AQA GCSE Biology Revision Guide 2016 PDF

Ketet}> Biology ey AQA (Grade 9-1) y New! The Revision Guide Sen baXolttlo(-t-m m-7-M@salibal-Waxebtateyal ' For the new course starting September 2016  What to Expect in the Exams fore you get cracking with you...

Ketet}> Biology ey AQA (Grade 9-1) y New! The Revision Guide Sen baXolttlo(-t-m m-7-M@salibal-Waxebtateyal ' For the new course starting September 2016  What to Expect in the Exams fore you get cracking with your revision, here's a handy guide to what youll have to face in the exams - and the special features of this book that we've included especially to help you. Youre welcome. (a) Topics are Covered in Different Papers For GCSE Biology, you'll sit two exam No. of marks Topics Assessed papers at the end of your COU’. ———> 1 hr 45 mins (Re Beeline CAT LIE AAV LAT pe titer = You're expected to know the basic 1 hr 45 mins 100 5,6 and 7 papers. = concepts of biology in both in nin we es i W e r Sr (2) There are Different Question Types In each exam, you'll be expected to answer a mixture of multiple choice questions, structured questions, questions that have short, closed answers as well as open response questions. For some open response questions, you'll be Always make sure: marked on the OM overall quality of your answer, ! AEM LEMS sh -Vauanewer the question fully. ——y> ot [Msi i>: seleniilierconten aes * You include detailed, relevant information. * Your answer is clear and has a logical structure. | (3) You’ll be Tested on your Maths... At least 10% of the total marks for GCSE Biology Look out for these worked examples in this book will come from questions that test your maths skills. — they show you maths skills you'll need in the exam. For these questions, always remember to: * Show your working — you could get marks for this, even if your final answer's wrong. * Check that the units of your answer are the same as the ones they asked for in the question. * Make sure your answer is given to an appropriate number of significant figures. (4)...and on your Practical Skills * GCSE Biology contains 10 required practical activities that you'll do during the course. Whenever one of the required practical activities crops up in You can be asked about these, and the practical skills involved in them, in the exams. this book, its marked up like * At least 15% of the total marks will be for questions that test your ee understanding of the practical activities and practical skills. PRACTICAL * For example, you might be asked to comment on the design of an experiment sand teres a whGlersechion on (the apparatus and method), make predictions, analyse or interpret results... Practical Skills on pages 126-130. Pretty much anything to do with planning and carrying out the investigations. | (5) You’ll need to know about Working Scientifically | Working Scientifically is all about how science is applied in the outside world by real scientists. Whe STAIN Tallis) For example, you might be asked about ways that scientists communicate an idea to get = Working Scientifically Pi2 their point across without being biased, or about the limitations of a scientific theory. 5,POCO ,CoveredDUG on Gpages 1-10, = § iciy gp You need to think about the situation that you've been given and use all your scientific savvy to answer the question. Always read the question and any data you've been given really carefully before you start writing your answer.  aC i books fn Ps ilike ike ng Others ilJ — CAF, Get organ-ised for Biology with CGP... There's a lot to learn in GCSE Biology, that's for sure. Luckily, this CGP book explains the facts, theory and practical skills you'll need — with practice questions on each page to test you on what you've learned. How to access your free Online Edition awewt This book includes a free Online Edition to read on your PC, Mac or tablet. To access it, just go to cgpbooks.co.uk/extras and enter this code... Ee ai eR By the way, this code only works for one person. If somebody else has used this book before you, they might have already claimed the Online Edition. CGP — still the best! © Our sole aim here at CGP is to produce the highest quality books — carefully written, immaculately presented and dangerously close to being funny. Then we work our socks off to get them out to you — at the cheapest possible prices.  