AceGamsat - The Biology Bible

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The Biology Bible Everything you need to know for GAMSAT Biology www.AceGAMSAT.com The information contained in this guide is for informational purposes only. The publication of such Third Party Materials does not constitute a guarantee of any information, instruction, opinion, products or services contained within the Third Party Material. Publication of such Third Party Material is simply a recommendation and an expression of our own opinion of that material. No part of this publication shall be reproduced, transmitted, or sold in whole or in part in any form, without the prior written consent of the author. All trademarks and registered trademarks appearing in this guide are the property of their respective owners. Users of this guide are advised to do their own due diligence when it comes to making decisions and all information, products, services that have been provided should be independently verified by your own qualified professionals. By utilising this guide, you agree that the company AceGAMSAT is not responsible for the success or failure relating to any information presented in this guide. ©2018 AceGAMSAT. All Rights Reserved. AceGAMSAT is not affiliated with ACER in any way.

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About GAMSAT The GAMSAT (Graduate Australia Medical School Admissions Test) has been developed by the Australian Council for Educational Research (ACER). This test selects for students that have the greatest capacity to advance their studies in medicine, dentistry, and pharmacy. The GAMSAT was developed for Australian universities and its component of use for admissions has spread to institutions in the UK and Ireland.

GAMSAT evaluates the nature and extent of abilities and skills gained through prior experience and learning, including the mastery and use of concepts in basic science as well as the acquisition of more general skills in problem solving, critical thinking and writing. Candidates whose first degree is in a non-scientific field of study can still sit GAMSAT and succeed in an application for admission to one of the graduate-entry programs. A science degree is not always a prerequisite and institutions encourage applications from candidates who have achieved academic excellence in the humanities and social sciences. However, it must be stressed that success in GAMSAT is unlikely without knowledge and ability in the biological and physical sciences.

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Table of Contents MACROMOLECULES CARBOHYDRATES NUCLEIC ACIDS PROTEINS LIPIDS

THE CELL CELL THEORY CELL SIZE VISUALISATION OF CELLS CELL STRUCTURE PROKARYOTES EUKARYOTES ENDOMEMBRANE SYSTEM MITOCHONDRIA AND CHLOROPLASTS CYTOSKELETON CELL MOVEMENT FUNGI VIRUS

THE CELL MEMBRANE STRUCTURE PHOSPHOLIPIDS PASSIVE TRANSPORT ACTIVE TRANSPORT ENDOCYTOSIS AND EXOCYTOSIS

ENERGY, METABOLISM, AND RESPIRATION ADENOSINE TRIPHOSPHATE (ATP) CELLULAR METABOLISM GLYCOLYSIS AEROBIC RESPIRATION KREBS CYCLE ELECTRON TRANSPORT CHAIN ENZYMES

1 1 3 8 10

12 12 12 13 14 16 17 19 20 21 22 22 23

24 24 25 26 27 28

30 30 30 32 34 35 36 37

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MITOSIS AND THE CELL CYCLE BINARY FISSION EUKARYOTIC CELL CYCLE INTERPHASE M PHASE

SEXUAL REPRODUCTION AND MEIOSIS STAGES OF MEIOSIS MEIOSIS VS MITOSIS

GENETICS OVERVIEW MENDEL'S FIRST LAW: THE LAW OF SEGREGATION INCOMPLETE DOMINANCE CODOMINANCE PUNNETT SQUARES MENDEL'S SECOND LAW: THE LAW OF INDEPENDENT ASSORTMENT MALE VS FEMALE CHROMOSOMES

THE NERVOUS SYSTEM RESTING POTENTIAL ACTION POTENTIAL THE SYNAPSE TYPES OF NEURONS DIVISIONS OF THE NERVOUS SYSTEM THE EYE THE EAR THE NOSE AND MOUTH

43 43 44 45 45

48 49 51

53 53 55 56 57 57 59 59

62 64 65 66 67 68 72 74 75

THE ENDOCRINE SYSTEM

76

CHEMISTRY OF HORMONES HORMONES IN DETAIL

77 80

REPRODUCTION MALE REPRODUCTIVE SYSTEM FEMALE REPRODUCTIVE SYSTEM

83 83 85

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THE DIGESTIVE AND EXCRETORY SYSTEM MOUTH AND OESOPHAGUS THE STOMACH THE SMALL INTESTINE THE PANCREAS THE LIVER AND GALL BLADDER THE LARGE INTESTINE ABSORPTION THE KIDNEY

THE CARDIOVASCULAR SYSTEM ANATOMY OF THE CARDIOVASCULAR SYSTEM BLOOD VESSELS THE BLOOD

87 88 88 89 91 92 94 94 95

99 99 102 103

THE RESPIRATORY SYSTEM

106

THE LYMPHATIC SYSTEM

109

THE IMMUNE SYSTEM

111

THE MUSCULOSKELETAL SYSTEM

113

SKELETAL MUSCLE CARDIAC MUSCLE SMOOTH MUSCLE

113 114 114

BONES

115

CARTILAGE

118

JOINTS

119

INTEGUMENTARY SYSTEM

120

HOMEOSTASIS

122

APPENDIX

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The Biology Bible

Macromolecules The four classes of biological molecules include carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates The term carbohydrates refer to both saccharides (sugars) and their polymers. Carbohydrates are molecular compounds that are made from just 3 elements – carbon, hydrogen, and oxygen. Students should be aware of the following terms for the GAMSAT: Monosaccharides are the simplest carbohydrates and are also known as single sugars. Glucose is a common monosaccharide and is a major nutrient for cells.

Glucose

Fig. 1 - Different representations of glucose – Fischer (left) and Haworth (right).

Cells extract the energy stored in the glucose molecule by a process known as cellular respiration. Disaccharides are double sugars that consist of two monosaccharides. Maltose is a disaccharide formed by the linking of two molecules of glucose.

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Chemical structures of main sugars

Fig. 2 - Common sugars in biology.

Oligosaccharides are carbohydrates containing a small number of monosaccharides (usually from 3 – 10 monosaccharides).

Polysaccharides can be storage polysaccharides or structural polysaccharides. Examples of important polysaccharides in nature include starch, cellulose, and chitin. Starch is a storage polysaccharide of plants, which is stored as granules in chloroplasts. Starch represents stored energy and can later be withdrawn via hydrolysis to provide the plant with energy. The comparable molecule to starch in animals is glycogen. Animals store glucose as glycogen in the liver and muscle cells. Starch is a polymer of alpha-glucose.

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Highly branched glycogen molecule

Branching occurs here Glucose monomer

Fig. 3 - The structure of glycogen.

Cellulose is a common structural polysaccharide. Cellulose is a polymer of beta-glucose and is found in plant cell walls. Chitin is the structural molecule found in fungi and arthropods. It forms a tough, resistant material.

Nucleic Acids

Nucleic acids carry information inside cells and are responsible for the production of a large number of proteins. They are long polymers of repeating subunits called nucleotides. Each nucleotide consists of a pentose sugar, phosphate group, and an organic nitrogenous base.

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Nucleotide Base Phosphate Sugar

Fig. 4 - Components of a nucleotide.

There are two types of nitrogenous bases that occur in nucleotides:

Nitrogenous bases of DNA and RNA

Fig. 5 - Bases of DNA and RNA.

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Purines: Double-bonded rings found in DNA and RNA. The purines include adenine (A) and guanine (G).

Pyrimidines: Single-ring structure. The pyrimidine found in both DNA and RNA is cytosine (C). The pyrimidine that is found only in DNA is thymine (T), whereas uracil (U) is found only in RNA. In a nucleic acid, the nucleotides are linked to each other via phosphodiester bonds. These bonds are formed between the phosphate of one nucleotide and the sugar of the next nucleotide.

Fig. 6 - Phosphodiester bonds in nucleic acids.

Deoxyribonucleic acid (DNA) DNA is found in the nuclear region of cells and contains the genetic information to create an organism. DNA is arranged as a double helix structure. DNA consists of two polynucleotide chains wrapped around each other along a single helical axis. The spiral shape formed by DNA is termed a double helix. The base pairs on each polynucleotide chain run in opposite directions or antiparallel to each other and are joined by hydrogen bonds between the nitrogenous bases.

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The bases that participate in base-pairing are termed complementary bases. Adenine can pair with thymine in DNA and with uracil in RNA. Cytosine can only pair with guanine.

Ribonucleic acid (RNA)

RNA is identical to DNA but differs in 3 main ways: 1. RNA is single stranded. 2. Carbon number 2 (C2’) on the pentose of RNA is oxygenated.

3. RNA contains uracil instead of thymine.

Fig. 7 - DNA and RNA structure. www.acegamsat.com

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There are three types of RNA:

RIBOSOME

Fig. 8 - The interaction of mRNA with ribosomes.

mRNA: Messenger RNA delivers the DNA code for amino acids to the cytosol to prepare for the manufacturing of proteins.

rRNA: Ribosomal RNA forms ribosomes by combining with proteins. The ribosomes are responsible for directing the synthesis of proteins.

tRNA: Transfer RNA collects amino acids in the cytosol and transfers them to the ribosomes. At the ribosomes, the tRNA is incorporated into the proteins. Remember: RNA is manufactured from a DNA template.

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Fig. 9 - DNA transcription and translation.

DNA (double-stranded) can be transcribed into RNA (single-stranded). DNA stores hereditary information, and the RNA uses this information to create proteins via the sequencing of specific amino acids (translation).

Video: Introduction to DNA Video: RNA Transcription and Translation

Proteins

For the GAMSAT, students should know that proteins have many different functions in cells—enzyme catalysis, transport, defence, structural support, movement, regulation of genes, and storage of ions. Proteins are polymers of amino acids. Any of the 20 amino acids can join together and form long polypeptide chains, which eventually form proteins. Proteins fold into different shapes based on their amino acid composition.

