AQA Biology AS + A Level Revision Guide (New 2015 Spec)

CGP A-Level Biology Exa m B o a rd : A Q A Complete Revision & Practice Fantastic in-depth Student Books for A-Level Science! Unbeatable companions to the AQA and OCR courses — from day one until the final exams! cgpbooks.co.uk • amaZ0n.C0.uk • Waterstones • W HSm ith A - L e v e l Exam Board: AQA Revising for Biology exams is stressful, that's for sure — even just getting your notes sorted out can leave you needing a lie down. But help is at hand... This brilliant C G P book explains everything you'll need to learn (and nothing you won't), all in a straightforward style that's easy to get your head around. W e've also included exam questions to test how ready you are for the real thing. € CGP A-Level revision? It has to be CGP! Published by CGP From original material by Richard Parsons. Editors: Charlotte Burrows, Rachel Kordan, Christopher Lindle, Christopher McGarry, Sarah Pattison, Claire Plowman, Rachael Rogers, Hayley Thompson. Contributors: Sophie Anderson, Gloria Barnett, Jessica Egan, Derek Harvey, Liz Masters, Adrian Schmit. BAR72DF ISBN: 978 1 78294 297 9 With thanks to Ellen Shores, Camilla Simson and Karen Wells for the proofreading. With thanks to Laura Jakubowski for the copyright research. Clipart from Corel” Text, design, layout and original illustrations €) Coordination Group Publications Ltd. (CGP) 2015 All rights reserved. 0800 1712 712 • www.cgpbooks.co.uk Contents If you're revising for the AS exams, you'll need Topics 1 -4, and the Practical Skills section at the back. If you're revising for the A-level exams, you'll need the whole book. Topic 1A — Biological Molecules Topic 2B — Cell Membranes Carbohydrates....................................................................................2 Cell Membrane Structure........................................................ 36 L ip ids......................................................................................................6 Exchange Across Cell Membranes — Diffusion......... 38 Proteins..................................................................................................8 Exchange Across Cell Membranes — Osmosis...........40 Enzyme A ction ............................................................................... 10 Exchange Across Cell Membranes — Active Transport.............................................................. 42 Factors Affecting Enzyme Activ ity ........................................12 Enzyme-Controlled Reactions................................................ 14 Topic 2C — Cells and Topic 1B — More Biological the Immune System Molecules The Immune System....................................................................44 DNA and R N A ...............................................................................16 Immunity and Vaccines............................................................ 46 DNA Replication...........................................................................18 Antibodies in M edicine............................................................ 48 W ater.................................................................................................. 20 Interpreting Vaccine and Antibody Data.......................... 50 A T P .......................................................................................................22 HIV and Viruses..............................................................................52 Inorganic Ions................................................................................. 23 Topic 3A — Exchange and Topic 2A — Cell Structure Transport Systems and Division Size and Surface Area.................................................................. 54 Eukaryotic Cells and Organelles.......................................... 24 Gas Exchange..................................................................................56 Prokaryotic Cells and Viruses..................................................28 Gas Exchange in Humans........................................................ 58 Analysis of Cell Components..................................................30 The Effects of Lung Disease..................................................... 60 Cell Division — Mitosis............................................................. 32 Interpreting Lung Disease Data.............................................62 Cell Division — Investigating Mitosis................................ 34 Dissecting Gas Exchange Systems.......................................64 Topic 3B — More Exchange Topic 5A — Photosynthesis and Transport Systems and Respiration Digestion and Absorption..........................................................66 Photosynthesis, Respiration and ATP.............................104 Haemoglobin..................................................................................68 Photosynthesis............................................................................106 The Circulatory System..............................................................70 Limiting Factors in Photosynthesis.................................110 The H eart...........................................................................................72 Photosynthesis Experiments...............................................112 Cardiovascular D isease.............................................................75 Respiration..................................................................................... 114 Transport in Plants — Xylem ...................................................78 Aerobic Respiration...................................................................115 Transport in Plants — Phloem................................................80 Respiration Experiments.........................................................118 Topic 4A — DNA, RNA and Topic 5B — Energy Transfer Protein Synthesis and Nutrient Cycles DNA, Genes and Chromosomes...........................................82 Energy Transfer in Ecosystems............................................120 RNA and Protein Synthesis...................................................... 