Contents | Working Scientifically Transpiration and Translocation wmunenneneeeeeie 43 FS clerate IVA EIIOG «cam soteecincconetegtacarectoneeneee cence ata| Transplratiorieand StOmatayan ayer tee socaete AS Communication & Issues Created by Schence.rcmencee , Revision Questions fot TOC 2 aa. sansa scan nneriteaS FRITS toeon dlecrracsltyect a Uirestaci oe anetteee 5 Designing Investig atons.etcn.tccmiccns/camtsconioiees caiman 4 Topic 3 — Infection and Response Collecting’ Data. icin depenataeeierneee een amen ES Geinmrunicable: Disease. accu atte eee eee 46 Processing anid Presenting Data iacrccnecrasnnnnsoaaem 6 Vitaielecngal and Protist Diseases.2.c.ac5e canons 4k Uinits-and: Equationsiciicrc:.cteeonacune se nee 8 Bacterial Diseases and Preventing Disease smn 48 Drawing Conclusions sy.tinecdcesncatadaiteiccctat tame ame 2) HC) WEEESEis ishssosseliecinan Seadoo uae nes eee 4g Wheertainties and Eval Uations....,aacmeer eno eee 10 Fighting Disease — Vaccinatiotin.1n.00 114 ae eee atANTScop amsmitosouecmametont nents 92 Fei oes g2 ReBea 0gene. er ee 115 Inherited Disorders. Kiron Mati Bechevanon93 Biodiversity and Waste Managements 116 a rere ob Vieridel cx bess dct daatannsistevean iinidaiudtshace 94 Salesian ATTN esae ecg cl rencsncrdene 117 COE Can 2 72 Ae a a eR. core 95 POCTOPESCATION GPa APIA SE sions incasorvosionscoocncgaditinse 118 aL ae Neareleen.. SW Misedbleat acorn PS ee OREM) 96 Maintaining Ecosystems and Biodiversity... 119 Seat PIC LEVOPLDCNITY oe cect vigstacncociseeraastinscareuerincioerne 7 5 EFSaccaae teen paper sc ees seers 120 eRe EO WO ascareaienaiininapouencdbnsgainaGncditsnas nese98 DLE ike@=|[21Gy See eee ee ye 121 (CORES1A STISGT Re on? NE ft rE a0 FiferCoege (ee enc Pa a122 PaONT irer esas Sactele. style dnedibltg Ta wetaiten ci bek 100 ecemeicebigiig Ur Warlaqt) Ll: [ereercrek eer eee 123 Ce ae Ons oe ee eT 101 Bickeennciay ase. ea eee. ee ee ee 124 SCC ie eee. Ce 102 Revision Questions for Topic 7 eemuummsmamsnasnnsnsnse WS SOICHIIC GKOSISEAIGE BACEEMavnsnccnssinscinutesensatnenniannesn 103 re) oe cas hn a a eo eon Mae 104 Practical Skills EWISION CJUESTIONS TOF JODIE ©. cinneiiassauonsiepamnnins 105 PHNCESUIFPIEL SUNS ATTORS accesses otaerenstto enon stderr 126 PICAUING, SETECy AN UNIO Rodi caieeeen sea 127 Potometers and MiCrOSCOPES.cc:mmnsnrrrmrmnonirioar ene128 CFLi ne an nnn ees... 129 Me Tier Tgp CaNees esc r ae) eee 130 NPIS WEIS coos 5 omc arses caret oan eget 131 Published by CGP From original material by Richard Parsons Editors: Charlotte Burrows, Katherine Faudemer, Chris McGarry and Sarah Pattison Contributor: Paddy Gannon With thanks to Hayley Thompson and Sophie Anderson for the proofreading. Printed by Elanders Ltd, Newcastle upon Tyne. Clipart from Corel” Text, design, layout and original illustrations © Coordination Group Publications Ltd (CGP) 2016 All rights reserved. Photocopying more than one chapter of this book is not permitted. Extra copies are available from CGP. 0800 1712 712 -* www.cgpbooks.co.uk  Working Scientifically l This section isn't about how to ‘do’ science — but it does show you the way most scientists work. 1) Scientists try to explain things. They start by observing something they don't understand. 2) They then come up with a hypothesis — a possible explanation for what they've observed. 3) The next step is to test whether the hypothesis might be right or not. This involves making a prediction based on the hypothesis and testing it by gathering evidence (i.e. data) from investigations. If evidence from experiments backs up a prediction, you're a step closer to figuring out if the hypothesis is true. Hundreds of years ago, we thought demons hae W73114 Tn caused illness. og WET a Bete io v {Iii i est da £1 4 VPotL lies y my a 4 £ aye i 1) Normally, scientists share their findings in peer-reviewed journals, or at conferences. 2) Peer-review is where other scientists check results and scientific explanations to make sure they're ‘scientific’ (e.g. that experiments have been done in a sensible way) before they're published. It helps to detect false claims, but it doesn't mean that findings are correct — just that they're not wrong in any obvious way. 3) Once other scientists have found out about a hypothesis, they'll start basing their Then we thought it was own predictions on it and carry out their own experiments. They'll also try to caused by ‘bad blood’ (and treated it with leeches) reproduce the original experiments to check the results — and if all the experiments in the world back up the hypothesis, then scientists start to think the hypothesis is true. 4) However, if a scientist does an experiment that doesn't fit with the hypothesis (and other scientists can reproduce the results) then the hypothesis may need to be modified or scrapped altogether. 