air through stomata. 3. Water is absorbed from soil. 4.They cannot prepare their own food. 5. Starch in plants and glycogen in animals 6. Chlorophyll absorbs light energy from sunlight. 7. Mushrooms and human beings 8. They obtain food from other sources. 9. They obtain food from dead organisms. 10. Bread moulds, yeasts 11. Saliva 12. Mucin and salivary amylase 13. Oesophagus 14. Pharynx and oesophagus 15. Small intestine 16. Liver 17. Gall bladder 18. Vestigial 19. On the wall of the ileum in the small intestine D. Down: 1. Chloroplast 3. Photosynthesis 5. Alkaline 7. Duodenum Across: 2. Autotroph 4. Oesophagus 6. Cuscuta 8. Jejunum F.

I.

1. (d) 2. (a) 3. (b) 4. (a), (b), (d)

11. (d) 12. (a) 13. (c) 14. (a) 15. (c) 16. (b) 17. (c) 18. (d) 19. (a), (b), (d) 20. (d) 21. (b) 22. (b) 23. (a) 24. (c) 25. (d) II.

III.

26. (c)

1. nutrients 2. producers 3. Chloroplasts 4. leaves 5. guard cells 6. Light 7. chemical energy 8. other 9. holozoic 10. pharynx 11. Three 12. Oesophagus 13. Diaphragm 14. Stomach 15. Duodenum 16. alkaline 17. lipase 18. cellulose 19. intestine 20. anus 1. Yes 2. Yes 3. No

4. No 5. No 6. Yes

7. Yes 8. Yes 9. No 10. No IV.

1. T 2. T 3. F 4. T 5. F 6. F 7. T 8. F 9. T 10. T

V.

5. (a), (b), (c)

v

1. (i)(g) (ii)(d) (iii)(h) (iv)(b) (v)(c) (vi)(a) (vii)(e) (viii)(f) 2. (i)(f) (ii)(h) (iii)(a) (iv)(j) (v)(b) (vi)(c) (vii)(d) (viii)(e) (ix)(g) (x)(i)

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Foundation Science: Biology for Class 10

2. Respiration A. Very-Short-Answer Questions

D. Crossword Puzzle

1. By which respiratory process is lactic acid formed?

3

2. Name the process through which glucose is broken down to pyruvic acid. 3. Where does anaerobic respiration take place? 4. Name the organism which converts pyruvate to ethanol.

1 2

5. Where does the second stage of aerobic respiration take place? 4

6. Name the organs through which gaseous exchange takes place in plants. 7. Name the respiratory organs found in animals.

5

8. Do the hair present inside our nose play any role? 9. Where is pharynx located?

6

10. Name the structure which prevents food from entering the passage to the lungs. 11. Why are cartilage rings present inside trachea? 12. How are bronchi formed? 13. Name the structures formed by the division of bronchioles. 14. Name the respiratory pigments of human beings. B. Short-Answer Questions 1. What is the energy currency in the living organisms? How is it produced? 2. Why do animals need more energy as compared to plants? 3. Describe how the guard cells regulate the opening and closing of stomata? 4. What will happen if fish are taken out of water? Explain with reason. 5. What will be the consequence if the leaves of a healthy potted plant were coated with vaseline? Explain with reason. 6. What happens to pyruvate when oxygen is available? 7. Why do our leg muscles cramp when we run for a long period? 8. What will happen if we inhale carbon monoxide in place of oxygen? 9. With regard to energy production, which type of respiration is more efficient? Why is it so? 10. How does exchange of gases take place in small organisms? C. Long-Answer Questions 1. Describe the three pathways of glucose breakdown in living organisms. 2. What is breathing? How does it take place in man? 3. Discuss the exchange of gases in plants. 4. Describe the structure and functions of different organs involved in human respiratory system.

Down 1. Voice box in human beings 3. Anaerobic respiration by yeast 5. Respiratory organ of fish Across 2. 4. 5. 6.

Windpipe Product of glycolysis The opening leading to the voice box Common respiratory substrate

E. Diagrammatic Questions 1. Draw a flow chart to show different ways of oxidation of glucose. 2. Draw an experimental set-up to demonstrate that CO2 is evolved during fermentation. 3. Draw a diagram to show the structure and position of stomata on a leaf. 4. Draw a clean diagram of human respiratory system and label the following structures: Glottis, larynx, trachea, bronchus, bronchioles and diaphragm 5. Draw a diagram to show an alveolus and the surrounding blood capillaries. F. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. Which part of human cell is involved in conversion of pyruvic acid into lactic acid during deficiency of oxygen? (a) Golgi body (b) Mitochondria (c) Cytoplasm (d) Lysosome 2. Which of the following gases turns lime water milky when we blow air into it from mouth? (a) Oxygen (b) Carbon dioxide (c) Nitrogen (d) Carbon monoxide

Foundation Sci Bio Class 10 147

Question Bank

3. Which of the following processes is responsible for cramps in the muscles of sportsmen? (a) Nonconversion of glucose to pyruvate (b) Conversion of pyruvate to lactic acid due to deficiency of oxygen (c) Conversion of pyruvate to glucose in presence of oxygen (d) Conversion of pyruvate to ethanol 4. Which of the following equations represents anaerobic respiration in yeast? cytoplasm

(a) Glucose ¾ ¾ ¾ ¾® Pyruvate cytoplasm

¾ ¾ ¾ ¾® Ethanol + CO 2 cytoplasm

(b) Glucose ¾ ¾ ¾ ¾® Pyruvate mitochondria ¾ ¾ ¾ ¾ ¾® Lactic acid mitochondria (c) Glucose ¾ ¾ ¾ ¾ ¾® Pyruvate cytoplasm

¾ ¾ ¾ ¾® Ethanol + CO 2 mitochondria

(d) Glucose ¾ ¾ ¾ ¾ ¾® Lactic acid cytoplasm

¾ ¾ ¾ ¾® Ethanol + CO 2 5. Which of the following statement(s) is/are correct? (a) Fermentation is a form of aerobic respiration. (b) Aerobic respiration involves mitochondria. (c) Lactic acid is formed in human muscle cells during anaerobic respiration. (d) Pyruvate can be converted into ethanol in mitochondria. 6. Which of the following represents the correct sequence of air passage during inhalation? (a) Nostrils ® larynx ® pharynx ® alveoli ® lungs (b) Nostrils ® trachea ® pharynx ® larynx ® lungs (c) Nostrils ® pharynx ® larynx ® trachea ® alveoli (d) Nostrils ® alveoli ® pharynx ® larynx ® lungs 7. The opening and closing of stomatal pore is regulated by (a) O 2 concentration (b) CO 2 concentration (c) temperature (d) turgidity of guard cells 8. Choose the correct statement(s) amongst the following. (a) For regulating different life processes energy is required. (b) Living organisms grow with time. (c) Living organisms need to repair and maintain their structures. (d) Molecules within the cells do not exhibit movement. 9. During respiration exchange of O 2 and CO 2 takes place in (a) pharynx and larynx (b) trachea and lung (c) alveoli of lungs (d) larynx and throat

147

10. Which of the following statement(s) is/are not correct? (a) Bronchus is divided into bronchioles. (b) The opening leading to the larynx is called glottis. (c) During inhalation, ribs move inward and diaphragm is raised. (d) Oxygen has more affinity with haemoglobin than CO 2 . 11. Choose the correct statement(s). (a) Alveoli increase the surface area for exchange of gases. (b) Oxygen from alveolar air diffuses into blood and CO 2 from blood diffuses into alveolar air. (c) From the larynx the air goes to pharynx. (d) The trachea is not connected to bronchi. 12. Which of the following is the correct representation of aerobic respiration? cytoplasm

(a) Glucose ¾ ¾ ¾ ¾® Ethanol mitochondria ¾ ¾ ¾ ¾ ¾® CO 2 + H 2 O cytoplasm

(b) Glucose ¾ ¾ ¾ ¾® Pyruvate mitochondria ¾ ¾ ¾ ¾ ¾® CO 2 + H 2 O cytoplasm

(c) Glucose ¾ ¾ ¾ ¾® Pyruvate + Energy mitochondria ¾ ¾ ¾ ¾ ¾® CO 2 + H 2 O + Energy mitochondria

(d) Glucose ¾ ¾ ¾ ¾ ¾® Pyruvate cytoplasm

¾ ¾ ¾ ¾® CO 2 + H 2 O + Energy 13. Which of the following overall reactions is true representation of respiration? (a) C 6 H12 O6 + O2 ® 6CO2 + 6H2 O (b) 6C 6 H12 O6 + 6O2 ® 6CO2 + 6H2 O+ Energy (c) C6 H12 O6 + O2 ® 6CO2 + 12H2 O (d) C 6 H12 O6 + 6O2 ® 6CO2 + 6H2 O+ Energy 14. Pyruvate is not a (a) 6-carbon molecule (c) 4-carbon molecule

(b) 3-carbon molecule (d) 5-carbon molecule

15. The amount of energy released after aerobic respiration is (a) less than that after anaerobic respiration (b) much more than that after anaerobic respiration (c) almost equal to that after anaerobic respiration (d) about half of that after anaerobic respiration 16. Which of the following is not a 3-carbon molecule? (a) Pyruvate (b) Ethanol (c) Lactic acid (d) All of the above 17. As compared to terrestrial organisms, the rate of breathing in aquatic organisms is (a) slightly slower (b) much faster (c) almost the same (d) much slower 18. Which of the following respiratory structures has cartilage rings to prevent it from collapsing? (a) Nasal cavity (b) Pharynx (c) Larynx (d) Trachea

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19. Balloon-like structures present inside the lungs are called (a) alveoli (b) bronchioles (c) bronchi (d) alveolar ducts

III. Write Yes/No. 1. Do plants exchange gases through stomata? 2. Is pyruvate formed in mitochondria? 3. Does the breakdown of pyruvate using oxygen take place in mitochondria?