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Cells contain chaperone proteins, which help other proteins fold correctly. Knowledge of chaperones has previously been examined in the GAMSAT, so remember that they assist in the folding of proteins.

TEMPERATURE

If a protein’s environment is altered, the protein may change shape or completely unfold. This is known as denaturation.

Protein Denaturation Fig. 10 - Denaturation of protein with increased temperature.

Proteins can become denatured as a result of changes in pH, ion concentration, and temperature. Denatured proteins are inactive and therefore cannot catalyse reactions. The central dogma of gene expression is that DNA is transcribed into RNA, which is translated to amino acids. Many amino acids link up and form a protein.

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Lipids All lipids are insoluble in water and have a high proportion of non-polar C-H bonds. Saturated lipids occur when all the internal carbon atoms in a fatty acid chain are bonded to at least two hydrogen atoms. Unsaturated lipids occur when a fatty acid has double (or triple) bonds between their internal carbon atoms.

Fig. 11 - Saturated and unsaturated fatty acids.

If a fatty acid has more than one double bond, it is termed polyunsaturated. Most fats contain more than 40 carbon atoms. The fats produced by animals are mostly saturated, whereas plants mostly produce unsaturated fats. Phospholipids are complex lipid molecules and are important as they form the core of all cell membranes in organisms. A phospholipid can be thought of as a triglyceride with a phosphate group replacing one of the fatty acids.

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Fig. 12 - Structure of phospholipids.

The structure of glycerol should be memorized for the GAMSAT. It is a three carbon alcohol, and each carbon atom contains a hydroxyl group. Glycerol forms the backbone of phospholipid molecules.

Fig. 13 - Structure of glycerol.

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The Cell Video: Parts of a Cell Cell Theory The cell theory explains the observation that organisms are composed of cells. This theory includes the following three principles: 1. All organisms are made of one or more cells. Life processes occur in these cells. 2. Cells are the basic units of organization in all organisms. 3. A cell can only arise by division of a previously existing cell.

Cell Size Cells are relatively small for a number of reasons related to diffusion in and out of the cell. A small cell is advantageous in terms of the surface area to volume ratio. A smaller, flatter cell with a large surface area to volume ratio (SA:V ratio) will be more efficient in diffusion and removal of wastes. As a cell gets larger, its volume increases at a faster rate than its surface area (lower SA:V ratio). Surface Area (square inches)

Volume (cubic Inches)

Surface Area / Volume

600

512

500 384

400 300

216 216

200 100

96 24

8

64

3

1.5

1

0.75

0 2

4

6

8

Surface Area (square inches)

2 24

4 96

6 216

8 384

Volume (cubic Inches)

8

64

216

512

Surface Area / Volume

3

1.5

1

0.75

Fig. 14 - Representation of decreasing SA:V as volume increases.

A larger, rounder cell will have less efficient diffusion and removal of wastes. www.acegamsat.com

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Visualisation of Cells Many cells are not visible to the naked eye. In order to visualise the microscopic cells, we need to use microscopy.

Types of microscopes The aim of microscopy is to increase magnification so that cells can appear larger. Types of microscopes used in biology include:

1. Light microscope: - Operate using visible light. - First lens focuses the image onto the second lens. The image is magnified and the image is focused on the back of the eye. - Microscopes that magnify using multiple lenses are called compound microscopes. - Able to resolve structures that are at least 200 nm apart. Because electrons have a much shorter wavelength, an electron microscope (uses electrons instead of visible light) has 1000x the resolving power than a light microscope.

2. Transmission electron microscope: - Electrons transmit through the material. - Resolve images 0.2 nm apart.

3. Scanning electron microscope: - Beams electrons on the surface of the specimen. Electrons reflect back from the surface and other electrons from the specimen are released from the bombardment. - Electrons are amplified and transmitted to a screen. A 3D image is produced. Chemical stains can be used to increase the contrast between different components of the cell. Some structures either absorb or exclude the dye, producing a contrast that aids resolution.

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Cell Structure There are 4 major features that all cells have in common. These include:

1. Nucleoid or nucleus: Genetic material is located here. Every cell contains DNA. Prokaryotes are the simplest organisms and contain a circular molecule of DNA. This DNA is found in the centre of the cell in the region called the nucleoid.

Bacteria Cell Anatomy

Fig. 15 - Important features of bacteria (prokaryote).

Eukaryotes are more complex organisms, and their DNA is found in the nucleus. A double membrane called the nuclear envelope surrounds the nucleus in eukaryotes.

Fig. 16 - 3D structure of the nucleus.

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2. Cytoplasm: The cytoplasm is the semi-fluid matrix that fills the interior of the cell. The cytoplasm contains all of the amino acids, proteins, and sugars that are essential to the cell.

3. Ribosomes: Protein synthesis occurs at the ribosomes.

4. Plasma membrane: The plasma membrane is a phospholipid bilayer with proteins embedded into it. The plasma membrane encloses the cell and separates the internal components of the cell from the environment.

Fig. 17 - Structure of the plasma membrane.

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Types of proteins in plasma membrane: 1. Transport proteins: Help ions and molecules move across the plasma membrane. Movement occurs either in or out of the cell.

2. Receptor proteins: Bring about changes within the cell when the receptors come in contact with molecules such as hormones.

Prokaryotes Prokaryotes are small and are the simplest organisms. They have a plasma membrane that surrounds the cytoplasm. The plasma membrane is surrounded by a rigid cell wall. The rigid cell wall brings strength to the cell.

Fig. 18 - Important features of prokaryotes.

In prokaryotes, the enzymes, DNA, and other cellular constituents are not membrane bound like they are in eukaryotes. Instead, they have access to the entire interior of the cell.

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The two main domains of prokaryotes are bacteria and archaea.

1. Bacteria: -

-

Bacterial cells have a cell wall that consists of peptidoglycan. The cell wall maintains the shape of the cell, protects the cell, and prevents excessive loss or uptake of water. Bacteria can also have an extra protective capsule that surrounds the cell wall. Remember: Bacteria are often susceptible to antibiotics because the antibiotics affect the constitution of the cell wall.

2. Archaea: -

Archaea are difficult to culture and thus have not been studied in detail. Archaea have a cell wall that consists of pseudopeptidoglycan.

Some prokaryotes have rotating flagella that enable movement. Flagella are protein fibres that extend from the cell, and some cells may have one or more flagella.

Eukaryotes Eukaryotic cells are more complex than prokaryotic cells. They contain organelles, which are membrane-bound structures that form compartments. Biochemical processes take place within each compartment.

Fig. 19 - Important features of eukaryotes.

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Eukaryotes have a nucleus that contains DNA. DNA is wrapped into compact units called chromosomes within the nucleus. The nucleus is responsible for the synthesis of nearly all proteins in the living cell. Most eukaryotes have one nucleus, but some fungi may have multiple nuclei. A nucleolus is a region in the nucleus in which synthesis of ribosomal RNA is taking place. The nuclear envelope surrounds the surface of the nucleus in eukaryotes. It has two phospholipid bilayer membranes. The nuclear envelope has pores that allow for the movement of proteins into the nucleus and for the exportation of RNA complexes from the nucleus to the cytoplasm. Chromosomes are composed of chromatin (DNA and protein complex). The DNA is wrapped around histones to form a nucleosome.

Fig. 20 - The composition of chromosomes.

Ribosomes are the cell’s protein synthesis machinery. Ribosomes translate mRNA to produce polypeptides. Polypeptides form proteins. Eukaryotic cells have an internal protein scaffold called the cytoskeleton.

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Students should remember that fungi and plants have cell walls, while animals do not have cell walls.

Endomembrane System The interior of a cell contains an endomembrane system. The role of this system is to allow for the channelling of molecules through the interior of the cell and to provide surfaces for the synthesis of some proteins and lipids.

Fig. 21 - Overview of the endomembrane system.

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This system contains rough and smooth endoplasmic reticulum (ER). The rough ER is the site of protein synthesis. It is studded with ribosomes and synthesises and modifies proteins. The smooth ER lacks ribosomes but still has multiple roles in lipid and carbohydrate synthesis. The Golgi apparatus functions to sort and package proteins. It receives transport vesicles from the ER and then modifies, repackages, and transports them as secretory vesicles. Lysosomes are also components of the endomembrane system in eukaryotes. They contain digestive enzymes that break down molecules and recycle the components of old organelles.

Mitochondria and Chloroplasts Mitochondria and chloroplasts contain their own DNA and have a double membrane structure. The function of mitochondria is to metabolize sugar to generate ATP. The mitochondria have a highly folded inner membrane that contains proteins. These inner membrane proteins, along with the surface proteins, carry out metabolism to produce ATP.

MITOCHONDRIA

Fig. 22 - Production of ATP via photosynthesis.

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Chloroplasts utilize light to generate ATP and sugars. The chloroplasts work by capturing light energy via thylakoid membranes arranged in stacks called grana. The light is essential in the process of forming sugars (glucose). The sugars are broken down by the body and form intermediates that are responsible for the production of ATP in the mitochondria.

Fig. 23 - Chloroplast anatomy.

Cytoskeleton The function of the cytoskeleton is to anchor the organelles and support the shape of the cell. It consists of crisscrossed protein fibres. The cytoskeleton can also help move materials within the cell. The cytoskeleton is composed of different types of filaments and microtubules.

Fig. 24 - The cytoskeleton in eukaryotes.

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Cell Movement Flagella and cilia aid in the movement of the cell. Flagella arise from a basal body while cilia are shorter and more numerous than flagella. Flagella move with a propeller-like motion and cilia move with a back and forth beating motion.

Fig. 25 - Motion of cilia and flagella.

Fungi Fungi are eukaryotic organisms. They can be unicellular (yeast) or multicellular (filamentous fungi like mould or mushrooms). Fungi can reproduce both sexually and asexually. Hyphae are long-branching, filamentous structures of fungi. Hyphae are collectively termed mycelium.