1) accepted theories are the ones that have survived this ‘trial by evidence’ — they've been tested many times over the years and survived. 2) However, theories never become totally indisputable fact. If new evidence comes along that can't be explained using the existing theory, then the hypothesising and testing is likely to start all over again. Now weve collected more evidence, we know that illnesses that can be spread between people are Jizzerent niet gia tagtct A ad! I Mt VvpeE bi 01 ctLVioaels tea — | due to microorganisms. 1) A representational model is a simplified description or picture of what's MHEUEELEEUUP erty going on in real life. Like all models, it can be used to explain observations = °cientists test models by carrying = and make predictions. E.g. the lock and key model of enzyme action ingi.in 8 : : i preaictions made by the model is a simplified way of showing how enzymes work (see p.28). It can Nun aa/ happen as expected be used to explain why enzymes only catalyse particular reactions. MIMI tary 2) Computational models use computers to make simulations of complex real-life processes, such as climate change. They're used when there are a lot of different variables (factors that change) to consider, and because you can easily change their design to take into account new data. 3) All models have limitations on what they can explain or predict. Climate change models have several limitations — for example, it's hard to take into account all the biological and chemical processes that influence climate. It can also be difficult to include regional variations in climate. I’m off to the zoo to test my hippo-thesis... | The scientific method has been developed over time, and many people have helped to develop it. From Aristotle | to modern day scientists, lots of people have contributed. And many more are likely to contribute in the future. Working Scientifically  Gare scientifiic Fetorarceeae that people should eiarae their ents ormen might Provide eee that could be developed into new technology. So scientists need to tell the World about their discoveries. Gene technologies are used in genetic engineering to produce genetically modified crops. Information about these crops needs to be communicated to farmers who might benefit from growing them and to the general public, so they can make informed decisions about the food they buy and eat. y enter adlin. aiBias ased Way _ 1) rater Sout eeeic sega in the a (e.g. newspapers or television) aren't peer-reviewed. 2) This means that, even though news stories are often based on data that has been peer-reviewed, the data might be presented in a way that is over-simplified or inaccurate, making it open to misinterpretation. 3) People who want to make a point can sometimes present data in a biased way. (Sometimes without knowing they're doing it.) For example, a scientist might overemphasise a relationship in the data, or a newspaper article might describe details of data supporting an idea without giving any evidence against it. acorn c inondedoeis poeeed ibid dob ears And this Peale eatics to scientific developments, e.g. new technologies or new advice. These developments can create issues though. For example: Economic issues: Society can't always Social issues: Decisions based on scientific evidence afford to do things scientists recommend affect people — e.g. should alcohol be banned (e.g. investing in alternative energy (to prevent health problems)? Would the effect on sources) without cutting back elsewhere. people's lifestyles be acceptable...? Personal issues: Some decisions will affect Environmental issues: Human activity often affects the individuals. For example, someone might natural environment — e.g. genetically modified crops may support alternative energy, but object ifa —_ help us to produce more food — but some people think wind farm is built next to their house. they could cause environmental problems (see p.99). sage A ae Cee ae ae = vn biA nswe: — aah1% ot etaliera ite Weer arate Sf oyGirerateee ‘an’ " t obs Ansi = A = J! 1) We Hong aaderetand Saal We’ re “einefiSingsott more, isuweell never n ence all the answers. 