84 Farming Practices and Production....................................122 The Genetic Code and Nucleic Acids...............................86 Nutrient Cycles............................................................................124 Fertilisers and Eutrophication............................................. 126 Topic 4B — Diversity, Classification and Variation Topic 6A — Stimuli and Responses Meiosis and Genetic Variation................................................88 Nervous Communication.......................................................128 Mutations.............................................................................................91 Responses in Plants and Anim als......................................130 Genetic Diversity and Natural Selection.......................... 92 Receptors........................................................................................132 Investigating Selection.................................................................94 Control of Heart Rate................................................................134 Classification of Organisms..................................................... 96 DNA Technology, Classification and Diversity..........98 Investigating Variation............................................................ 100 Topic 6B — Nervous Coordination Biodiversity..................................................................................102 Neurones.......................... 136 Synaptic Transmission 139 Muscle Contraction... 142 Topic 6C — Homeostasis Topic 8A — Mutations and Gene Expression Homeostasis Basics................................................................... 146 Control of Blood Glucose Concentration....................148 Mutations.......................................................................................180 The Kidneys...................................................................................152 Cancer.............................................................................................. 182 Controlling Blood Water Potential..................................154 Interpreting Data on C ancer............................................... 184 Stem C e lls ......................................................................................186 Regulation of Transcription and Translation................190 Epigenetic Control of Gene Expression..........................193 Topic 7A — Genetics Evaluating Data on Phenotypes........................................ 195 Inheritance......................................................................................156 Linkage and Epistasis................................................................159 The Chi-Squared Test................................................................ 162 Topic 8B — Genome Projects and Gene Technologies Genome Projects and Making DNA Fragments......196 Topic 7B — Populations and Evolution Amplifying DNA Fragments...................................................199 Using Recombinant DNA Technology..............................201 The Hardy-Weinberg Princip le ........................................164 Gene Probes and Medical Diagnosis.............................. 204 Variation and Selection......................................................... 166 Genetic Fingerprinting............................................................. 206 Speciation and Genetic D rift............................................ 168 Practical Skills Topic 7C — Populations in Ecosystems Planning an Experiment.......................................................... 208 Ecosystems...................................................................................170 Processing and Presenting Data........................................210 Variation in Population Size............................................... 172 Drawing Conclusions and Evaluating.............................213 Investigating Populations..................................................... 174 Succession.................................................................................... 176 Conservation...............................................................................178 Do Well In Your Exams HowTo Do Well in Your Exam s.......................................215 Answers........................ Acknowledgements 230 Index.............................. 231 2 To p ic IA — B io lo g ic a l M o lec u les Carbohydrates Even though there is, and has been, a huge variety o f different organisms on Earth, they all share some biochemistry — for example, they all contain a few carbon-based compounds that interact in similar ways. Most Carbohydrates are Polymers monomer e.g. monosaccharide, amino acid 1) Most carbohydrates (as well as proteins and nucleic acids) are polymers. 2) Polymers are large, complex molecules composed of long chains of '= 4 h r monomers joined together. polymer e.g. carbohydrate, protein 3) Monomers are small, basic molecular units. 4) Examples of monomers include monosaccharides, amino acids and nucleotides. Carbohydrates are Made from Monosaccharides 1) All carbohydrates contain the elements C, H and O. 2) The monomers that they're made from are monosaccharides, e.g. glucose, fructose and galactose. 1) Glucose is a hexose sugar — a monosaccharide with six carbon atoms in each molecule. 2) There are two types of glucose, alpha (a) and beta (|3) — they're isomers (molecules with the same molecular formula as each other, but with the atoms connected in a different way). 