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Fig. 26 - Filamentous fungi (mushroom).

Viruses Viruses are very small, obligate, intracellular parasites. Viruses are considered nonliving as they have no cellular structure and cannot carry out their metabolism independently. This means that in order to replicate their genetic material and thus multiply, they must be inside a living cell. The following figure shows the steps involved in the replication of DNA within a host cell.

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Fig. 27 - Attachment and replication of DNA in a host cell.

1. Attachment - Virus attaches to cell surface 2. Entry and degradation – Viral DNA is injected into the cell; the coat of the

3. 4. 5. 6.

virus remains outside and is degraded Replication – Nucleic acid is replicated in host cell Synthesis – New protein coats are synthesised within the host cell Assembly – Mature virions are assembled within the cell Release – Cell ruptures, releasing mature virus particles

Viruses may have DNA or RNA as their genetic material, but they cannot have both. The genetic material of a virus is found in their protein coat, which is termed the capsid.

Fig. 28 – Bacteriophage, a virus that infects and replicates within a bacterium.

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The Cell Membrane Video: Cell Membrane Introduction Video: Transport across the Cell Membrane Video: Endocytosis and Exocytosis The cell membrane or plasma membrane encases all living cells in a bilayer formed by phospholipids.

Structure The fluid mosaic model describes the membrane as being fluid-like with a mosaic of proteins floating inside.

Fig. 29 - Components of the cell membrane/plasma membrane.

The cell membrane consists of four component groups.

1. Phospholipid bilayer: Every cell membrane has a phospholipid bilayer. Many components of the membrane are embedded in this bilayer.

2. Membrane proteins: This collection of proteins floats in the lipid bilayer. Integral proteins are embedded in the membrane, and peripheral proteins are associated with the surface of the membrane.

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3. Interior protein network: Intracellular proteins provide structural support to the membrane.

4. Cell-surface markers: The membrane has glycoproteins and glycolipids, which act as cell identity markers.

Phospholipids Phospholipids spontaneously form bilayers. They are composed of two fatty acids and a phosphate group linked to a 3-carbon glycerol molecule.

Fig. 30 - Structure of phospholipids.

The phosphate group of the phospholipid is hydrophilic (water-loving). The fatty acids are hydrophobic (water-hating) and non-polar. The fluidity of the membrane depends on the composition of fatty acids in the membrane. Unsaturated fatty acids make the membrane more fluid, but saturated fatty acids make the membrane less fluid-like. Temperature also affects the fluidity of the membrane with an increase in temperature causing an increase in fluidity.

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Passive Transport Transport across the membrane can occur via diffusion, which is a type of passive transport. No energy is required for passive diffusion as it involves moving a substance along a chemical or electrical gradient.

Fig. 31 - Simple diffusion through a plasma membrane.

The cell membrane creates a barrier for hydrophilic polar molecules, while it allows for hydrophobic substances to diffuse through. Ions and large hydrophilic molecules cannot directly pass through the phospholipid bilayer. However, these molecules can still pass through with the help of proteins (carrier proteins and protein channels). This process is known as facilitated diffusion. The proteins can either be carriers or channels. Channels allow for the diffusion of ions through a protein channel while carriers bind to the molecules they transport. The process of water moving across the membrane is termed osmosis. The following figure shows water moving through a selectively permeable membrane by osmosis. Water is moving to a high concentration of solutes or a low concentration of water.

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Fig. 32 - Osmosis of water through a selectively permeable membrane.

Water will move to an area with a higher concentration of solutes or an area with a lower concentration of water.

Active Transport Active transport involves the use of energy to move substances against a concentration gradient. Specialised protein carriers are used along with a source of energy to transport substances. There are different types of transporters: 1. Uniporters – transport a specific molecule in one direction. 2. Symporters – transport two molecules in the same direction. 3. Antiporters – transport two molecules in opposite directions.

Fig. 33 - Different types of transporters used for active transport.

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The cell membrane contains a sodium-potassium pump. This pump uses ATP and moves sodium out of the cell and potassium into the cell against their concentration gradients. Three sodium atoms are pumped out for every two potassium atoms that enter the cell.

Fig. 34 - The sodium-potassium pump in action.

Endocytosis and Exocytosis Large quantities of substances cannot pass through the membrane by diffusion. Large quantities of substances must enter the cell via endocytosis, which involves the cell membrane surrounding the material and pinching off to form a vesicle.

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Fig. 35 - Formation of a vesicle during endocytosis.

Large quantities of material can leave via exocytosis. This involves the material being released from the cell when the vesicle fuses with the membrane.

Fig. 36 - Vesicle joining with membrane during exocytosis.

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Energy, Metabolism, and Respiration Video: Glycolysis Video: Krebs / Citric Acid Cycle Video: Electron Transport Chain Video: Enzyme-Induced Fit Model

Adenosine Triphosphate (ATP) ATP is the source of energy used in cellular energy transactions. ATP consists of three phosphate groups, ribose, and adenine.

Fig. 37 - The three components of ATP.

The chemical bonds in ATP are important for the storage and release of energy. An enzyme (protein kinase) removes a phosphate group from ATP and energy is released. This energy is used in cellular reactions.

Cellular Metabolism Metabolism is the total of all chemical reactions carried out by an organism. There are two types of reactions – catabolism and metabolism. www.acegamsat.com

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Fig. 38 - Features of anabolic and catabolic reactions.

1. Catabolism: Reactions that produce energy by breaking down molecules.

2. Anabolism: Reactions that use energy to build up molecules. There are 3 basic stages of metabolism. These include: a. Macromolecules are broken down into their constituent parts. For example, proteins, lipids, and polysaccharides are broken down into amino acids, fatty acids, and monosaccharides, respectively. b. These constituent parts are oxidized to produce acetyl-CoA, pyruvate, and other metabolites. Some ATP is formed during this process along with NADH and FADH2. This process does not directly use oxygen. c. If oxygen is present and the cell can utilize this oxygen, the metabolites formed (stage 2) can go into the citric acid cycle, and oxidative phosphorylation will take place to form large amounts of energy (ATP, NADH, or FADH2).

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Stages 1 and 2 both produce energy. These stages are called respiration. If no oxygen is used, the respiration is anaerobic. If oxygen is used, the respiration is aerobic.

Fig. 39 - Stages and processes of metabolism.

Glycolysis Glycolysis is the first stage of anaerobic and aerobic respiration. Glycolysis involves breaking down a 6-carbon glucose molecule into two 3-carbon pyruvate molecules. Glycolysis will occur in the presence or absence of oxygen. The reactions of glycolysis occur in the cytosol of the cell.

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The steps of glycolysis can be seen in the figure below:

Fig. 40 - Steps involved in glycolysis.

Overall, two ATPs are used and four ATPs are produced. Two pyruvate molecules and two NADH molecules remain at the end of glycolysis. Glycolysis is best learned visually (see video: Glycolysis) so students can see the process occurring in the cell.

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Aerobic Respiration

If oxygen is present in a cell that can undergo aerobic respiration, the products of glycolysis (NADH and pyruvate) will move into the matrix of a mitochondrion.

Fig. 41 - The NADH and pyruvate will diffuse (facilitated diffusion) through the outer membrane.

The pyruvate diffuses into the matrix and is converted to acetyl-CoA in a reaction that also produces CO2 and NADH.

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Krebs Cycle (Citric Acid Cycle) Amino acids can be deaminated and converted to pyruvic acid or acetyl-CoA. Fatty acids can be converted to acetyl-CoA. Acetyl-CoA is responsible for the initiation of the Krebs cycle.

Fig. 42 - The fuel for the citric acid cycle – acetyl-CoA.

Acetyl-CoA is a coenzyme, which transfers two carbons from pyruvate to oxaloacetic acid, that initiate the Krebs cycle. Each turn of the Krebs cycle produces one ATP, three NADH, and one FADH2. During each cycle, two carbon atoms are lost as CO2. The process of producing ATP in the Krebs cycle (citric acid cycle) is termed substratelevel phosphorylation. Detailed knowledge of each step of the Krebs cycle is not required for the GAMSAT.

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Electron Transport Chain The electron transport chain (ETC) is a series of proteins in the inner membrane of the mitochondrion. Electrons from NADH and FADH2 are passed through the series of proteins and are accepted by oxygen to form water.

Fig. 43 - Electrons passing through a series of proteins in the ETC.

As these electrons are passed through the protein series, protons are pumped into the intermembrane space. This creates a proton gradient, which is termed the proton-motive force. In the above figure, notice that the proton-motive force moves protons back into the mitochondrial membrane through ATP synthase to produce ATP. 2-3 ATP molecules are produced from each NADH and 2 ATP molecules are produced from each FADH2.

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1. The overall products and reactants for aerobic respiration are: C6H12O6 + 6O2  6CO2 + 6H2O Glucose and oxygen react to form carbon dioxide, water, and energy. 2. The overall products and reactants for anaerobic respiration are: C6H12O6  2C2H5OH + 2CO2 Glucose reacts to form ethanol and carbon dioxide in the absence or when there is a lack of oxygen. 3. The overall products and reactants for photosynthesis are: 6CO2 + 6H2O  C6H12O6 + 6O2 Carbon dioxide and water react in the presence of light (energy) to form glucose and oxygen.

Enzymes Enzymes are biological catalysts that lower the activation energy of a reaction. A lower activation energy results in the reaction proceeding more quickly than without an enzyme present.

Fig. 44 - Differences in activation energy in the presence and absence of an enzyme.

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The enzyme itself is not changed or consumed in the reaction, so only a small amount of enzyme is needed and can be recycled. Enzymes contain active sites that conform to fit the shape of substrates. This allows for the substrate to bind to the active site of the enzyme. Most enzymes are proteins.