2) In order to answer scientific questions, scientists need data to provide evidence for their hypotheses. 3) Some questions can't be answered yet because the data can't currently be collected, or because there's not enough data to support a theory. 4) Eventually, as we get more evidence, we'll answer some of the questions that currently can't be answered, e.g. what the impact of global warming on sea levels will be. But there will always be the "Should we be doing this at all?"-type questions that experiments can't help us to answer... Think about new drugs which can be taken to boost your ‘brain power’. * Some people think they're good as they could improve concentration or memory. New drugs could let people think in ways beyond the powers of normal brains. * Other people say they're bad — they could give you an unfair advantage in exams. And people might be pressured into taking them so that they could work more effectively, and for longer hours. Tea to milk or milk to tea? — Totally unanswerable by science... Science can’t tell you whether or not you should do something. That’s for you and society to decide. But there are tons of questions science might be able to answer, like where life came from and where my superhero socks are. Working Scientifically By reading this page you are agreeing to the risk of a paper cut or severe drowsiness... 1) A hazard is something that could potentially cause harm. 2) All hazards have a risk attached to them — this is the chance that the hazard will cause harm. 3) The risks of some things seem pretty obvious, or we've known about them for a while, like the risk of causing acid rain by polluting the atmosphere, or of having a car accident when you're travelling in a car. 4) New technology arising from scientific advances can bring new risks, e.g. scientists are unsure whether nanoparticles that are being used in cosmetics and suncream might be harming the cells in our bodies. These risks need to be considered alongside the benefits of the technology, e.g. improved sun protection. 5) You can estimate the size of a risk based on how many times something happens in a big sample (e.g. 100000 people) over a given period (e.g. a year). For example, you could assess the risk of a driver crashing by recording how many people in a group of 100000 drivers crashed their cars over a year. 6) To make decisions about activities that involve hazards, we need to take into account the chance of the hazard causing harm, and how serious the consequences would be if it did. If an activity involves a hazard that's very likely to cause harm, with serious consequences if it does, it's considered high risk. 1) Not all risks have the same consequences, e.g. if you chop veg with a sharp knife you risk cutting your finger, but if you go scuba-diving you risk death. You're much more likely to cut your finger during half an hour of chopping than to die during half an hour of scuba-diving. But most people are happier to accept a higher probability of an accident if the consequences are short-lived and fairly minor. 2) People tend to be more willing to accept a risk if they choose to do something (e.g. go scuba diving), compared to having the risk imposed on them (e.g. having a nuclear power station built next door). 3) People's perception of risk (how risky they think something is) isn't always accurate. They tend to view familiar activities as low-risk and unfamiliar activities as high-risk — even if that's not the case. For example, cycling on roads is often high-risk, but many people are happy to do it because it's a familiar activity. Air travel is actually pretty safe, but a lot of people perceive it as high-risk. 4) People may over-estimate the risk of things with long-term or invisible effects, e.g. ionising radiation. Hazards from science experiments might include: ° Microorganisms, e.g. some bacteria can make you ill. * Chemicals, e.g. sulfuric acid can burn your skin and alcohols catch fire easily. ¢ Fire, e.g. an unattended Bunsen burner is a fire hazard. * Electricity, e.g. faulty electrical equipment could give you a shock. 