20. Haemoglobin, the respiratory pigment is not found in (a) WBC (b) RBC (c) platelets (d) plasma

4. Is it true that the organisms that live in water do not use the oxygen dissolved in water?

21. As compared to CO 2 , carbon monoxide binds to haemoglobin (a) loosely (b) very strongly (c) either loosely or strongly (d) without any force

5. Are the balloon-like structures present in our lungs called alveoli?

22. A pair of spongy organs lying in the chest cavity is called (a) hearts (b) kidneys (c) lungs (d) bronchioles

7. Is haemoglobin present in WBC?

6. Does our chest cavity become smaller when we breathe in? 8. Are lungs a pair of spongy organs lying in the chest cavity formed by the ribs? 9. Does the actual exchange of gases between air and the human body take place in the alveoli?

23. Which of the following structures increase the total surface area for the exchange of gases in the lungs? (a) Bronchi (b) Alveoli (c) Bronchioles (d) Trachea

10. Do different parts independently?

of

the

plant

respire

IV. Mark the statements true (T) or false (F).

II. Fill in the blanks.

1. Glycolysis takes place in the cytoplasm of the cell.

1. Pyruvate may be converted into ethanol and CO2 during ...... .

2. Anaerobic reactions after glycolysis produce lactic acid, or ethanol.

2. ATP is the ...... for most cellular processes.

3. As compared to aerobic respiration, anaerobic respiration produces more energy.

3. The walls of the alveoli contain an extensive network of ...... .

4. ATP is formed in the cytoplasm.

4. The complete process of anaerobic respiration takes place in ...... .

5. The build-up of ethanol in our muscles causes cramps.

5. Glucose is completely oxidized into CO2 , H2 O and energy during ...... .

6. The energy released during cellular respiration is not used immediately to synthesize ATP.

6. In plants, respiration occurs at a much ...... rate than in animals.

7. Rings of cartilage are present in the throat. 8. The lungs always contain residual volume of air.

7. Human lungs have ...... of air sacs for the exchange of gases.

9. Carbon monoxide binds haemoglobin than oxygen.

8. ...... are respiratory organs found in aquatic animals.

more

strongly

to

10. All alveoli are not covered by web of blood capillaries.

9. When air passes through the nose, it is warmed, moistened and ...... .

V. Match the columns.

10. The opening leading to the larynx is called ...... .

A

11. From the larynx air goes to ...... . 12. Each bronchus divides and branches out in the form of thinner tubes called ...... .

(i) (ii) (iii) (iv) (v) (vi) (vii) (viii)

13. The oxygen picked up by haemoglobin gets ...... with blood to various ...... . 14. The first step of aerobic respiration takes place in ......, while the second step takes place in the ...... . 15. Accumulation of excess ...... in the muscles causes pain. 16. Terrestrial animals use ...... of the atmosphere for respiration.

Glycolysis Human muscles Mitochondria Yeast Pyruvate Fish Larynx Trachea

(ix) Mammals (x) Alveoli

17. Reptiles, birds and ...... have lungs for the exchange of gases.

F

B

(a) (b) (c) (d) (e) (f) (g) (h)

Fermentation 3-carbon compound Gills Epiglottis Cytoplasm Lactic acid Lungs Balloon-like structures (i) Cartilage rings (j) ATP synthesis

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149

• ANSWERS • 7. (d) 8. (a), (b), (c) 9. (c) 10. (c), (d) 11. (a), (b) 12. (c) 13. (d) 14. (a), (c), (d) 15. (b) 16. (b) 17. (b) 18. (d) 19. (a) 20. (a), (c), (d) 21. (b) 22. (c) 23. (b), (c)

A. 1. Anaerobic respiration 2. Glycolysis 3. Cytoplasm 4. Yeast 5. Mitochondria 6. Stomata and intercellular spaces in the leaves, and lenticels 7. Lungs, trachea and gills 8. They filter the air entering our nose. 9. Pharynx is located just behind the nose. 10. Epiglottis 11. So that the walls of the trachea do not collapse 12. Trachea branches out to form bronchi. 13. Bronchioles divide to form alveolar duct. 14. Haemoglobin

II. 1. fermentation 2. energy currency 3. blood vessels 4. cytoplasm 5. aerobic respiration 6. slower 7. millions 8. Gills 9. filtered 10. glottis 11. trachea 12. bronchioles 13. transported, tissues 14. cytoplasm, mitochondria 15. lactic acid 16. oxygen 17. mammals III. 1. Yes 2. No 3. Yes 4. No 5. Yes 6. No 7. No 8. Yes 9. Yes 10. Yes IV. 1. T 2. T 3. F 4. F 5. F 6. F 7. T 8. T 9. T 10. F

D. Down: 1. Larynx 3. Fermentation 5. Gills Across: 2. Tracheae 4. Pyruvate 5. Glottis 6. Glucose F.

V. 1. (i)(e) (ii)(f) (iii)(j) (iv)(a) (v)(b) (vi)(c)

I. 1. (c) 2. (b) 3. (b) 4. (a) 5. (b), (c) 6. (c)

(vii)(d) (viii)(i) (ix)(g) (x)(h)

v

3. Transportation A. Very-Short-Answer Questions 1. Which chamber of the heart receives impure blood from the body? 2. Where does blood go from the right ventricle? 3. What is the function of heart valves? 4. What is the relation between heart and lungs? 5. Define single heart. 6. Define double heart. 7. Define transitional heart. B. Short-Answer Questions 1. Differentiate between artery and vein. 2. Differentiate between atrium and ventricle. 3. What is the difference between heart of fish and that of frog? 4. Write down the essential features of fish heart. 5. In what respect is double-circuit heart better than single-circuit heart? 6. Why is the wall of the ventricle thicker than that of the atrium? 7. Why is the force of blood greater in arteries than in veins? 8. What is the function of pacemaker? 9. What is the role of haemoglobin in transport? C. Long-Answer Questions 1. 2. 3. 4.

Explain the advantages of double heart. What is the significance of blood vascular system? What are the components of circulatory system? Describe the heart of a mammal and compare it with that of a fish. 5. What is the role of sinoatrial node?

6. Write an essay on the role of corpuscles in circulatory system. D. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. Which of the following is/are correct about heart? (a) Left ventricle receives pure blood. (b) Right ventricle pumps impure blood. (c) Left atrium has thicker wall than the right ventricle. (d) Right atrium opens into the left ventricle. 2. When heart contracts to pump blood, the flow has to be unidirectional. This is ensured by (a) valves (b) muscles (c) SA node (d) pericardium 3. Single circulation is shown in which group? (a) Sharks, whales (b) Flying fish, bats (c) Tree frogs, climbing perch (d) Gold fish, carps 4. Double circulation can be seen in (a) turtle (b) chimpanzee (c) boa (d) dog 5. Which is/are incorrect? (a) Right ventricle has the thickest wall. (b) Left ventricle has the thickest wall. (c) Valves are located in the left side. (d) Pacemaker lies in the right side of the heart. 6. What is correct about pulmonary artery? (a) It contains pure blood. (b) It contains impure blood.

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7.

8.

9.

10.