Fig. 45 - The conformation of enzyme active sites to fit the shape of substrates.

Enzyme function can be affected by environmental factors. The rate of an enzymecatalysed reaction is affected by the concentration of the reaction substrate and enzymes. In the presence of excess substrate, an increase in the concentration of enzyme will increase the reaction rate in a linear fashion. In the presence of a constant enzyme concentration, an increase in substrate concentration will increase the reaction rate until it reaches the maximum rate. This maximum rate is reached when all the active sites of the enzymes are saturated with substrate. This is demonstrated in the figure below, with Vmax being the maximum rate at which the reaction can take place (with constant enzyme concentration).

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Fig. 46 - Limiting rate of reaction with constant enzyme concentration.

Chemical and physical factors can alter the shape of the enzyme, which then affects the ability of the enzyme to catalyse the reaction. These factors include temperature, pH, and the presence of regulatory molecules.

Temperature The rate of an enzyme catalysed reaction increases with increasing temperature, but only until it reaches a certain temperature called the optimum temperature.

Fig 47 - Rate of reaction at a range of temperatures.

At temperatures above the optimum temperature, the enzyme will denature and lose functionality.

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The optimum temperature of an enzyme usually corresponds to the temperature in which it is found in the body.

pH Most enzymes have an optimum pH that ranges from a pH of 6-8 such as trypsin, which is an enzyme found in the small intestine. Some enzymes have an optimal pH at 2 such as pepsin, which is found in the stomach.

Fig. 48 - Optimal pH for three different enzymes.

Enzymes that are not at their optimal pH will function with decreased efficiency and may even become denatured.

Inhibitors and activators Different substances can bind to enzymes and alter their shape. An inhibitor is a substance that can bind to an enzyme and decrease its activity. There are two types of enzyme inhibition – competitive and non-competitive inhibition.

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Fig. 49 - Competitive and non-competitive inhibition.

1. Competitive inhibition: Inhibitors compete with the substrate for the same active site on the enzyme. 2. Non-competitive inhibition: Inhibitors bind to a location other than the active site. This changes the shape of the enzyme and it will not be able to bind to the substrate. An allosteric activator binds to allosteric sites in the enzyme. This keeps the enzyme in its active configuration and increases the activity of the enzyme. An allosteric inhibitor binds to the allosteric sites in the enzyme and decreases the enzyme’s activity.

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Fig. 50 - Characteristics of allosteric inhibition and activation.

Enzyme cofactors Cofactors are inorganic chemical components that assist in the functioning of enzymes. Cofactors are usually metals such as Zn2+ or Cu2+. Coenzymes are organic molecules that are required for the functioning of certain enzymes. They bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction. Many enzymes need a cofactor (vitamin or mineral) to activate them. Without the cofactor, the enzyme cannot lock the substrate into its active site, so the reaction will not take place.

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Mitosis and the Cell Cycle Video: Interphase Video: Mitosis Video: Bacterial Binary Fission Binary Fission Bacteria divide by a process known as binary fission.

Fig. 51 - The process of binary fission in bacteria.

The process involves the migration of two identical DNA molecules to opposite ends of the cell. The cell then divides in two and each new cell enlarges to the original size. DNA replication proceeds bidirectionally from the origin to a specific termination site.

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The doubling time of bacteria in the presence of unlimited resources can be calculated as follows:

b = B x 2n b is the number of bacteria at the end of the time interval. B is the number of bacteria at the beginning of the time interval. n is the number of generations. Example: A bacteria culture initially contains 1000 bacteria. Find the number of bacteria after 5 generations. Given: B = 1000, n = 5, b = ? Formula: b = B x 2n Solution: b = 1000 x 25 b = 1000 x 32 b = 32,000 So, there will be 32,000 bacteria left after 10 generations.

Eukaryotic Cell Cycle The eukaryotic cell cycle is divided into 5 different phases.     

Gap 1 (G1) Synthesis (S) Gap 2 (G2) Mitosis Cytokinesis (C)

G1, S, and G2 are collectively called interphase. Mitosis and cytokinesis are collectively called M phase.

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The following image shows the different phases of the eukaryotic cell cycle:

Fig. 52 - The different phases of the eukaryotic cell cycle.

Interphase Interphase takes place for the preparation of mitosis. G1, S, and G2 are subphases of interphase. G1 is the primary growth phase. DNA synthesis occurs in the S phase. The G 2 phase occurs before mitosis and after the S phase.

M Phase The M phase contains mitosis and cytokinesis and occurs after the G2 phase. Mitosis can be divided into 5 stages – prophase, prometaphase (note: some resources do not include this as a major phase), metaphase, anaphase, telophase. Cytokinesis then occurs.

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MITOSIS

Fig. 53 - The M phase of the cell cycle, consisting of mitosis and cytokinesis.

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The DNA has been replicated after G2 phase.

Prophase: chromosomes condense and become visible. Chromosomes are seen as two sister chromatids and are held together by a centromere. Spindles begin to form.

Prometaphase: chromosomes attach to microtubules and chromosomes move to the equator of the cell.

Metaphase: chromosomes are aligned along the centre of the cell in a straight line. The equator of the cell is called the metaphase plate.

Anaphase: centromeres of sister chromatids are degraded and individual chromosomes are freed. Chromosomes move to opposite poles and spindle poles move apart.

Telophase: the clustered chromosomes at each pole decondense. Nuclear envelopes form around the chromosomes.

Cytokinesis divides the cell into two separate cells. The cell cycle can be halted at 3 different checkpoints. The checkpoints include: 1. G1/S - commitment to divide. 2. G2/M - important to ensure the integrity of DNA. 3. Spindle assembly checkpoint – ensures all chromosomes are attached to the spindle fibres (during M phase).

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Sexual Reproduction and Meiosis Video: Comparing Mitosis and Meiosis Video: Chromosomal Crossover in Meiosis I Video: Phases of Meiosis I Video: Phases of Meiosis II

Sexual reproduction involves the genetic contribution of two cells. The process of meiosis reduces the number of chromosomes. Haploid cells (1n) such as sperm and egg cells contain one set of all chromosomes.

Fig. 54 - Two haploid cells (sperm and egg) fuse together to form a diploid zygote.

During fertilisation, two haploid gametes fuse together and form a diploid zygote (2n) containing two sets of chromosomes. Meiosis and fertilisation together form a cycle of reproduction. Somatic cells have two sets of chromosomes and are thus diploid cells. Only one set of chromosomes is present in the haploid gametes (egg or sperm). www.acegamsat.com

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Fig. 55 - Visual representation of haploid versus diploid cells.

Remember: Haploid = 1 set of chromosomes Diploid = 2 sets of chromosomes In animals, the zygote undergoes mitosis, which gives rise to all cells in the body. On the other hand, germline cells undergo meiosis to form egg or sperm cells (haploid gametes). All non-germline cells are called somatic cells.

Stages of Meiosis Meiosis consists of two divisions and mitosis consists of only one division. The two divisions of meiosis are termed meiosis I and meiosis II. Visual learning is the most effective way to study meiosis. The video links for this chapter provide explanations of each step of meiosis I and II to the required depth for the GAMSAT. The Meiosis processes are:

Meiosis I  Prophase I  Metaphase I  Anaphase I  Telophase I

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Fig. 56 - The processes of meiosis I.

Meiosis II  Prophase II  Metaphase II  Anaphase II  Telophase II

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Fig. 57 - The processes of meiosis II.

Meiosis Versus Mitosis For the GAMSAT, students must clearly understand the differences between the process of mitosis and meiosis. Observe the following diagram showing the processes of mitosis and meiosis side-by-side.

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Fig. 58 - Meiosis versus mitosis.

Differences between meiosis and mitosis: - In meiosis, maternal and paternal chromosomes pair and share genetic information with each other via crossing over. This does not occur in mitosis. - The replication of DNA is suppressed between meiosis I and meiosis II. - Meiosis produces cells that are different from each other. This is due to crossing over and the independent assortment of homologous chromosomes. - Meiosis produces haploid cells (n) and mitosis produces diploid cells (2n).

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Genetics Video: Introduction to Heredity Video: Punnett Square Video: Sex-linked Traits Video: Alleles and Genes Overview Genetics is the study of heredity and variations in organisms by dealing with the means by which traits are passed from parents to offspring. Gregor Mendel made some important observations that became the foundation of genetics. Mendel crossed purple flowers with white flowers and found that the F1 generation produced purple flowers. He called this purple trait dominant and the white trait recessive. When he self-pollinated the F1 generation plants, the F2 generation expressed dominant and recessive traits in a 3 to 1 ratio.

Fig. 59 - Mendel’s experimental results represented by Punnett squares.

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Important to remember for the GAMSAT: The phenotype is the expression of a trait. The genotype is the genetic makeup of a trait. When both alleles are dominant, the dominant phenotype is expressed – YY When both alleles are recessive, the recessive phenotype is expressed - yy

If an individual has two recessive or two dominant alleles, it is termed homozygous – yy or YY. If an individual has one recessive and one dominant allele, it is termed heterozygous – Yy.

Fig. 60 - Genotypes and their respective phenotypes.

Complete dominance means for any one trait, a diploid individual will have two chromosomes that code for a specific trait. These two chromosomes are termed homologous chromosomes. The corresponding genes are located at the same positions on the respective chromosomes. Each gene contributes an allele to the genotype and only one allele is expressed (dominant allele). www.acegamsat.com

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Mendel’s First Law: The Law of Segregation Alleles segregate independently of each other when forming gametes. Any gamete is equally likely to possess any allele and the phenotypic expression of alleles is the expression of the dominant allele.

› Fig. 61 - Independent segregations of alleles during gamete formation.

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Incomplete Dominance Incomplete dominance is seen when a heterozygous individual exhibits a phenotype that is intermediate between the homozygous counterparts. For example, a cross between a red and white flower may produce a pink flower.