3) You need to know the structures of both types of glucose for your exam — it's pretty easy because there's only one difference between the two: a-glucose molecule P-glucose molecule C H ,O H C H 2O H i 2 H O H \ /h \ r \ \ A ~ \ r HOn / \?c -H- -cv k\ O H / I ho/ Vh i, i \ / I I H O H V H O H ^ T h e two types of glucose have these groups reversed Condensation Reactions Join Monosaccharides Together 1) A condensation reaction is when two molecules join together with the formation of a new chemical bond, and a water molecule is released when the bond is formed. 2) Monosaccharides are joined together by condensation reactions. 3) A glycosidic bond forms between the two monosaccharides as a molecule of water is released. 4) A disaccharide is formed when two monosaccharides join together. Example glycosidic bond Two a-glucose H O. /H H H O /H + H,0 molecules are HO o;h HO OH HO l Q'1 OH joined together by a-glucose a-glucose maltose a glycosidic bond to form maltose. H O is removed 1 M l M M I I I I I n I I I I I ^ If you're asked to show a t 5) Sucrose is a disaccharide formed from a condensation reaction between a Z condensation reaction, don't ~ -- forget to put the water I glucose molecule and a fructose molecule. z molecule in as a product. r 6) Lactose is another disaccharide formed from a glucose molecule and a 11111111 n 11 n 1/ 11 ii 11 galactose molecule. To p ic 1A — B io l o g ic a l M o l e c u l e s 3 Carbohydrates Hydrolysis Reactions Break Polymers Apart 1) Polymers can be broken down into monomers by hydrolysis reactions. 2) A hydrolysis reaction breaks the chemical bond between monomers using a water molecule. It's basically the opposite of a condensation reaction. 3) For example, carbohydrates can be broken down into their constituent monosaccharides by hydrolysis reactions. Polymer Hydrolysis — the bond is broken by the A addition of a water molecule Even hydrolysis couldn't break this bond. -O H H O - -O H Use the Benedict’s Test for Sugars Sugar is a general term for monosaccharides and disaccharides. All sugars can be classified as reducing or non-reducing. The Benedict's test tests for sugars — it differs depending on the type of sugar you are testing for. 1) Reducing sugars include all monosaccharides (e.g. glucose) and some disaccharides (e.g. maltose and lactose). 2) You add Benedict's reagent (which is blue) to a sample and heat it in a water bath that's been brought to the boil. 3) If the test's positive it w ill form a coloured precipitate (solid particles suspended in the solution). r Alwar s us« an excess of r Z Benedict's solution — ; The colour of the precipitate changes from: Z thls mak« sure that all ~ Z the sugar reacts. z 1 1 1 " I I I I I I M M | | | V\N blue-£> green>=>-yellowH>orange=4> brick red 4) The higher the concentration of reducing sugar, the further the colour change goes — you can use this to compare the amount of reducing sugar in different solutions. A more accurate way of doing this is to filter the solution and weigh the precipitate. C d/£1 1) If the result of the reducing sugars test is negative, there could still be a < non-reducing sugar present. To test for non-reducing sugars, like sucrose, U D first you have to break them down into monosaccharides. 1X1 U 2) You do this by getting a new sample of the test solution, adding dilute Z hydrochloric acid and carefully heating it in a water bath that's been u D brought to the boil. You then neutralise it with sodium hydrogencarbonate. OLU Then just carry out the Benedict's test as you would for a reducing sugar. I 3) If the test's positive it w ill form a coloured precipitate (as for the reducing z O sugars test). If the test's negative the solution will stay blue, which means it doesn't contain any sugar (either reducing or non-reducing). To p ic 1A — B io l o g ic a l M o l e c u l e s 4 Carbohydrates So, you've already looked at monosaccharides and disaccharides... now it's time to give polysaccharides some love. Polysaccharides are Loads of Sugars Joined Together A polysaccharide is formed when more than two monosaccharides are joined together by condensation reactions. a-glucose a-glucose a-glucose a-glucose a-glucose You need to know about the relationship between the structure and function of three polysaccharides — starch, glycogen and cellulose. Starch is the Main Energy Storage Material in Plants 1) Cells get energy from glucose. Plants store excess glucose as starch (when a plant needs more glucose for energy, it breaks down starch to release the glucose). 2) Starch is a mixture of two polysaccharides of alpha-glucose — amylose and amylopectin: • Amylose — a long, unbranched chain of a-glucose. The angles of the glycosidic bonds give it a coiled structure, almost like a cylinder. This makes it compact, one amlpohleac-uglelucose so it's really good for storage because you can fit more in to a small space. • Amylopectin — a long, branched chain of a-glucose. Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily. This means that the glucose can be released quickly. Amylopectin 3) Starch is insoluble in water and doesn't affect water potential (see page 40), so it doesn't cause water to enter cells by osmosis, which would make them swell. This makes it good for storage. Use the Iodine Test for Starch If you do any experiment on the digestion of starch and want to find out if any is left, you'll need the iodine test. just add iodine dissolved in potassium iodide solution to the test sample. If there is starch present, the sample changes from browny-orange to a dark, blue-black colour. Glycogen is the Main Energy Storage Material in Animals 1) Animal cells get energy from glucose too. Glycogen But animals store excess glucose as glycogen — another polysaccharide of alpha-glucose. 2) Its structure is very similar to amylopectin, except that it has loads more side branches coming off it. Loads of branches means that stored glucose can be released quickly, which is important for energy release in animals. After throwing and fetching 3) It's also a very compact molecule, the ball no less than 312 so it's good for storage. times, Chappy and Stuart were finally out of glycogen. To p ic 1A — B io l o g ic a l M o l e c u l e s