Foundation Science: Biology for Class 10

(c) It sends blood to the gills. (d) It sends blood to the walls of the heart. What is correct about pulmonary vein? (a) It supplies blood to the valves. (b) It is the longest vein. (c) It has pure blood that comes from the liver. (d) It brings pure blood to the left atrium. How is a vein different from an artery? (a) In carrying deoxygenated blood (b) In having greater elasticity (c) In having valves (d) All of the above Pacemaker of the heart is (a) nervous tissue (b) situated in the left atrium (c) muscular tissue (d) none of the above Heartbeat depends upon (a) size of the animal (b) physical activity (c) pacemaker (d) all of the above

2. Blood capillaries are lined with cuboidal cells. 3. Cardiac muscles are voluntary. 4. Pericardial fluid is called lymph. 5. In fish, the heart receives only pure blood. 6. The velocity of blood in veins is greater than that in arteries. 7. Lymph and plasma have the same chemical composition. IV. Match the columns. A

II. Fill in the blanks. 1. Heart is situated in the middle of the ...... cavity.

B

(i) Right atrium

(a) Oscilloscope screen

(ii) ECG

(b) Amphibia

(iii) Auricle

(c) Vena cava

(iv) Three-chambered heart

(d) Fish

(v) Two-chambered heart

(e) Atria

V. Put tick marks in appropriate boxes.

2. The membrane that surrounds the heart is called ...... .

SA Single Left Plasma Pulmonary node heart ventricle vein

3. Right side of the heart contains ...... blood. 4. Heart of fish pumps ...... blood, whereas the heart of bird pumps ...... blood.

Blood without corpuscles

5. Heart is largely composed of ...... muscles.

Fish

6. Valves prevent ...... flow of blood and are also present in ...... .

Pure blood

7. Cardiac cycle is divided into ...... and ...... phase.

Part of heart with the thickest wall

8. Crocodiles have ...... heart, but in turtles the heart is ...... . III. Mark the statements true(T) or false(F).

Pacemaker

1. Arteries are more muscular than veins.

F • ANSWERS • 8. four-chambered, transitional

A. 1. Right atrium 2. Lungs 3. Prevention of backflow of blood 4. Heart sends impure blood to lungs, and lungs sends back oxygenated pure blood to heart. 5. The heart with two chambers only, one atrium and one ventricle, is called single heart. 6. The heart with four chambers, two atria and two ventricles, is called double heart.

III. 1. T 2. F 3. F 4. F 5. F 6. F 7. T IV. (i)(c) (ii)(a) (iii)(e) (iv)(b) (v)(d) V. SA Single Left Plasma Pulmonary node heart ventricle vein Blood without corpuscles

7. The heart which has two atria and one ventricle (sometimes incompletely divided) is called transitional heart.

3

Fish

3

Pure blood

D. I. 1. (a), (b) 2. (a) 3. (d) 4. (b), (d) 5. (a), (c)

Part of heart with the thickest wall

6. (b) 7. (d) 8. (d) 9. (c) 10. (d) II. 1. thoracic 2. pericardial membrane 3. impure 4. deoxygenated, oxygenated 5. cardiac 6. back, heart 7. systolic, diastolic

3

Pacemaker

v

3 3

Foundation Sci Bio Class 10 151

Question Bank

151

4. Excretion (c) water content in urine would be higher (d) uric acid will not be excreted

A. Very-Short-Answer Questions 1. How does Hydra throw out excretory matter?

5. Correct route of the passage of urine is (a) collecting tubule—ureter—urinary bladder— urethra (b) convoluted tubule—loop of Henle—urinary bladder (c) ureter—urethra—urinary bladder (d) urethra—urinary bladder—ureter

2. Which part of haemoglobin is excreted with bile? 3. What is the process of artificial purification of blood called? 4. What are alkaloids? B. Short-Answer Questions 1. Describe the other excretory organs than kidneys in human beings.

6. Where does the pelvis of kidney lie? (a) In cortex (b) In medulla (c) In ureter (d) In urinary bladder

2. Write a short note on the different methods of excretion in plants. C. Long-Answer Questions

7. Mammalian kidney is (a) oval (c) bean shaped

1. Give an account of some excretory products of plants that are useful to man. 2. Describe how dialysis is carried out.

(b) cylindrical (d) trilobed

II. Fill in the blanks.

D. Objective Questions

1. The unit of kidney is called ...... .

I. Pick the correct option/options. More than one option may be correct.

2. The bunch of blood capillary in nephron is called ...... .

1. The unit of kidney is called (a) Bowman’s capsule (b) glomerulus (c) nephron (d) collecting tubule

3. The duct that emerges from kidney is called ...... . 4. ...... is the reabsorption of water to maintain the balance of water in human body.

2. Which is not the function of kidney? (a) Synthesis of urea (b) Excretion of urea (c) Reabsorption of water (d) Secretion

5. The dialyser works as kidney except ...... . III. Mark the statements true(T) or false(F).

3. The colour of urine is due to (a) phytochrome (b) cytochrome (c) haemochrome (d) urochrome

1. Kidney produces RBC. 2. Bowman’s capsule is the unit of kidney. 3. Distal convoluted tubule opens in the loop of Henle.

4. If the loop of Henle is abolished (a) tubular secretion will not take place (b) bile will not be excreted

4. Filtrate is hypotonic in proximal tubule. 5. Afferent arteriole brings blood to the nephron.

F • ANSWERS • A. 1. Hydra excretes through its mouth. 2. The pigment “haem”

II. 1. nephron 2. glomerulus 3. ureter 4. Osmoregulation 5. selective absorption

3. Haemodialysis

III. 1. F 2. F 3. F 4. T 5. T

4. A group of toxic waste products D. I. 1. (c) 2. (a) 3. (d) 4. (c) 5. (a) 6. (b) 7. (c)

v

5. Control and Coordination A. Very-Short-Answer Questions 1. Name the hormone which contains iodine.

7. Name the part of the brain which controls intelligence.

2. Name the hormone produced by the ovaries.

8. Name the part of the brain which controls involuntary action.

3. Name the phytohormone that inhibits growth.

9. Mention the number of cranial nerves.

4. Name the cells that produce insulin. 5. Specify the location of the olfactory lobe. 6. Specify the location of the pituitary gland.

B. Short-Answer Questions 1. Describe the effects of imbalance in the secretion of growth hormone.

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2. Describe chemotropism giving one example. 3. Describe the significance of the words positive and negative regarding tropism. 4. Describe the structure and function of islets of Langerhans. 5. Where is cerebrospinal fluid present and what is its function? 6. Describe any one function of spinal cord. C. Long-Answer Questions 1. Write an essay on pituitary gland and the hormones produced by it. 2. Write an essay on the dysfunction of thyroid gland. 3. Give an account of the function of adrenal gland. 4. Give detailed account of any two phytohormones. 5. Describe how tendrils twine around a support. 6. What does the nervous system of man consist of? 7. Give an account of the function of human brain. 8. Describe the mechanism of transmission of nerve impulse. D. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. Gigantism results from (a) growth hormone (b) thyroxine (c) adrenalin (d) testosterone 2. Goitre results from (a) gibberellin (b) iodine deficiency (c) calcium depletion (d) thyroid dysfunction 3. Secondary sexual characters are influenced by (a) thyroxine (b) adrenaline (c) testosterone (d) oestrogen 4. The hormone responsible for anger is (a) adrenaline (b) growth hormone (c) oestrogen (d) insulin 5. Which is/are correct correct about insulin? (a) It controls blood sugar. (b) It is produced by islets of Langerhans. (c) It is produced by parathyroid gland. (d) It is called the fight and flight hormone. 6. Plant growth is/are promoted by (a) cytokinin (b) auxin (c) gibberellin (d) abscisic acid

7. Which of the following is/are not due to hormone? (a) Diabetes (b) Arthritis (c) Gigantism (d) Reflex action 8. The fluid that lies above and below the meninges of the brain is called (a) lymph (b) serum (c) plasma (d) cerebrospinal fluid 9. Which is a correct statement? (a) Olfactory lobes and optic lobes lie in the same region. (b) Cranium is covered by cerebrospinal fluid. (c) Cerebrum controls intelligence. (d) Cerebellum controls intelligence. 10. Grey matter is (a) a fluid (b) cluster of cytons (c) a hormone (d) a network of blood vessel 11. Pineal gland is situated on the (a) dorsal surface of the hindbrain (b) dorsal surface of the forebrain (c) ventral surface of the midbrain (d) ventral surface of the forebrain 12. Medulla oblongata is (a) a part of the forebrain (b) a part of the midbrain (c) a part of the hindbrain (d) last part of the hindbrain 13. Synaptic terminal is the end of (a) cyton (b) dendrite (c) axon (d) none of the above 14. Gustatoreceptors lie (a) on the tongue (b) in the nose (c) in the ear (d) in the eyes 15. Reflex arc is formed by (a) ventral sensory nerve and dorsal motor nerve (b) dorsal sensory nerve and ventral motor nerve (c) neither of the above (d) both (a) and (b) II. Fill in the blanks. 1. The pituitary gland lies on ...... . 2. The thymus gland is ...... in children. 3. The cells of the islets of Langerhans produce ...... . 4. ...... is plant’s response to contact with hard surface. 5. ...... is the master gland.

Foundation Sci Bio Class 10 153

Question Bank

6. ...... and ...... protect the brain of mammals.