Fig. 62 - An example of incomplete dominance with flower colour.

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Codominance Codominance occurs when a heterozygote exhibits both phenotypes. For example, a heterozygote for human blood types exhibits A and B antigens on the blood cell membranes.

Fig. 63 - An example of codominance with blood types.

Punnett Squares It is important that students remember how to interpret Punnett squares, as they are examined in most GAMSAT exams. Punnett squares are used when predicting the ratio of different genotypes in offspring. They are formed by placing the gametes from one parent along the top of the square. The gametes from the other parent are placed along the side. The following shows a monohybrid cross between green and yellow peas. A capital letter represents a dominant trait and a lower case letter represents a recessive trait.

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Fig. 64 - Punnett square showing a cross between green and yellow pea seeds.

The genotypes of all possible gametes of each parent are displayed in the first column and row. The alleles are then combined in the respective boxes to show the possible genotypes of the offspring. Each offspring genotype is equally likely (law of segregation). We can see here that yellow peas are dominant over green peas. A cross between a heterozygous yellow pea and a homozygous green pea is shown above. The Punnett square shows that 50% of the peas are green (yy) and 50% are yellow (Yy). A Punnett square can also be used to predict the phenotypical ratio of a dihybrid cross. This is used to study how two different traits will be expressed in the offspring. For example, it can be used to determine the ratio of yellow/green and wrinkled/smooth peas.

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Fig. 65 - Dihybrid cross for yellow/green and wrinkled/smooth pea seeds.

Mendel’s Second Law: The Law of Independent Assortment This law of independent assortment states that genes on different chromosomes will assort independently of each other. For example, genes that control pea colour and pea shape will assort independently of each other when on different chromosomes.

Male Versus Female Chromosomes The twenty-third pair of chromosomes in humans determines the sex of the individual. Each chromosome of the pair is called a sex chromosome. The twentythird pair of chromosomes appear in the karyotype as XX for a female and XY for a male.

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Fig. 66 - Male and female sex chromosomes.

When a gene is found on a sex chromosome, it is called sex-linked. In most cases, the Y chromosome does not carry the allele for the sex-linked trait. As a result, the allele that is carried on the X chromosome of the male is expressed whether it is recessive or dominant. In somatic (non-sexual) cells, one of the X chromosomes will condense and the genes will become inactive and form a Barr body.

The following Punnett square shows a cross between sex-linked traits:

Fig. 67 - Cross between a sex-linked condition – colourblindness. www.acegamsat.com

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The Punnett square shows a cross between a carrier female and normal male for colourblindness. Since there are two possible phenotypes for the males, and one is the recessive phenotype, the male offspring from such a pairing have a 50% chance of being colourblind. It is important to remember that even though genotype determines phenotype, the environment will still influence this relationship. The environment can be both internal and external factors. For example, nutrition, temperature, humidity, and stress can all have an effect on the phenotype. Real life examples: - Human skin colour is influenced by both genetics and environmental conditions. - The coat colour of the arctic fox is influenced by heat sensitive alleles. - The colour of Hydrangea flowers are influenced by soil pH.

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The Nervous System Video: Anatomy of a Neuron Video: Sodium-Potassium Pump Video: Electronic and Action Potential Video: Synapse Structure Video: Chemical Neuronal Synapses Video: Autonomic Nervous System

The nervous system is responsible for communication between specific parts of the body. The nervous system is responsible for changes in muscular contractions and endocrine secretions. It contains the brain, spinal cord, nerves, and sensory organs such as the eye and ear.

Fig. 68 - Pathway of the nervous system throughout the human body.

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The functional unit of the nervous system is the neuron. This highly specialised cell is capable of transmitting an electrical signal from one cell to another. Neurons will have a different appearance depending on where they are found in the body, but all neurons have a basic anatomy. Neurons generally have a cell body, an axon with many branches, and many dendrites.

Fig. 69 - General structure of a neuron.

The dendrites receive a signal to be transmitted. This signal passes through the cell body and an action potential will be produced if the signal is great enough. The action potential will move from the cell body and down the axon.

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Fig. 70 - The synapse is the communication route between neurons.

The axon carries the action potential to a synapse, which passes the signal to the next cell. When an action potential is generated down a myelinated axon, the action potential jumps from one node of Ranvier to the next.

Resting Potential A resting potential occurs across the plasma membrane of all cells. The resting potential outside the cell membrane is positive and the resting potential inside the membrane is negative (-70mv). This is because the membrane contains a Na-K+ ATPase that pumps Na+ to the outside of the cell and K+ to the inside of the cell. More Na+ is pumped outward than K+ inward (3 Na+ per 2 K+). Another reason for the negative internal membrane potential is due to K+ leaking out of the cell. Overall, there is a gain of positive charge on the outside of the membrane and a loss of positive charge from the inside of the membrane. This creates a membrane potential, which is the basis of all conduction of impulses by both muscle and nerve fibres.

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Action Potential The action potential is a disturbance in the electric field across the membrane of a neuron. A stimulus can make the membrane suddenly permeable over and above a threshold potential. This increased membrane permeability will cause the influx of Na+ ions (influx of positive charge). This causes a reversal of membrane potential as the inside of the cell becomes positive and the outside becomes negative. This state is termed depolarisation. After depolarisation, the nerve functions to reach its previous resting potential. During this state, the Na+ channels close and the voltage-gated K+ channels open. This state is known as repolarisation.

Fig. 71 - The firing of a neuron – action potential.

Note: The action potential is all-or-nothing, which means that the membrane either completely depolarises or no action potential is produced. Therefore, for an action potential to be generated, the stimulus must be greater than the threshold stimulus.

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Fig. 72 - Nerve impulse action potential in the neuron.

The Synapse

Neural impulses are transmitted from one cell to another via a synapse. These impulses are transmitted either chemically or electrically. There are three major steps that occur at the synapse. 1. The synaptic vesicles in the terminal buttons of a sending neuron release neurotransmitters into the synaptic space. 2. The neurotransmitters cross the synaptic space to the receiving neuron. 3. After crossing the synaptic space, the neurotransmitters fit into receptor sites located on the dendrites or cell body of the receiving neuron.

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Types of Neurons

There are 3 main types of neurons in the nervous system.

Fig. 73 - Types of neurons.

Interneurons: transfer signals from neuron to neuron. Sensory neurons (afferent): receive signals from a receptor cell that interacts with the environment. The sensory neuron then transfers the signal to other neurons. Motor neurons (efferent): carry signals to a muscle or gland (effector).

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Divisions of the Nervous System The two major divisions of the nervous system are the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is connected to the whole body via the PNS. For the purpose of the GAMSAT, think of the CNS as the brain and spinal cord, and the PNS as all other nerves and ganglion in the body.

Fig. 74 - Divisions of the nervous system.

Peripheral Nervous System: The PNS can be divided into the somatic nervous system (SoNS) and autonomic nervous system (ANS). SoNS carries out sensory and motor functions. Motor neurons innervate skeletal muscle only. The motor function is voluntary as it can be consciously controlled. ANS is involuntary and has a sensory and motor portion. The sensory portion receives signals from the organs in the body and the motor portion conducts these signals to smooth muscle, glands, and cardiac muscle.

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The motor portion of the ANS is further divided into sympathetic and parasympathetic systems. Most internal organs are innervated with the two systems working in opposition to each other. Sympathetic encompasses the fight or flight response. Increase blood flow to muscles (increase heart rate) and reduce blood flow to stomach for digestion (constrict blood vessels).

Fig. 76 - Effects of sympathetic stimulation.

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Parasympathetic deal with rest and digestion. Works in opposition to the sympathetic system. Decreases blood flow to muscle (decrease heart rate) and increases blood flow to stomach for digestion (dilate blood vessels).

Fig. 77 - Effects of parasympathetic stimulation.

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Neurotransmitters: Parasympathetic system - neurotransmitter is acetylcholine. Sympathetic system - neurotransmitter is noradrenaline or adrenaline. Receptors for acetylcholine are called cholinergic receptors, and receptors for noradrenaline and adrenaline are called adrenergic receptors.

Central Nervous System: The CNS contains the spinal cord, the lower brain, and the higher brain. The lower brain consists of the medulla, hypothalamus, thalamus, and cerebellum. It is important for involuntary activities such as respiration, emotions, and pain/pleasure.

Fig. 78 - Anatomy of the brain.

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The higher brain contains the cerebrum and cerebral cortex. It is important for processing thoughts and storing memories.

The Eye For the GAMSAT, students should learn the basic anatomy of the eye and the function of its basic parts.

Fig. 79 - Components of the human eye.

Cornea: the cornea is the outer covering of the eye. The cornea increases the ability of the eye to properly focus on light. Sclera: this is the white layer on the outside of the eye. It provides structure and protection for the inner components of the eye. www.acegamsat.com

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Pupil: the pupil appears as a black area at the front of the eye. This black area is a hole that takes in light, allowing the eye to focus on the objects in front of it. Iris: the iris is the coloured area that surrounds the pupil. It uses the dilator pupillae muscles to dilate or contract the pupil. This allows the eye to take in more or less light, depending on the surrounding light levels. Lens: the lens is situated behind the pupil. The lens focuses the light that comes through the pupil. It is held in place by the ciliary muscles, which change the shape of the lens so that light can effectively be focused onto the retina. Retina: the light focused by the lens will be transmitted onto the retina (back of the eye). The retina contains rods and cones arranged in layers. Cones can distinguish between colours but rods cannot. The retina is connected to the optic nerve. Optic nerve: transmits visual information from the eye to the brain for interpretation. Choroid: the choroid lies between the retina and the sclera and provides blood supply to the eye. Vitreous humour: the vitreous humour is the gel located in the back of the eye and helps maintain the shape of the eye. Aqueous humour: the aqueous humour is a watery substance that fills the front of the eye. Its function is to maintain the shape of the eye.