2) Part of planning an investigation is making sure that it's safe. 3) You should always make sure that you identify all the hazards that you might encounter. — Then you should think of ways of reducing the risks from the hazards you've identified. For example: If you're working with sulfuric acid, always wear gloves and safety goggles. This will reduce the risk of the acid coming into contact with your skin and eyes. \/'' i iiiiiriiitiviyy, You can find ¢ If you're using a Bunsen burner, stand it on a heat proof mat. out about potent tial |hazards \ pot ial 64 ih chase viek of starting aye by looking in textbooks, doing some Cele per internet research, or asking your L ry EOS teacher SOE a ee Taam eee On eee SFLU EAN Not revising — an unacceptable exam hazard... The world’s a dangerous place, but if you can recognise hazards, decide how to reduce their risks, and be happy to accept some risks, you can still have fun. Just maybe don’t go skydiving with a great white shark on Friday 13th. Working Scientifically  a _ Designing Investi zati 01 RIL ELI OT EER NR I investigation time. Dig out your lab coat and dust down your badly-scratched safety oleae it's ;Investigations |Produce Evidence to Support orr Disprot ! 1) Scientists observe things and come up with hypotheses to explain them (see p.1). You need to be able to do the same. For example: Observation: People have big feet and spots. Hypothesis: Having big feet causes spots. 2) To determine whether or not a hypothesis is right, you need to do an investigation to gather evidence. To do this, you need to use your hypothesis to make a prediction — something you think will happen that you can test. E.g. people who have bigger feet will have more spots. 3) Investigations are used to see if there are patterns or relationships between two variables, e.g. to see if there's a pattern or relationship between the variables ‘number of spots’ and 'size of feet'. cEvidence Needs to bee Repeatable, Reproducible a and’ VLE RTT 1) Repeatable means that ifthe same person does an experiment again said Investigations the same methods and equipment, they'll get similar results. include experiments 2) Reproducible means that if someone else does the experiment, or a different Sent iyee and hatistudies, Sa PANS LAER method or piece of equipment is used, the results will still be similar. 3) If data is repeatable and reproducible, it's reliable and scientists are more likely to have confidence in it. 4) Valid results are both repeatable and reproducible AND they answer the original question. They come from experiments that were designed to be a FAIR TEST... see go, eee -Uae _ToMake an Investigation a Fair Test You Have to Control the Variables 1) In a lab experiment you usually change one variable and measure how it affects another variable. 2) To make it a fair test, everything else that could affect the results should stay the same — otherwise you can't tell if the thing you're changing is causing the results or not. 3) The variable you CHANGE is called the INDEPENDENT variable. 4) The variable you MEASURE when you change the independent variable is the DEPENDENT variable. 5) The variables that you KEEP THE SAME are called CONTROL variables. You could find how temperature affects the rate of an enzyme-controlled reaction. The independent variable is the temperature. The dependent variable is the rate of reaction. Control variables include the concentration and amounts of reactants, pH, the time period you measure, etc. 6) Because you can't always control all the variables, you often need to use a control experiment. This is an experiment that's kept under the same conditions as the rest of the investigation, but doesn't have anything done to it. This is so that you can see what happens when you don't change anything at all. Ps‘Thee Bigger the Sample Sizethe Better ob Kaban ‘ 1) Data based on small samples isn't as good as data based on large samples. A sample should represent the whole population (i.e. it should share as many of the characteristics in the population as possible) — a small sample can't do that as well. It's also harder to spot anomalies if your sample size is too small. 2) The bigger the sample size the better, but scientists have to be realistic when choosing how big. For example, if you were studying how lifestyle affects people's weight it'd be great to study everyone in the UK (a huge sample), but it'd take ages and cost a bomb. It's more realistic to study a thousand people, with a mixture of ages, gender and race. Nero Sus os as ms A : ee fe _ This is no high street survey — it’s a designer investigation... Not only do you need to be able to plan your own investigations, you should also be able to look at someone else’s plan and decide whether or not it needs improving. Those examiners aren’t half demanding. Working Scientifically  1) To check ant you need to repeat the re 5d eel that the results are Ear You need to repeat each reading at least three times. 