153

6. Sensory nerve connects the dorsal root of the spinal cord.

7. Cerebellum is the centre of ...... action and cerebrum controls ...... .

IV. Match the columns.

8. In a nerve cell, ...... receive the stimulus and ...... transmits the impulse.

A

B

(i) Diencephalon

(a) Coordinating cerebellum and cerebrum

1. Ovaries produce only one hormone.

(ii) Spinal nerves

(b) Rapid loss of water

2. Testosterone produces femaleness.

(iii) Algesireceptors

(c) Apical meristem

3. Parathormone is produced by adrenal gland.

(iv) Pons

(d) Controls hunger, thirst

(v) Auxin

(e) Feeling of pain

(vi) Turgor change

(f) 31 pairs

III. Mark the statements true(T) or false(F).

4. Human brain and spinal cord are solid. 5. Spinal cord arises from the medulla.

• ANSWERS • A. 1. Thyroxine

11. (b) 12. (d) 13. (c) 14. (a) 15. (b)

2. Oestrogen 3. Abscisic acid

6. Attached to the diencephalon in cerebrum

1. diencephalon 2. present 3. insulin 4. Thigmotropism 5. Pituitary 6. Cranium, meninges 7. involuntary, intelligence

7. Cerebrum

8. dendrons, axon

II.

4. A cluster of cells called islets of Langerhans 5. Cerebrum

D.

8. Medulla oblongata

9. 12

I. 1. (a) 2. (b), (d) 3. (c), (d) 4. (a) 5. (a), (b)

III. 1. F 2. F 3. F 4. F 5. T 6. T

6. (a), (b), (c) 7. (b), (d) 8. (d) 9. (c) 10. (b)

IV. (i)(d) (ii)(f) (iii)(e) (iv)(a) (v)(c) (vi)(b)

v

6. Reproduction A. Very-Short-Answer Questions

19. Write down the function of seminal vesicle.

1. Give an example where multiple fission is found.

20. What is the meaning of gestation period?

2. Give two examples where spore formation is the common mode of reproduction.

21. What is the meaning of parturition?

3. Name the male and female reproductive organs of a flower. 4. Why are petals brightly coloured? 5. Where are pollen grains produced? 6. Where is ovary located in a plant?

B. Short-Answer Questions 1. As compared to dry slice of bread, bread moulds grow luxuriently on a moist slice of bread. Why? 2. If a Spirogyra filament is broken into two pieces, what will be the result?

8. Where do pollen grains germinate?

3. If in a flowering plant, the male gametes have 8 chromosomes, what will be the chromosome number of the zygote and the plant itself?

9. Where is zygote present in the flower after fertilization?

4. The bisexual flower produces fruit even if stamens are removed before pollination. Why?

7. Give two examples where self-pollination takes place.

10. What does an embryo in a plant contain? 11. When does embryo germinate? 12. Where are sperms produced? 13. Name the protective covering of testes. 14. Where are ova produced? 15. What is umbilical cord? 16. What is the importance of tubectomy? 17. Describe the parts of a sperm. 18. What is the reproductive organ of a male flower?

5. Why do colonies of yeast multiply in sugar solution but not in water? 6. Collect information about the chromosome numbers of four common plants and four common animals from your school library and correlate the following: (i) number of chromosomes and the size of the organisms (ii) number of chromosomes and the rate of reproduction (iii) number of chromosomes and the complexity of the organisms

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7. Is there any possibility of fertilization without pollination in a flower? Explain with reason.

5. Discuss the functions of different whorls of a flower.

8. Is cell division a type of reproduction? Explain.

6. In human beings, fertilization can take place once in a month. Explain whether it is true.

9. How does chromosome number remain constant in zygote, embryonic cells and adult individuals?

7. Discuss the statement that reproduction is essential for the stability of a species.

10. What is the reason behind the remarkable similarities among offspring produced after asexual reproduction? 11. Differentiate between sexual maturation general growth of an individual.

8. How does fertilization take place in human beings? What changes will be exhibited after fertilization?

and

9. Give an account of female reproductive system in human beings.

12. Are chromosome numbers of parents and offspring the same? Explain how it is so.

10. Give an account of male reproductive system in human beings.

13. How is reproduction linked to the stability of population of a species? Explain.

11. Discuss different types of vegetative propagation.

14. Is there any genetic difference between sperm and egg? What will be the ratio of chromosome number between a sperm and a zygote? 15. Mention the glands and their functions associated with male reproductive system. What will be the path of sperm during ejaculation? 16. Mention the changes taking place in the uterus after the implantation of young embryo.

12. Explain the mechanism implantation. 13. Discuss the reproduction.

role

of

of

fertilization

hormones

human

14. Why is sexual mode of reproduction superior to asexual mode? D. Crossword Puzzle 1

17. Why are mechanical barriers used during sexual act?

3

18. What is placenta? What is its role? 19. Define self-pollination.

in

and

5

2

20. Define cross-pollination. 21. What is the function of calyx. 4

22. Why do wind-pollinated flowers produce light pollen grains? 23. Write a short note on artificial modes of vegetative propagation.

6

24. What is the difference between self-pollination and cross-pollination? 25. How is embryo formed? 26. Describe the structure of the ovary in a plant. 27. Define puberty. 28. How is ovum released from the ovary? 29. What will be the characteristics of the seminal fluid of a vasectomised person? 30. Explain the importance development of embryo.

of

uterus

in

the

31. Define vasectomy. C. Long-Answer Questions 1. Differentiate between asexual reproduction and sexual reproduction. Why does sexual reproduction result in variations among offspring?

Down 1. Transfer of pollen grains from the anther to the stigma 3. The muscular lower portion of the uterus 5. The zygote develops into a baby here Across 2. A disclike organ through which the embryo absorbs food and oxygen

2. Why are fragmentation, spore formation, fission and budding considered asexual reproduction?

4. Female reproductive organ producing gamete, in both plants and animals

3. What are the differences between gametes and zygote? How do they help during sexual reproduction?

6. The outermost whorl protecting the floral whorls in the bud stage

4. Differentiate between pollination and fertilization. What happens in a flower after fertilization?

E. Diagrammatic Questions 1. Draw labelled diagrams to show budding in Hydra.

Foundation Sci Bio Class 10 155

Question Bank

2. Draw diagrams to demonstrate binary fission in Amoeba. 3. Draw a neat diagram of a flower and label different parts. 4. With the help of a clean diagram show the path of pollen tube from stigma to ovary. 5. Draw a labelled diagram of male sex organs of human beings. 6. Draw a clean diagram of female sex organs of human beings and label different parts related to the following: (i) Entry of sperms (ii) Site of fertilization (iii) Site of implantation (iv) Production of egg F. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. In vegetative propagation, new plants are produced from (a) root, stem and flowers (b) root, stem and seeds (c) root, stem and leaves (d) root, leaves and flowers 2. The example of multiple fission (ability of a cell to divide into many daughter cells) is seen in (a) Hydra (b) Plasmodium (c) Paramoecium (d) Spirogyra 3. Which of the following structures is responsible for transmission of characters from parents to offspring? (a) Centrosome (b) Ribosome (c) Cytoplasm (d) Genes 4. Which of the following organisms reproduce through asexual means? (a) Goat (b) Yeast (c) Dog (d) Banana 5. Fragmentation (breaking up of filaments into smaller pieces) is the common method of asexual reproduction in (a) yeast (b) Spirogyra (c) Amoeba (d) Plasmodium 6. Which of the following statements is common for Hydra, yeast, Spirogyra and Amoeba? (a) They are unicellular. (b) They are multicellular. (c) They reproduce asexually. (d) They cannot multiply.

155

9. Which of the following factors is/are responsible for rapid spread of Rhizopus (bread mould) on bread? (a) Presence of round-shaped sporangia (b) Formation of numerous spores (c) Availability of moisture in bread (d) Availability of nutrients in bread 10. Why is reproduction essential for living organisms? (a) To maintain growth (b) To maintain number (c) To continue the species from generation to generation (d) To provide variations 11. The chromosome number in parents and offspring of a particular species remains constant due to (a) halving of chromosome number during gamete formation (b) doubling of chromosome number during gamete formation (c) doubling of chromosome number after gamete formation (d) multiplication of chromosomes during gamete formation 12. Why do offspring formed by asexual reproduction look very similar among themselves? (a) Because asexual reproduction is a common method of reproduction (b) Because asexual reproduction takes place after maturing of individuals (c) Because asexual reproduction involves one parent and does not involve gametes (d) Because asexual reproduction takes place in all the conditions 13. The characters that are transmitted from parents to offspring exhibit (a) only variations (b) only similarities (c) both variations and similarities with parents (d) mixed and independent characters 14. Sexual reproduction results in more variations in the offspring because (a) genetic material comes from many parents (b) genetic material is brought from two different species (c) genetic material comes from two parents of the same species (d) it is a long process involving two parents 15. Which of the following statements are true?