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The Ear For the GAMSAT, students should be aware of the basic anatomy of the ear and the function of its basic parts. There are three basic parts of the ear – the outer ear, middle ear, and inner ear.

Fig. 80 - Important structures in the outer, middle, and inner ear.

The pinna or auricle is the skin and the cartilaginous flap on the outer part of the ear. The auricle collects sound waves and channels them into the external auditory canal (ear canal). The middle ear begins at the tympanic membrane (ear drum). The middle ear consists of three tiny bones – malleus, incus, and stapes. These bones translate the sound wave to the oval window. www.acegamsat.com

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The sound wave then enters the inner ear and moves into the cochlea. As the wave moves through the cochlea, the alternating rise and fall in pressure move the vestibular membrane in and out. This movement is detected by the hair cells of the organ of Corti and then transformed into neural signals, which are sent to the brain. The inner ear also contains fluid-filled semicircular canals, which are responsible for balance.

The Nose and Mouth The sense of smell is termed olfactory, and the sense of taste is termed gustatory. These senses involve chemoreceptors, which play an important role in sensing different chemicals. There are four primary taste sensations – sour, salty, bitter, and sweet.

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The Endocrine System The endocrine system is the set of tissues, glands, and cells that secrete hormones into the body’s fluids (the blood most often). The function of the endocrine system is to alter metabolism and regulate growth and development.

Fig. 81 - Components of the endocrine system.

The nervous system stimulates many endocrine glands to secrete their hormones. Endocrine hormones are released into the general circulation and act by binding to highly specific receptor proteins.

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Pituitary gland: secretes many different hormones, some of which affect other glands Hypothalamus: region of the brain controlling the pituitary system Parathyroid gland: helps regulate the level of calcium in the blood Thyroid gland: affects metabolism Adrenal glands: helps trigger the fight-or-flight response Pancreas: regulates the level of sugar in the blood Testicle: secretes male sex hormones Ovary: secretes female sex hormones

Chemistry of Hormones For the GAMSAT, students should be familiar with the basic role of hormones. The following three types of hormones are categorized based on their chemistry: - Steroid hormones - Peptide hormones - Tyrosine derivatives Steroid hormones: Steroid hormones are derived from cholesterol. Since they are lipids, they require a protein transport molecule to dissolve in the blood stream. These hormones are lipid soluble and can diffuse through the cell membrane of the target cell.

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Fig. 82 - Action of steroid hormones.

After entering the cell, the steroidal hormones combine with a steroid receptor in the cytoplasm. The receptor then transports the steroid hormone into the nucleus where it interacts to increase protein synthesis. Steroid hormones to learn for the GAMSAT: Glucocorticoids and mineral corticoids - cortisol and aldosterone. Gonadal hormones - estrogen, progesterone, and testosterone. Further details of these hormones will be examined later in the chapter.

Peptide hormones: Peptide hormones are derived from peptides. These can also be termed protein hormones. These hormones are water-soluble and can move freely through the blood but have trouble diffusing through the membrane of the target cell. As a result, they attach to membrane-bound receptors, which carry the hormone through the cell. www.acegamsat.com

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Fig. 83 - The action of the peptide hormone, insulin.

Notice that insulin allows for the uptake of glucose into the cell. Peptide hormones can act directly to alter membrane permeability to ions or may activate secondary messengers (cAMP), which activate or deactivate enzyme and/or ion channels. Peptide hormones to learn for the GAMSAT: Anterior pituitary hormones – FSH, LH, ACTH, hGH, prolactin, and TSH. These hormones are released from the anterior pituitary gland.

Pituitary hormones – oxytocin and ADH. The posterior pituitary gland is controlled by signals from the hypothalamus. Pancreatic hormones – insulin and glucagon. These hormones are released from the pancreas.

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Parathyroid hormone – PTH. This hormone is released from the parathyroid glands. Tyrosine derivatives:

Tyrosine derivatives are hormones formed by enzymes in the rough ER or cytosol, which function to increase metabolism and growth and development. Tyrosine derivatives to learn for the GAMSAT: The first type of tyrosine derivatives are the thyroid hormones – T3 and T4.

Protein carriers must carry thyroid hormones in the blood, as the hormones are lipid soluble. They function to increase the transcription of genes in most cells in the body. The second type of tyrosine derivatives are the catecholamines – epinephrine (adrenaline) and norepinephrine (noradrenaline). The catecholamines can dissolve in blood as they are water-soluble. They can directly bind to receptors in the target tissue and produce their effects by acting through the second messenger, cAMP.

Hormones in Detail It is not entirely necessary to know the role of the following hormones in detail, but it is important to know the general function of each hormone, as this will increase speed, efficiency, and understanding of the exam. Anterior pituitary hormones: Follicle stimulating hormone (FSH) – regulates the function of testes and ovaries. Luteinizing hormone (LH) – triggers ovulation and development of the corpus luteum in females. Adrenocorticotropin (ACTH) – stimulates the adrenal cortex to release glucocorticoids.

Human growth hormone (hGh) – stimulates growth in most cells of the body. Increases protein synthesis and mobilization of fat. Prolactin – promotes milk production of the beasts.

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Thyroid-stimulating hormone (TSH) – stimulates the release of T3 and T4 and increases the size of the thyroid gland. These hormones increase metabolism, growth, and development. Posterior pituitary hormones: Oxytocin – increases uterine contractions during pregnancy.

ADH – causes collecting ducts of the nephron (kidney) to become more permeable to water. This reduces the amount of urine product and increases the concentration of the urine. This also causes an increase in blood pressure. The adrenal cortex secretes two types of hormones: mineral corticoids and glucocorticoids.

Fig. 84 - Different hormones released from the adrenal medulla and adrenal cortex.

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Aldosterone – a mineral corticoid that acts in the distal convoluted tubule and the collecting duct of the nephron. It functions to increase the reabsorption of sodium and chlorine ions, which creates an eventual increase in blood pressure. Cortisol – a glucocorticoid that stimulates gluconeogenesis (breakdown of glycogen) in the liver, which produces an increase in blood glucose levels. The adrenal medulla secretes catecholamines. These include: Epinephrine and norepinephrine – these are vasoconstrictors of most internal organs and skin but are vasodilators of skeletal muscle. These hormones are important for the “fight or flight” response.

Thyroid hormones: T3 and T4 – T3 contains three iodine atoms and T4 contains four iodine atoms. Their function is to increase the basal metabolic rate.

Calcitonin – decreases blood calcium by decreasing osteoclast number and activity. Pancreatic hormones: Insulin – lowers blood glucose levels. Insulin stores carbohydrates as glycogen in the liver and muscles, stores fat in adipose tissue, and increases the uptake of amino acids in cells to make proteins.

Glucagon – raises blood glucose levels. Glucagon stimulates gluconeogenesis in the liver and increases fatty acid levels in the blood by breaking down adipose tissue. The effects of insulin and glucagon are nearly opposite to each other. Parathyroid hormones: Parathyroid hormone (PTH) increases renal calcium reabsorption, which increases blood calcium levels.

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Reproduction Video: Reproductive System Introduction Video: Spermatogenesis Video: Egg Development Basics / Oogenesis Video: Reproductive Cycle Graph - Follicular Phase Video: Reproductive Cycle Graph - Luteal Phase Due to the complex nature and various steps of reproduction, it is important that students watch and study the videos for reproduction. The term reproduction refers to the process by which new organisms are produced. The process responsible for the growth of the zygote into a full-formed adult is termed development. Both reproduction and development are fundamental to life.

Male Reproductive System For the GAMSAT, students should know the basic anatomy of both the male and female reproductive system. The male gonads are called testes. Sperm (spermatozoa) is produced in the seminiferous tubules of the testes.

Fig. 85 - Important structures of the male reproductive system. www.acegamsat.com

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Testosterone is an androgen and released from the Leydig cells. This androgen (sex hormone) stimulates the germ cells to become sperm. Testosterone also causes the development of secondary sex characteristics such as the growth of the penis, pubic hair, and enlargement of the larynx (Adam’s apple).

Fig. 86 - The influence of testosterone.

The sperm complete their maturation in the epididymis where they remain collected and stored. Upon ejaculation, the spermatozoa are propelled through the vas deferens and into the urethra and out of the penis. Fluid from the seminal vesicles and the prostate gland combine with the spermatozoa to form semen, which exits the penis upon ejaculation.

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Fig. 87 - Sperm production.

Female Reproductive System The female gonads are called the ovaries. These lie in the pelvic cavity and connect to the uterus via the fallopian tubes. The uterus is a muscular organ, and the end of this organ (the cervix) protrudes into the vagina. The vagina leads to the external genitalia.

Fig. 88 - Important structures of the female reproductive system. www.acegamsat.com

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The vulva includes various glands, openings of the vagina, and folds of skin called the labia majora (large) and labia minora (small). The clitoris is found at the anterior end of the vulva.

Fig. 89 - External structures of the female reproductive system.

The release of an egg (oocyte) from the ovaries of a female is a detailed process. Students should understand the general steps that occur and these are best learned visually (refer to the videos from this chapter).

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The Digestive and Excretory System Video: Gastrointestinal Tract Video: Small Intestine Structure Video: Small Intestine Digestion Video: Colon, Rectum, and Anus Video: Kidney Function and Anatomy Video: The Kidney and Nephron Digestion involves the breakdown of ingested food, allowing nutrients to be absorbed into the body. In terms of the GAMSAT, students should be familiar with the basic anatomy of the digestive system. This includes the mouth, oesophagus, stomach, small intestine, large intestine, rectum, and anus.

Fig. 90 - Important structures of the digestive system. www.acegamsat.com

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Mouth and Oesophagus Digestion begins with an enzyme found in saliva called α-amylase. This enzyme begins breaking down starch into polysaccharides. Chewing is a mechanical process that increases the surface area of food, allowing more enzymes to act on the food at a time. Food that is chewed forms a clump in the mouth called a bolus. The bolus is pushed through the oesophagus via swallowing and then is pushed down the oesophagus by the peristaltic (wave-like) motion of smooth muscles.

The Stomach The bolus moves from the oesophagus into the stomach. The stomach mixes the food and turns it into chyme.

Fig. 91 - Digestion in the stomach via pepsin.

The stomach has an enzyme called pepsin, which initiates protein digestion. The pH of the stomach is 2, which helps kill bacteria that are ingested.

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The Small Intestine

Most of the digestion and absorption occurs in the small intestine. The small intestine is divided into three parts - duodenum, jejunum, and ileum (smallest to largest).

Fig. 92 - Anatomy of the small intestine.

The wall of the small intestine contains villi, which increase the surface area and allow for greater absorption and digestion.

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Fig. 93 - A close look at villi and microvilli of the intestine.

Each villus contains microvilli, which further increase the surface area of the intestinal wall. The pH of the small intestine is 7.6.

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The Pancreas The fluid in the duodenum has a pH of 6 due to the bicarbonate ion secreted by the pancreas.

Fig. 94 - Major components of the pancreas.

The pancreas also releases enzymes that degrade certain macromolecules.

Fig. 95 - Functions of enzymes from the pancreas and liver. www.acegamsat.com

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The enzymes released include: Trypsin and chymotrypsin: degrades proteins into smaller polypeptides. Pancreatic amylase: hydrolyses/digests polysaccharides to trisaccharides and disaccharides. Hydrolysis continues via pancreatic amylase to form small glucose polymers. Lipase: Degrades fats such as triglycerides.

The Liver and Gall Bladder The liver produces bile, which is stored in the gall bladder.

Fig. 96 - Components of the liver.

The gall bladder releases bile to break down fat into small particles without changing the chemical nature of the fat. The liver is important for carbohydrate, fat, and protein metabolism.

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Carbohydrate Metabolism: It is important to maintain the concentrations of glucose in the blood within a narrow, normal range. When excess glucose enters the blood after a meal, it is rapidly taken up by the liver and converted into glycogen. This process is termed glycogenesis. Later, when the concentration of glucose in the blood decreases, the liver activates certain pathways to break down the glycogen (glycogenolysis) back to glucose. The glucose is then transported back into the blood to nourish all other tissues. When the glycogen reserves are exhausted, the liver starts to break down amino acids to form glucose for energy. This process is termed gluconeogenesis.

Fat Metabolism: The liver actively breaks down fats/triglycerides to produce energy. When the liver uses fats for energy, acidic ketone bodies are produced. Students should remember that the pH decreases (more acidic) when the liver uses fats for energy. The liver is also the major site for converting excess carbohydrates and proteins into fatty acids and triglycerides. These are then exported and stored in adipose tissue as fat.

Protein Metabolism: The liver can deaminate amino acids and then convert the non-nitrogenous part of the molecules to lipids and glucose. The liver also functions to remove ammonia from the body via the synthesis of urea. The liver is also responsible for the synthesis of plasma proteins such as albumin.

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The Large Intestine The large intestine is important for water absorption and electrolyte balance. It has four different parts – ascending colon, transverse colon, descending colon, and sigmoid colon.

Fig. 97 - Major components of the large intestine.

Absorption The function of the digestive tract is to convert ingested food into nutrients that are absorbed in the small intestine. The nutrients are absorbed by the enterocytes and then processed and carried to individual cells to be utilized.

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Fats, proteins, and carbohydrates break down into their respective components in the digestion and absorption process.

Fig. 98 - Digestion and absorption of nutrients.

GENERAL RULES: - The fate of proteins - amino acids. - The fate of carbohydrates - glucose. - The fate of fats - triglycerides and fatty acids.

The Kidney The kidney has two major functions: - Maintain homeostasis of solute composition and body fluid volume. - Excrete waste products such as urea, ammonia, uric acid, and phosphate.

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There are two kidneys in the body, each of which is composed of an outer cortex and inner medulla.

Fig. 99 - Anatomy of the kidney.

Urine is created by the kidney, which moves into the renal pelvis. Urine moves from the renal pelvis to the bladder via the ureters. The urine is drained from the bladder via the urethra.

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Kidney Function The main functioning unit of the kidney is the nephron.

Fig. 100 - Components of the nephron.

Blood flows into the capillary bed called the glomerulus (inside Bowman’s capsule). Blood cells and large proteins are filtered out at the glomerulus and the filtrate moves to the proximal tubule. Reabsorption of glucose, proteins, solutes, and water takes place at the proximal tubule. Drugs, toxins, and uric acid are secreted into the filtrate at the proximal tubule. The main role at the proximal tubule is to reduce the amount of filtrate in the nephron without changing the osmolarity. The filtrate moves from the proximal tubule to the loop of Henle. The role of the loop of Henle is to increase solute concentration and osmotic pressure of the medulla. Water diffuses out of the loop of Henle and into the medulla. Salt then diffuses out of the ascending limb.

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The distal tubule secretes K+ and H+ and reabsorbs Na+ and Ca2+. Aldosterone acts here to increase K+ and Na+ membrane transport proteins. The function of the distal tubule is to lower the osmolarity of the filtrate. The filtrate moves from the distal tubule into the collecting duct. ADH acts at the collecting duct, which allows water to passively diffuse out of the nephron. This concentrates the urine, which then enters into the renal pelvis.

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The Cardiovascular System Video: Circulatory System and the Heart Anatomy of the Cardiovascular System The major components of the cardiovascular system include the heart, blood, and blood vessels. For the GAMSAT, students should be able to trace the flow of blood.

Fig. 101 - The main organs, arteries, and veins of the cardiovascular system.

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Circulation in the body can be split into systemic and pulmonary circulation.

Fig. 102 - Blood flow around the body – systemic and pulmonary circulation.

Systemic circulation Blood is pumped from the left ventricle of the heart and moves through the aorta. The aorta supplies the body by branching into smaller arteries, which then branch into arterioles, and then into small blood vessels called capillaries. Once in the capillaries, the blood is collected into venules, which lead to larger veins. The veins join up to the superior and inferior vena cava, which empty into the right atrium of the heart. Pulmonary circulation Blood is pumped into the right ventricle from the right atrium. The right ventricle then pumps blood to the capillaries of the lungs (oxygenation of blood takes place here) via the pulmonary arteries. Blood returns from the lungs back to the heart via the pulmonary

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veins. The returning blood enters the left atrium, which then pumps blood to the left ventricle.

Heart The heart is a large muscle, which contracts to propel the blood through the heart and around the body. Systole occurs when the ventricles contract and diastole occurs when the atria contract and the rest of the heart is relaxed. The contraction of the heart is controlled by the ANS.

Fig. 103 - The spread of impulses through the heart.

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Specifically, the contraction of the heart is controlled by the sinoatrial node (SA node) in the right atrium. This node spreads contractions to the surrounding muscles via electrical impulses. These impulses spread to the atrioventricular node (AV node) located in between the atria. The AV node is slower to contract, which creates a delay so that the atria can contract and push the blood into the ventricles before they contract. The impulses are spread through the heart via Purkinje fibres.

Blood Vessels

Fig. 104 - Blood vessels in the body – vein and artery.

Arteries: elastic vessels that stretch when filled with blood. They are wrapped in smooth muscle. Arterioles: small vessels that are wrapped in smooth muscle and constrict and dilate to regulate blood pressure. Capillaries: microscopic blood vessels that are one cell thick. Nutrient and gas exchange occurs at the capillaries.

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Fig. 105 - Blood flow through the capillaries.

Veins: veins contain a greater volume of blood than arteries. Blood is pumped at a lower pressure in the veins, so they have a valve system that prevents the backflow of blood.

For the GAMSAT, students should remember that an artery carries blood away from the heart and a vein carries blood toward the heart.

Blood Blood is responsible for transporting nutrients, waste products, and hormones around the body. Blood is a type of connective tissue that also serves to protect the body from injury.

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Blood has four major components – plasma, white blood cells, red blood cells, and platelets.

Fig. 106 - Major elements of the blood – platelets, plasma, red blood cells, and white blood cells.

Plasma: plasma contains the matrix of the blood which includes water, urea, ammonia, inorganic compounds, and proteins. Red blood cells (erythrocytes): disk-shaped cells that transport oxygen and carbon dioxide. These cells are rich in haemoglobin. White blood cells (leukocytes): function to protect the body from foreign invaders. There are different leukocytes or white blood cells found in blood.

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Fig. 107 - The different leukocytes (white blood cells) in blood.

These leukocytes are listed from most to least common. - Neutrophils - Lymphocytes - Monocytes - Eosinophils - Basophils

Note: red blood cells have no organelles and no nucleus. White blood cells contain organelles and a nucleus, but do not contain haemoglobin. Platelets: prevent bleeding by clotting the blood.

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The Respiratory System Video: Introduction to Lungs Video: The Lungs and Pulmonary System The respiratory system allows gaseous exchange between the external environment and the blood. Air from the external environment enters through the nose. The air then travels through the pharynx, larynx, trachea, bronchi, bronchioles, and into the alveoli. The alveoli are important as they allow for the exchange of oxygen with carbon dioxide in the blood.

Fig. 108 - Components of the respiratory system.

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Inspiration occurs when the internal skeletal muscle called the diaphragm contacts. Expiration occurs when the diaphragm relaxes.

Fig. 108 - Movement of the diaphragm and thoracic cavity during inspiration and expiration.

The space inside the nose or the nasal cavity functions to moisten, warm, and filter the incoming air. The mucus moistens the air and the internal hairs filter and trap particles. The pharynx acts as a passageway for air and food. The larynx is the voice box and contains the vocal chords. The trachea is also known as the windpipe. It acts as a passageway to the right and left bronchi, with each bronchus splitting into many bronchioles.