7. Rhizopus and Mucor reproduce mainly by (a) producing spores (b) producing buds (c) fragmentation (d) multiple fission

(b) Gametes fuse to form zygote.

8. The tubular threadlike structures bearing sporangia at their tips in Rhizopus are called (a) roots (b) rhizoids (c) hyphae (d) filaments

(c) Offspring formed after sexual reproduction are similar to each other. (d) DNA from two different individuals are combined during sexual reproduction.

(a) Gametes are reproduction.

formed

during

sexual

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16. The male and female gamete-producing organs of a flower is called (a) ovary and ovule (b) stamen and anther (c) stigma and stamen (d) anther and ovary 17. Which of the following do not represent the correct sequence of reproductive stages? (a) Zygote ® Gametes ® Embryo ® Seedling (b) Gametes ® Zygote ® Embryo ® Seedling (c) Gametes ® Zygote ® Seedling ® Embryo (d) Gametes ® Embryo ® Seedling ® Zygote 18. Which of the following sequence of events do not represent the correct sequence of sexual reproduction in higher plants? (a) Pollination ® Embryo formation ® Fertilization (b) Embryo formation ® Pollination ® Fertilization (c) Embryo Formation ® Fertilization ® Pollination (d) Pollination ® Fertilization ® Embryo formation 19. Which of the following statements are correct? (a) Bisexual flowers contain either stamen or pistil. (b) Unisexual flowers contain either stamen or pistil. (c) Bisexual flowers possess both stamen and pistil. (d) Unisexual flowers exhibit cross-pollination. 20. Choose the correct statements among the following. (a) Flowers always have both the sex organs. (b) Flowers are the reproductive organs of the plants. (c) All plants bear flowers. (d) Flowers give rise to fruit after fertilization. 21. Pollen tube grows out of pollen grain and reaches the ovary finally through (a) anther (b) stigma (c) germ cell (d) style

25. The following figure shows (a) binary fission in Hydra (b) budding in yeast (c) fragmentation in Hydra (d) budding in Hydra

26. The following diagram represents (a) budding in Hydra (b) fragmentation in Spirogyra (c) binary fission in Spirogyra (d) budding in yeast

22. Length of pollen tube exhibits the distance from (a) pollen grain to stigma (b) pollen grain to style (c) pollen grain through the style to the ovule (d) stigma to style 23. The following figure represents (a) fragmentation (b) binary fission (c) multiple fission (d) budding

Nucleus

Daughter cells

24. Which of the following processes is represented in the following figure? (a) Multiple fission (b) Binary fission (c) Sporulation (d) Vegetative propagation

27. In the following figure the parts A, B, C and D are sequentially (a) stigma, anther, petal and pistil (b) anther, pistil, petal and stigma (c) anther, petal, pistil and stigma (d) stigma, anther, pistil and petal

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157

31. Which of the following changes occurs during adolescence in boys? (a) Cracking of voice (b) Increase in weight (c) Breakage of milk teeth (d) Increase in height 32. Which of the following represents the correct sequence of organs for transport of sperms in man? (a) Ureter ® Testis ® Urethra (b) Vas deferens ® Urethra ® Testis (c) Testis ® Vas deferens ® Urethra (d) Testis ® Ureter ® Urethra 28. In the following figure parts A, B, and C represent (a) radicle, plumule and cotyledons respectively (b) plumule, radicle and cotyledons respectively (c) radicle, cotyledons and plumule respectively (d) cotyledons, plumule and radicle respectively

33. Why does testes lie in the scrotum outside the body cavity in human males? (a) Because it helps in transfer of gametes (b) Because it helps in storage of sperms (c) Because it helps in mating (d) Because it helps in formation of sperm 34. Sperms from the testis pass through (a) urinary bladder (c) scrotum

(b) vas deferens (d) prostate gland

35. Which of the following functions are not related to testes? (a) Formation of placenta (b) Secretion of male hormone (c) Formation of male gametes (d) Secretion of oestrogen

29. In the following figure parts A, B and C represent (a) stigma, pollen tube and ovary wall respectively (b) stigma, pollen grain ad ovule respectively (c) pollen grain, pollen tube and ovary wall respectively (d) pollen grain, ovary and pollen tube respectively

36. The reproductive organs in human females include (a) ovary, uterus, testis and vagina (b) uterus, vagina, prostate gland and urethra (c) ovaries, Fallopian tubes, uterus and vagina (d) ovaries, uterus, vagina and scrotum 37. An event that represents the onset of reproductive phase in human females is called (a) adolescence (b) menstruation (c) implantation (d) fertilization 38. The process by which embryo gets embedded in the wall of the uterus is called (a) implantation (c) menstruation 39. What are the means unfavourable conditions? (a) Budding (c) Spore formation

(b) adolescence (d) parturition of

reproduction

in

(b) Multiple fission (d) Fragmentation

40. Which of the following does not occur in the female? (a) Prostate gland (b) Urethra (c) Uterus (d) Vas deferens

30. Which of the following diseases is/are transmitted through sexual contact? (a) AIDS (b) Gonorrhoea (c) Syphillis (d) Hepatitis

41. What is applicable with respect to the Fallopian tube? (a) The embryo is implanted here. (b) It is ligated in vasectomy. (c) Fertilization occurs here. (d) Oestrogen is secreted from here.

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13. Sperm formation requires ...... temperature than the normal body temperature.

42. Where does cervix lie in the female? (a) Above the vagina (b) Above the uterus (c) Below the Fallopian tube (d) Behind the ovary

14. The ...... forms a common passage for both the sperms and urine.

43. Which organ(s) lie(s) outside the abdominal cavity? (a) Testis (b) Seminal vesicle (c) Prostate gland (d) Penis 44. Sperms are produced in (a) the penis (c) the prostate gland

(b) the vas deferens (d) none of the above

45. The female sex organ of a flower consists of (a) sepals (b) pollen sacs (c) ovary (d) stigma

15. The egg is carried from the ovary to the womb through ...... . 16. Sperms travel upwards and reach the ...... where they may fuse with the egg. 17. The ...... prepares itself every month to receive and nurture the growing child. 18. Placenta is embedded in the ...... wall. 19. The development of the child inside the mother’s body takes approximately ...... . 20. ...... is the result of non-fertilization of egg.

46. Parturition occurs (a) before gestation (b) after gestation (c) before implantation (d) during menstruation

21. The embedding of embryo in the wall of the uterus is called ...... . 22. The embryo is connected to the ...... by ...... . 23. Gonorrhoea is caused by ...... .

47. Conception occurs (a) before ovulation (b) after ovulation when sperm is not there (c) after ovulation when sperm fertilizes the ovum (d) when the ovum lies in the ovary

24. Mechanical barriers do not allow ...... between sperm and egg.

48. Which one is due to bacterial infection? (a) AIDS (b) Gonorrhoea (c) Cancer in cervix (d) Tumour in ovary

III. Write Yes/No.

25. Both vasectomy and tubectomy ensure that ...... will not take place.

1. Will the process of copying DNA have some variations each time?

49. What is contraception? (a) Promotion of conception (b) Promotion of sterility (c) Prevention of conception (d) None of the above

2. Is variation unimportant for the survival of species over time?

II. Fill in the blanks.

5. Is regeneration a common feature in Planaria?

1. Small fragments of ...... filament grow into new individuals.

6. Can we say that grafting is not useful for agriculture?

2. Hydra reproduce commonly by ...... .

7. Are plants produced by vegetative reproduction genetically similar?

3. Is multiple fission common in Plasmodium? 4. Does Spirogyra reproduce by any other means than fragmentation?

3. Plants raised by ...... can bear flowers and fruit earlier than those produced from seeds. 4. All plants produced by vegetative propagation are ...... similar. 5. The spores of Rhizopus are covered by ...... that protect them until they come into contact with moist surface. 6. Pollen grains are produced in ...... .

8. Is spore formation the common method of sexual reproduction in Rhizopus? 9. Do DNA from two different individuals combine during sexual reproduction? 10. Can stamens and petals be called reproductive parts of a flower?

7. The terminal part of carpel is called ...... .

11. Does the ovule fertilization?

8. Pollen tube reaches the ovary through ...... .

12. Is fruit formed from ovary?

9. After ...... the zygote divides several times to form an ...... within the ovule.

13. Is the period during adolescence called puberty?

10. The ovule gradually develops into a ...... . ......

from

into

seed

before

14. Do testes secret testosteron? 15. Is an egg produced daily by one of the ovaries in human beings?

11. The period during ...... is called puberty. 12. During sexual reproduction individuals fuse.

develop

two

16. Is it true that bacterial diseases are not transmitted through sexual act?

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Question Bank

IV. Mark the statements true (T) or false (F). 1. Binary fission is the simplest method of sexual reproduction. 2. Buds may be unicellular or multicellular. 3. If Planaria is cut into pieces, each piece can regenerate into an entire individual. 4. The stamens are collectively called gynoecium. 5. The radicle forms the shoot while the plumule forms the root. 6. The prostate gland adds its secretion to the seminal fluid. 7. A fertilized ovum develops into a baby inside the uterus. 8. The period of menstruation usually lasts for nine months. 9. AIDS is a bacterial infection. 10. Gonorrhoea and syphilis are common sexually transmitted bacterial diseases. 11. Oral pills do not disturb hormonal balance in human body. 12. Surgical methods are safe contraceptive methods. 13. Surgery can be used for removal of unwanted pregnancies. 14. Implantation of embryo occurs in uterus. 15. Fertilization occurs in the Fallopian tube. 16. Vasectomised male will not ejaculate. 17. Seminal vesicle secretes sperms.