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Fig. 109 - Bronchioles leading to thin-walled air sacs called alveoli.

The bronchioles terminate to become small air sacs called alveoli. These air sacs are the site for the respiratory exchange of gases. Oxygen diffuses into the capillaries and then enters the red blood cells. The red blood cells release carbon dioxide, which diffuses into the alveoli and later expelled during expiration.

Fig. 110 - Alveolus gas exchange of carbon dioxide and oxygen. www.acegamsat.com

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The Lymphatic System Video: Why We Need a Lymphatic System Video: Role of Lymphatic System in Immunity

The lymphatic system is an open system that collects and returns interstitial fluid to the blood. This system recycles interstitial fluid and monitors the blood for infection. Interstitial fluid enters the lymph system by flowing between overlapping cells. Once the interstitial fluid enters, it is called lymph. The system contains one-way valves that prevent the backflow of fluid. The lymph will pass through lymph nodes and eventually drain into one of the large veins at the right lymphatic duct or the thoracic duct. The lymph is then emptied into the right atrium of the heart. Lymph has some very important functions and characteristics: - The lymph is responsible for returning proteins that have leaked out of the blood capillaries and moving them back into the bloodstream. - Lymph contains macrophages and lymphocytes (white blood cells) which are important components of the immunes system

- Lymph carries microorganisms to lymph nodes to be destroyed.

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Fig. 111 - Important features of the lymphatic system.

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The Immune System Video: Types of Immune Responses Video: Inflammatory Response The body protects itself from infectious pathogens and toxins in two different ways: innate immunity and acquired immunity. Innate immunity: non-specific protection from most intruding organisms and toxins. Skin (a barrier), phagocytic cells, and stomach acid are all examples of innate immunity. Acquired immunity: protection against specific organisms or toxins. This is developed after the body is attacked and develops immunity. Inflammation results from injury to tissue. Inflammation involves the dilation of blood vessels and an increase in permeability of capillaries. Inflammation creates a “barrier” around the affected tissue, which inhibits the spread of infection. There are two types of acquired immunity – B cell immunity and T cell immunity. B-cell immunity: This type of immunity is promoted by B lymphocytes. Each B lymphocyte makes a single type of antibody, which recognizes a foreign particle called an antigen. Antibodies are highly specific for their respective antigens. If the B lymphocyte antibody contacts a matching antigen, the B lymphocyte will differentiate into plasma cells and memory B cells. These plasma cells will produce and release free antibodies into the blood. The antibodies work in various ways to destroy the foreign substance (antigen). The first time the immune system is exposed to an antigen is known as the primary response. If the body is exposed to the same antigen after the first time, the presence of memory B cells will result in a faster-acting and more potent response called the secondary response. The secondary response does not usually produce any signs or symptoms. For example, if a person is exposed to a certain influenza virus, they will experience common flu-like symptoms in the primary immune response. When exposed to the same influenza virus in the future, the person will already have memory B cells for that particular strain of the virus, and a potent secondary response will be initiated and no or little symptoms will occur.

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Fig. 112 - Concentration of antibody in primary and secondary immune response. T cell immunity: This process of immunity involves T lymphocytes. T lymphocytes differentiate into T helper cells, suppressor T cells, killer T cells, and memory T cells. T helper cells activate B lymphocytes (B cells) and suppressor T cells. Memory T cells have a similar function to memory B cells. Killer T cells bind to the antigen-carrying cells and directly kill it. These two processes differ as one produces antibody-mediated immunity and the other produces cell-mediated immunity.

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Musculoskeletal System Video: 3 Types of Muscle

There are three types of muscle tissue in the body. These include skeletal muscle, cardiac muscle, and smooth muscle.

Fig. 113 - The three different types of muscle cells.

Skeletal Muscle Skeletal muscle is voluntary muscle tissue that is consciously controlled. It connects one bone to another. A muscle is attached to a bone via a tendon and a bone is attached to another bone via a ligament. A sarcomere is the smallest functional unit of skeletal muscle. Myosin and actin work together to create the contraction in skeletal muscle.

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Cardiac Muscle The human heart is made of cardiac muscle. Cardiac muscle is involuntary and is also composed of sarcomeres. Smooth Muscle Smooth muscle is mostly involuntary. Smooth muscle is found in veins and arteries, the stomach, the intestines, the uterus, the urinary bladder, and in the iris. The smooth muscle contracts or relaxes in response to changes in pH, oxygen and carbon dioxide levels, concentration of ions, and temperature.

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Bone Bone is a living tissue that has various functions. It supports soft tissue, assists in movement, protects internal organs, stores minerals, and produces blood cells.

Fig. 114 - Important bones of the human body.

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Bones contain 3 important cells. Osteoblasts: secrete collagen and organic compounds that are responsible for bone formation. Osteocytes: exchange nutrients and waste materials with the blood. Osteoclasts: resorb bone and release minerals back into the blood.

Fig. 115 - Internal structure of bone and its important cells.

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Spongy bone contains red bone marrow, which is the site of red blood cell development. The spongy bone is the inner bone and is porous. Compact bone contains yellow bone marrow, which is important for fat storage. The compact bone is the outer bone and is rigid.

Fig. 116 - Bone anatomy – spongy and compact bone.

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Cartilage Video: Cartilage Structure Cartilage is a type of connective tissue. It is flexible, resilient, and has great tensile strength. There are three types of cartilage: hyaline, elastic, and fibrocartilage. Hyaline cartilage is found in most joints as it functions to absorb shock. Elastic cartilage is found in the upper ear and epiglottis. Fibrocartilage is found in the intervertebral disks.

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Joints There are three different types of joints that can be structurally classified. Synovial joints: a capsule that is filled with synovial fluid separates the synovial joints. These joints allow for a wide range of movement such as at the knee, hip, and shoulder joints. Fibrous joints: occur between two bones held closely together. Little or no movement occurs here such as between the bones of the skull. Cartilaginous joints: occur between two bones tightly connected by cartilage such as the ribs and sternum. Little or no movement occurs here.

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Integumentary System Video: Integumentary System

Skin

Fig. 117 - The components of the skin.

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The skin is an organ that has many important functions. These are protection, thermoregulation, and excretion. Protection: the skin acts as a physical barrier to chemicals, abrasion, dehydration, and UV radiation. Thermoregulation: skin helps to regulate body temperature. Excretion: water and salts are excreted through the skin. The skin has two main parts – epidermis and the dermis.

The epidermis is a vascular epithelial tissue. It has cells that are important for the sensation of touch, the function of the immune system, and production of keratin. The dermis is connective tissue that is beneath the epidermis. It contains blood vessels, nerves, hair follicles, and glands.

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Homeostasis Video: Negative Versus Positive Feedback Temperature, pH, the concentration of glucose and oxygen, and a range of other factors remain relatively constant in order for cells to function efficiently. The maintenance of a constant internal environment is termed homeostasis. The environment is dynamic in reality but it fluctuates continuously within narrow limits and thus can be termed constant.

Negative Feedback:

Fig. 118 - Negative feedback control system of temperature.

A negative feedback control system is used to maintain internal constancy. Changing conditions are detected by sensors, which feed information to an integrating centre that compares conditions to a set point. Deviations from the set point lead to a response to bring internal conditions back to the set point. Negative feedback to the sensor ends this response. The body responding to cold temperature by shivering is an example of negative feedback.

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Positive Feedback:

Positive feedback mechanisms enhance a change. The effectors drive the value of the controlled variable even further from the set point. Blood clotting is an example of positive feedback. Another example is seen through the release of oxytocin during the birth of a baby. When the contraction of the uterus starts, oxytocin is released which stimulates more contractions and more oxytocin to be released.

Fig. 119 - The release of oxytocin as an example of positive feedback.

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Appendix Macromolecules Video: Introduction to DNA Video: RNA Transcription and Translation

The Cell Video: Parts of a Cell

The Cell Membrane Video: Cell Membrane Introduction Video: Transport across the Cell Membrane Video: Endocytosis and Exocytosis

Energy, Metabolism, and Respiration Video: Glycolysis Video: Krebs / Citric Acid Cycle Video: Electron Transport Chain Video: Enzyme-Induced Fit Model

Mitosis and the Cell Cycle Video: Interphase Video: Mitosis Video: Bacterial Binary Fission

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Sexual Reproduction and Meiosis Video: Comparing Mitosis and Meiosis Video: Chromosomal Crossover in Meiosis I Video: Phases of Meiosis I Video: Phases of Meiosis II

Genetics Video: Introduction to Heredity Video: Punnett Square Video: Sex-linked Traits Video: Alleles and Genes

The Nervous System Video: Anatomy of a Neuron Video: Sodium-Potassium Pump Video: Electronic and Action Potential Video: Synapse Structure Video: Chemical Neuronal Synapses Video: Autonomic Nervous System

Reproduction Video: Reproductive System Introduction Video: Spermatogenesis Video: Egg Development Basics / Oogenesis Video: Reproductive Cycle Graph - Follicular Phase Video: Reproductive Cycle Graph - Luteal Phase

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Digestive and Excretory System Video: Gastrointestinal Tract Video: Small Intestine Structure Video: Small Intestine Digestion Video: Colon, Rectum, and Anus Video: Kidney Function and Anatomy Video: The Kidney and Nephron

The Cardiovascular System Video: Circulatory System and the Heart

The Respiratory System Video: Introduction to Lungs Video: The Lungs and Pulmonary System

The Lymphatic System Video: Why We Need a Lymphatic System Video: Role of Lymphatic System in Immunity

The Immune System Video: Types of Immune Responses Video: Inflammatory Response

The Musculoskeletal System Video: 3 Types of Muscle

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Cartilage Video: Cartilage Structure

Integumentary System Video: Integumentary System

Homeostasis Video: Negative Versus Positive Feedback

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