159

V. Match the columns 1.

A

B

(i) Budding (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii)

2.

Rhizopus Pistil Sexual reproduction Copper-T Ovary of a flower Fertilized egg Amoeba Grafting Planaria Unisexual flower Plasmodium

(a) Mechanical barrier (b) Fruit (c) Binary fission (d) Cross-pollination (e) Regeneration (f) Vegetative reproduction (g) Multiple fission (h) Spore formation (i) Hydra (j) Zygote (k) Gametes (l) Female reproductive part of a flower

A

(i) (ii) (iii) (iv) (v)

Testis Vas deferens Condom IUCD

Cervix

B

(a) (b) (c) (d) (e)

Sperm duct Scrotal sac Contraception Lower part of vagina Prevention of STD

• ANSWERS • A. 1. Multiple fission is found in Chlorella.

16. Tubectomy prevents the passage of ova down the Fallopian tube, thus ensuring fertilization does not happen.

2. Rhizopus(bread mould) and Mucor reproduce by spore formation. 3. Male and female reproductive organs of a flower are androecium and gynoecium, respectively.

17. The sperm has a head and a tail. 18. Androecium

4. Brightly coloured petals attract insects and so help in pollination.

19. Seminal vesicle stores sperms and secretes semen.

5. Pollen grains are produced in anthers.

20. The time from fertilization to birth, i.e., the total period of embryonic development, is gestation period.

6. Ovary in a plant is located at the base of carpel in gynoecium. 7. Self-pollination takes place in pea and Hibiscus.

21. The expulsion of baby from the uterus by the contraction of uterine muscles is parturition, or birth.

8. Pollen grains germinate on the stigma. 9. After fertilization zygote is present inside the ovule.

D.

10. The embryo contains plumule, radicle and cotyledons.

F.

11. The embryo germinates when it finds favourable environmental condition. 12. Sperms are produced in the testes. 13. Testes are protected by the scrotum. 14. Ova are produced in the ovaries. 15. The tube that connects the embryo and the placenta is the umbilical cord.

Down: 1. Pollination 3. Cervix 5. Uterus Across: 2. Placenta 4. Ovary 6. Calyx I.

1. (c) 2. (b) 3. (d) 4. (b), (d) 5. (b) 6. (c) 7. (a) 8. (c) 9. (b), (c), (d) 10. (c) 11. (a) 12. (c) 13. (c) 14. (c) 15. (a), (b), (d) 16. (d) 17. (a), (c), (d) 18. (a), (b), (c) 19. (b), (c), (d) 20. (b), (d) 21. (d) 22. (c) 23. (b) 24. (a) 25. (d) 26. (b) 27. (b) 28. (d) 29. (c) 30. (a), (b), (c) 31. (a), (b), (d) 32. (c) 33. (d) 34. (b) 35. (a), (d) 36. (c) 37. (b) 38. (a) 39. (b), (c) 40. (a), (d) 41. (c) 42. (a) 43. (a), (d) 44. (d) 45. (c), (d) 46. (b) 47. (c) 48. (b) 49. (c)

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II.

1. Spirogyra 2. budding 3. vegetative propagation 4. genetically 5. thick walls 6. stamen 7. stigma 8. style 9. fertilization, embryo 10. seed 11. adolescence 12. germ cells 13. lower 14. urethra 15. Fallopian tube 16. oviduct 17. uterus 18. uterine 19. nine months 20. Menstruation 21. implantation 22. placenta, umbilical cord 23. bacteria 24. fusion 25. fertilization

III.

1. Yes 2. No 3. Yes 4. No 5. Yes 6. No 7. Yes 8. No 9. Yes 10. Yes 11. No 12. Yes 13. Yes 14. Yes 15. No 16. No

IV.

1. F 2. T 3. T 4. F 5. F 6. T 7. T 8. F 9. F 10. T 11. F 12. T 13. T 14. T 15. T 16. F 17. F

V.

1. (i)(i) (ii)(h) (iii)(l) (iv)(k) (v)(a) (vi)(b) (vii)(j) (viii)(c) (ix)(f) (x)(e) (xi)(d) (xii)(g) 2. (i)(b) (ii)(a) (iii)(e) (iv)(c) (v)(d)

v

7. Heredity and Evolution A. Very-Short-Answer Questions 1. 2. 3. 4. 5.

Define allele. When does duplication of DNA take place? Name the book in which Lamarckism is mentioned. Name the book in which Darwinism is described. Who gave the first scientific theory of organic evolution? 6. Who gave the first modern theory of organic evolution? B. Short-Answer Questions 1. Differentiate between dominant and recessive characters. 2. What do you understand by the law of independent assortment? 3. What do you understand by the law of segregation? 4. Which law of Lamarck was disproved and how? 5. In what respect is Darwinism deficient? C. Long-Answer Questions 1. Write an essay on Mendelism. 2. Explain the law of use and disuse given by Lamarck. 3. Explain how Lamarckism is different from Darwinism. 4. Write a short note on molecular phylogeny. 5. Why is variation considered to be the raw material of organic evolution? Explain. D. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. Heredity refers to (a) passing of characters from parents to offspring (b) sterility (c) the study of the pattern of passing of characters (d) none of the above 2. Heredity is opposed by (a) variation (b) environment (c) genes (d) none of the above 3. Variations may be due to (a) mutation (b) environmental factors

(c) cell division (d) all of the above 4. Mendel was (a) an Englishman (c) a German

(b) an American (d) an Austrian

5. What was used by Mendel for his experiments? (a) Fruit flies (b) Pea plant (c) Rice plant (d) Rabbits 6. What does a dominant character mean? (a) It is expressed first. (b) It suppresses the recessive character. (c) It remains unaffected by the recessive character. (d) All of the above 7. What is an allele? (a) A gene (c) RNA

(b) A protein (d) None of the above

8. In a monohybrid cross done by Mendel (a) F1 had 75% tall plants and 25% dwarf plants (b) F1 had all tall plants (c) F1 had all dwarf plants (d) none of the above was observed 9. Which is correct about autosomes? (a) They contain genes for sexual characters. (b) They contain genes for both sexual and vegetative characters. (c) They contain genes for vegetative characters. (d) None of the above 10. What is applicable for Y chromosomes? (a) They lack DNA. (b) They lack histones. (c) They contain genes for maleness. (d) They contain genes for femaleness. 11. Struggle for existence was explained by (a) Lamarck (b) Hugo de Vries (c) Charles Darwin (d) none of the above 12. Inheritance of acquired characters refers to (a) inheritance of adaptive and nonadaptive characters (b) inheritance of somatic characters as well (c) inheritance of germinal variations (d) none of the above

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Question Bank

13. Gene mutation means (a) change in base pairs of the gene (b) addition of a base pair in the gene (c) removal of a base pair in the gene (d) all of the above

161

III. Mark the statements true(T) or false(F). 1. Mutation can occur due to X-rays. 2. Vestigial organs are nonfunctional. 3. Genes do not maintain their purity, said Mendel.

14. Who was not involved in the study of the origin of life? (a) Miller (b) Urey (c) Morgan (d) Oparin

4. Genes assort independently. 5. Most mutations are beneficial. 6. Struggle for existence is always active. 7. Nature selects favourable characters and eliminates unfavourable ones.

15. What is meant by gene flow? (a) Floating of genes (b) Exchange of genetic material (c) Melting of genes (d) None of the above

IV. Match the columns. A

16. Which of the following constitutes an example of Homologous organs? (a) Wings of bat and wings of butterfly (b) Forelimbs of horse and wings of bat (c) Eyes of insects and eyes of man (d) Legs of cockroach and hindlegs of frog II. Fill in the blanks. 1. Allele is another name of ...... . 2. DNA is hereditary material because it is ...... and ...... .

B

(i) Natural selection

(a) Lamarck

(ii) Inheritance of acquired characters

(b) Phenotype

(iii) Homozygous condition

(c) Darwin

(iv) Physical traits

(d) Molecular phylogeny

(v) Study of DNA sequence

(e) TT

V. Put tick marks in appropriate boxes. Mutation Evolution Genotype Palaeontology theory

3. Mutation is generally ...... to animals. 4. Genes that are not expressed are called ...... .

Genetic constitution

5. According to Darwin the power of reproduction is ...... and this will lead to ...... for food and shelter.

Analogous organs

6. In a monohybrid cross, one of the alleles is ...... and another, ...... .

Hugo de Vries

7. The real source of variation is ...... .

Study of fossils

8. As it stands today, characters ...... are not inherited, and in this regard theory of ...... is not sustainable.

• ANSWERS • A. 1. Unit factor responsible for genetic character, named by Mendel 2. Just before cell division

III.

1. T 2. T 3. F 4. T 5. T 6. T 7. T

IV.

(i)(c) (ii)(a) (iii)(e) (iv)(b) (v)(d)

V.

3. Philozophie Zoologique 4. Origin of Species 5. Lamarck D. I.

II.

1. (a) 7. (a) 13. (d)

Mutation Evolution Genotype Palaeontology theory

6. Darwin

2. (a) 8. (b) 14. (c)

3. (d) 4. (d) 5. (b) 6. (d) 9. (c) 10. (c) 11. (c) 12. (b) 15. (b) 16. (b)

Genetic constitution

3

Analogous organs

1. gene 2. replicated, transmitted 3. beneficial

Hugo de Vries

4. recessive 5. enormous, struggle 6. dominant, recessive 7. mutation

Study of fossils

8. acquired, Lamarck

v

3 3 3

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8. Our Environment A. Very-Short-Answer Questions 1. Give a scientific term for each of the following: (a) The component which includes physical environment, nutrients and climatic factors (b) The physical and biological world where the organisms live (c) Organisms which eat both plants and flesh of other animals (d) A position in a food chain (e) Accumulation of chemicals trophic levels of a food chain

at

successive

10. Why can the pesticides not be removed from food grains by washing? 11. What are the effects of ozone-layer depletion on human beings? 12. Why is improper disposal of waste harmful to environment? 13. Suggest some measures to replace commonly used nonbiodegradable products with biodegradable ones. C. Long-Answer Questions 1. Differentiate between food chain and food web with one example.

(f) Organisms which obtain food from other living organisms

2. Define decomposers. Explain their role in an ecosystem.

2. Why do herbivores occupy a position next to producers in a food chain?

3. Why is the flow of energy unidirectional? Explain it with the 10% law of transfer of energy.

3. Give one example each of herbivore, carnivore and omnivore. 4. Do microorganisms like bacteria play any role in an ecosystem?

4. Categorize some of your daily activities as ecofriendly. Suggest some more ecofriendly activities which we should adopt in day-to-day life.

5. Why do only autotrophs capture the energy present in the sunlight?

5. Discuss different biotic components and their importance in an ecosystem.

6. Why is straight line food chain not common in the natural ecosystem?

6. Describe those agricultural practices which are harmful for environment.

7. Fertilizers and pesticides are used in the soil. How do they reach the food grains and vegetables?

7. Divide the wastes generated from your house into biodegradable and nonbiodegradable categories and suggest methods for their disposal.

8. What is the position of human beings in any food chain?

8. How do industrial wastes affect our environment? 9. Discuss possible methods to manage garbage and sewage.

9. What is the main function of ozone layer of the atmosphere? 10. Name the chemical which is mainly responsible for ozone-layer depletion.

D. Crossword Puzzle 3

11. Where are CFC found? 12. What is UNEP agreement of 1987?

5

B. Short-Answer Questions

2

1. What is a food chain? Write the common food chain of a pond ecosystem. 2. We should carry cloth bags every time we go to the market. Why?

1

3. What are the abiotic components in an ecosystem? 4. What are the differences between consumers and secondary consumers?

4

primary

5. Why does a food chain always begin with producers? 6. What positions do producers, herbivores and carnivores occupy in a food chain? 7. What is ten per cent law of energy transfer? 8. How does the concentration of pesticides and fertilizers increase in the water bodies? 9. Why do we consider crop fields as artificial ecosystems?

Down 1. Common nonbiodegradable substance 3. Organism which breaks down complex compounds into simpler ones 5. Organism depending on other organism for food

Foundation Sci Bio Class 10 163

Question Bank

Across 1. Photosynthetic plant 2. Gaseous layer which protects us from ultraviolet rays 4. The flow of ...... is unidirectional. E. Diagrammatic Questions 1. Draw diagrams to represent a common food chain in a grassland ecosystem. 2. With the help of flow charts show a food web operating in an ecosystem. 3. Draw a diagram to represent pyramid of numbers in any ecosystem. 4. With the help of diagrams explain how ozone layer gets depleted by CFC. 5. Draw a pond ecosystem showing its different components. F. Objective Questions I. Pick the correct option/options. More than one option may be correct. 1. An ecosystem consists of (a) nonliving things only (b) living organisms only (c) both living and nonliving things (d) water, gases and soil 2. Chlorofluorocarbons (CFCs) are mainly responsible for (a) global warming (b) acid rain (c) biomagnification (d) ozone-layer depletion 3. Which of the following effects on humans will be caused by excessive exposure to UV-rays? (a) Skin cancer (b) Damage to immune system (c) Damage to heart and lungs (d) Peptic ulcers 4. Choose the correct statement(s). (a) Green plants convert solar energy into chemical energy. (b) Substances that are broken down by biological processes are nonbiodegradable. (c) DDT and plastic are nonbiodegradable. (d) Producers synthesize food from inorganic compounds. 5. Which trophic level is occupied by carnivores in a food chain? (a) First (b) Second (c) Third (d) Fourth 6. If a frog eats a grasshopper, then the energy will be transferred from (a) (b) (c) (d)

consumer to producer primary consumer to secondary consumer secondary consumer to primary consumer secondary consumer to tertiary consumer

163

7. If 10 kilocalories of energy is available to snakes (fourth trophic level), what will be the available energy at producer level in the following food chain? Grass ® Grasshopper ® Frog ® Snake (a) 100 kilocalories (b) 1000 kilocalories (c) 1 kilocalory (d) 10,000 kilocalories 8. A network of interconnected food chains is called (a) ecological pyramid (b) food web (c) ecosystem (d) trophic level 9. Which of the following groups of organisms do not synthesize carbohydrates from solar energy and inorganic compounds? (a) Producer (c) Consumers

(b) Herbivores (d) Decomposers

10. Which of the following represents an artificial ecosystem? (a) Forest (b) Grassland (c) Lake (d) Crop field 11. Why should we not use plastic cups and plates? (a) Because they are costly. (b) Because they are biodegradable. (c) Because they are very light. (d) Because they are nonbiodegradable. 12. Which of the following groups of organisms convert organic materials to inorganic forms? (a) Producers (b) Consumers (c) Decomposers (d) Green plants 13. What will be the result if in the following food chain goat population is decreased considerably? Green plant ® goat ® Lion (a) Green plants will die. (b) The population of lion will increase. (c) The population of green plants will increase and the lion population will decrease. (d) Lion will start consuming green plants. 14. In which form is the 10% energy available for transfer from one trophic level to the next in an ecosystem? (a) Light energy (b) Mechanical energy (c) Heat energy (d) Chemical energy 15. Why is the number of trophic levels limited in a food chain? (a) Because there is increase in energy at each level. (b) Because there is succesive decrease in energy at higher trophic levels. (c) Because trophic levels are connected. (d) Because producers constitute first trophic level. 16. What percentage of solar radiation is absorbed by all the green plants for photosynthesis? (a) 0.1% (b) 1% (c) 10% (d) 100%

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Foundation Science: Biology for Class 10

17. In the following diagram which trophic level will have the maximum energy? (a) T1 (b) T 2 (c) T 3 (d) T 4

6. Human beings occupy the ...... position in any food chain. 7. The ozone at the higher levels of atmosphere is a product of UV radiations acting on ...... molecule. 8. The various components of an ecosystem are ...... . 9. There is ...... of energy when we go from a trophic level to the next trophic level. 10. Human activities have an impact on the ...... . 11. A position in a food chain is called a ...... .

18. What does the following diagram represent? (a) Pyramid of energy (c) Pyramid of number

(b) Pyramid of biomass (d) Biomagnification

12. A series of interconnected food chains representing the feeding relationship of the organisms within an ecosystem is called ...... . 13. The top ...... is not killed and eaten by other animals of the ecosystem. 14. In a grassland ecosystem a hawk represents the ...... . 15. The substances formed in decomposition are released into the ...... and the ...... . 16. ...... wastes can be broken down into simpler substances by decomposers. 17. The ultimate source of energy in an ecosystem is the ...... . 18. Producers always contain ...... pigments. III. Write Yes/No. 1. Does an ecosystem consist of abiotic components?

19. Omnivores are one type of (a) producers (c) decomposers

(b) consumers (d) abiotic component

20. Bacteria and fungi do not act as (a) producers (c) autotrophs

(b) consumers (d) decomposers

21. The herbivores are not (a) consumers (c) producers

(b) decomposers (d) autotrophs

22. Organisms which feed on dead plants and animals are called (a) consumers (c) decomposers

(b) producers (d) heterotrophs

II. Fill in the blanks. 1. Substances that are broken down by biologial processes are called ...... . 2. Gardens and ...... are artificial ecosystems. 3. ...... constitute the first trophic level. 4. Autotrophs capture the energy present in sunlight and convert it into ...... . 5. The flow of energy is ...... .

both biotic and

2. Do gardens represent artificial ecosystem? 3. Are living plants and animals decomposed by decomposers? 4. Are herbivores, carnivores classifications of consumers?

and

omnivores

5. Do autotrophs constitute the first trophic level in an ecosystem? 6. Are herbivores the secondary consumers? 7. Can the flow of energy be bidirectional? 8. The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight. Is it true? 9. Can we say that there is progressive increase in energy level in successive trophic levels? 10. Does the accumulation of nonbiodegradable pesticides in food chain result in biological magnification? 11. Is it true that ozone, the deadly poison it is, shields the surface of the earth from UV radiation? 12. Do carnivores that feed upon herbivores belong to the second trophic level?

Foundation Sci Bio Class 10 page 165

Question Bank

165

V. Match the columns.

IV. Mark the statements true (T) or false(F). 1. Forests are artificial ecosystems.

A

2. All animals which eat plants or other animals are consumers. 3. The frog that eats the grasshopper is a secondary consumer. 4. Decomposers are also called saprotrophs. 5. Energy and materials are not transferred from one trophic level to another. 6. DDT is a nonbiodegradable substance.

B

(i) Biotic components

(a) Metals

(ii) Garden

(b) Abiotic component

(iii) Nonbiodegradable substance

(c) Carnivore

(iv) Decomposers

(d) Snake

(v) Primary consumer

(e) Plants and animals

(vi) Tiger

(f) Accumulation of chemicals at successive trophic level

(vii) Tertiary consumer

(g) Skin cancer

(viii) Biomagnification

(h) Ozone-layer depletion

7. Tertiary consumers form the fourth trophic level. 8. Solar energy is converted into chemical energy by heterotrophs. 9. Food chains generally consist of three or four steps. 10. CFCs are used as refrigerants and in fire extinguishers. 11. Aquarium cannot be treated as an ecosystem. 12. All green producers.

plants

and

blue-green

algae

are

(ix) Exposure to UV-rays

(i) Natural aquatic ecosystem

(x) Chlorofluorocarbon

(j) Artificial ecosystem

(xi) Physical environment (k) Grasshopper (xii) Lake

13. Sewage may be used to produce biogas.

(l) Bacteria and fungi

• ANSWERS • A. 1. (a) Abiotic component (b) Ecosystem (c) Omnivores (d) Trophic level (e) Biomagnification (f) Carnivores

12. To freeze the production of chlorofluorocarbon at the 1986 level D. Down: 1. Plastic

2. Because herbivores eat only plants,i.e.,producers

3. Decomposer 5. Consumer

Across: 1. Producer 2. Ozone

3. Rabbits are herbivores, tigers are carnivores and human beings are omnivores

F. I.

4. Microorganisms act as decomposers in an ecosystem. 5. Because autotrophs have chlorophyll that absorb solar energy

II.

6. Because many animals eat more than one kind of food 7. Plants absorb chemicals along with nutrients from soil.

4. Energy

1. (c) 2. (d) 3. (a), (b) 4. (a), (c), (d) 5. (c) 6. (b) 7. (d) 8. (b) 9. (b), (c), (d) 10. (d) 11. (d) 12. (c) 13. (c) 14. (d) 15. (b) 16. (b) 17. (a) 18. (c) 19. (b) 20. (a), (b), (c) 21. (b), (c), (d) 22. (c) 1. biodegradable 2. crop fields 3. Autotrophs 4. chemical energy 5. unidirectional 6. top 7. oxygen 8. interdependent 9. loss 10. environment 11. trophic level 12. food web 13. carnivore 14. top carnivore 15. soil, atmosphere 16. Biodegradable 17. sun 18. chlorophyll

8. Human beings occupy the top position in any food chain.

III.

9. Ozone absorbs ultraviolet rays from sunlight, protecting us from its harmful effects.

1. Yes 2. Yes 3. No 4. Yes 5. Yes 6. No 7. No 8. Yes 9. No 10. Yes 11. Yes 12. No

IV.

1. F 2. T 3. T 4. T 5. F 6. T 7. T 9. T 10. T 11. F 12. T 13. T

10. Chlorofluorocarbon 11. In air-conditioners, refrigerators, aerosol sprays, fire extinguishers

V.

v

8. F

1. (i)(e) (ii)(j) (iii)(a) (iv)(l) (v)(k) (vi)(c) (vii)(d) (viii)(f) (ix)(g) (x)(h) (xi)(b) (xii)(i)

Foundation Sci Bio Class 10 page 166

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Foundation Science: Biology for Class 10

Additional Questions (a) What determines the sex of a child?

1. During a football match, Ankit fell on the ground and shrieked in pain as he had cramps in his right leg. His friend Ojas started massaging Ankit’s calf muscles. After a while Ankit felt better and was able to move without support. (a) What was the cause of Ankit’s muscle pain? (b) Name the process which was responsible for this pain. (c) Do you think Ojas was helpful? Why? 2. Rishav had been feeling tired and weak for the past few weeks. His teacher noticed this and advised his parents to take Rishav to a doctor. The doctor asked Rishav to get a few blood tests done. She advised him to include apples, pomegranates and milk in his diet. She also prescribed iron tablets for him. (a) Why was Rishav feeling tired and weak? (b) Why did the doctor advise a blood test? (c) What values did the teacher show? 3. Akash took a short cut through a slum while going to school. He noticed that some of the people living there had goitre. He explained the importance of using iodized salt to them. He also bought a few packets of iodized salt and distributed these among them.

(b) How did Hitesh show his ignorance? (c) What values did Ramesh show? 7. Harshita found that for every 100 males, there were only 65 females in her village, as many couples aborted female foetuses. Despite opposition from the villagers, she decided to speak out against this practice at the village panchayat. She even got her teacher to explain the importance of a healthy sex ratio to the villagers. (a) What was the sex ratio in Harshita’s village? (b) What was the cause of the poor sex ratio in her village? (c) What qualities did Harshita show? 8. Shankar was happy to notice that the municipal corporation of his city had installed separate garbage bins for biodegradable and nonbiodegradable waste. He explained the importance of the separate garbage bins to his family. He showed them the leaflets that the municipal corporation had distributed. (a) Why was Shankar happy at the installation of separate garbage bins?

(a) Why was goitre common in the slum? (b) Why should we take iodized salt? (c) What values did Akash show? 4. Rajesh’s diabetic grandmother had decided to fast on Ashtami. When she suddenly began to feel weak and dizzy in the afternoon, Rajesh mixed some glucose in a glass of water and made her drink it. She recovered in a few minutes. (a) Why did Rajesh’s grandmother feel weak and dizzy? (b) Why did Rajesh give her the glucose solution? (c) What values did Rajesh show? 5. Prakash’s friend Dheeraj was diagnosed with AIDS. Though his neighbours refused to help Dheeraj, Prakash helped him with his household chores and took him to the hospital regularly. He also explained to the neighbours that they would not contract AIDS if they interacted with Dheeraj. (a) How could Dheeraj have contracted AIDS? (b) It is safe to interact with a person diagnosed with AIDS. Explain. (c) What qualities did Prakash show? 6. Hitesh had three daughters but no sons. He often blamed his wife, Reena, for not giving him a male heir. Ramesh once overheard Hitesh insulting Reena. He visited Hitesh and explained that it is the chromosome of the father in the zygote that determines the sex of the child. The mother plays no role in this respect.

(b) Why do you think the municipal corporation had distributed leaflets? (c) What qualities did Shankar show? 9. The students of Bhagalpur High School organized a street play on how polythene bags harm the environment. They distributed paper and jute bags among the audience. They urged the audience to stop using polythene bags for carrying vegetables, groceries, etc. (a) In what way are polythene bags harmful? (b) Why do people normally carry polythene bags? (c) What qualities did the students of Bhagalpur High School show? 10. Somesh had returned to his village after a few years. He was surprised to notice that the mango grove had given way to a huge factory. The chimneys were emitting black smoke and fly ash. The village pond was being polluted by the effluents from the factory. Trees had been felled to construct houses. People were falling ill more often. Somesh decided to talk to the panchayat about the harmful effects of the degradation of the environment. (a) How was the factory harming the environment of the village? (b) Why do you think the villagers were falling ill more often? (c) Would you say Somesh was sensitive towards the environment? Why?

v