2) To make sure your results are reproducible you can cross check them by taking a second set of readings with another instrument (or a different observer). Brian's result 3) Your data also needs to be ACCURATE. Really accurate results are those was a Curate that are really close to the true answer. The accuracy of your results usually depends on your method — you need to make sure you're measuring the right thing and that you don't miss anything that should be included in the measurements. E.g. estimating the amount of gas released from a reaction by counting the bubbles isn't very accurate because you might miss some of the bubbles and they might have different volumes. It's more accurate to measure the volume of gas released using a gas suringe. Data set 1is more precise than data set 2 4) Your data also needs to be PRECISE. Precise results are ones where the data is all really close to the mean (average) of your phe results (i.e. not spread out). 1) The measuring erates you use eelto be sensitive enough to measure the changes you're looking for. For example, if you need to measure changes of 1 cm® you need to use a measuring cylinder that can measure in 1 cm? steps — it'd be no good trying with one that only measures in 10 cm steps. 2) The smallest change a measuring instrument can detect is called its RESOLUTION. E.g. some mass balances have a resolution of 1 g, some have a resolution of 0.1 g, and some are even more sensitive. 3) Also, equipment needs to be calibrated by measuring a known value. If there's a difference between the measured and known value, you can use this to correct the inaccuracy of the equipment. 1) The renhiteatyour AgRE er will Peevary a bit persed of RANDOM ERRORS — unpredictable differences caused by things like human errors in measuring. E.g. the errors you make when reading from a measuring cylinder are random. You have to estimate or round the level when it's between two marks — so sometimes your figure will be a bit above the real one, and sometimes it will be a bit below. SUE EEE DT bh. 2) You can reduce the effect of random errors by taking repeat readings = If there's no systematic error, and finding the mean. This will make your results more precise. then doing repeats and 3) If a measurement is wrong by the same amount every time, it's called calculating a mean can make a SYSTEMATIC ERROR. For example, if you measured from the very iby hater nL Atay JEEP end of your ruler instead of from the O cm mark every time, all your measurements would be a bit small. Repeating the experiment in the exact same way and calculating a mean won't correct a systematic error. 4) Just to make moce more complicated, if a systematic error is caused by using equipment that isn't zeroed properly, it's called a ZERO ERROR. For example, if a mass balance always reads | gram before you put anything on it, all your measurements will be 1 gram too heavy. 5) You can compensate for some systematic errors if you know about them though, e.g. if your mass balance always reads | gram before you put anything on it you can subtract | gram from all your results. 6) Sometimes you get a result that doesn't fit in with the rest at all. This is called an ANOMALOUS RESULT. You should investigate it and try to work out what happened. If you can work out what happened (e.g. you measured something totally wrong) you can ignore it when processing your results. Watch what you say to that mass balance — it’s very sensitive... Weirdly, data can be really precise but not very accurate. For example, a fancy piece of lab equipment might give results that are really precise, but if it’s not been calibrated sank those results won’t be accurate. Working Scientifically  ee Pres at Processing and ' PY tie. Me te ein 2.) Se ee, Ea aes Be j a 4 ‘7 ye ee. Z =) = ee u rule on cs wee = aewee aad a ee Processing your data means doing some calculations with it to make it more useful. Once you've done that, you can present your results in a nice chart or graph to help you spot any patterns in your data. |Data Needs to be Organised j Tables are dead useful for organising data. When you draw a table use a ruler and make sure each column has a heading (including the units). You Might Have to Process Your Data 1) When you've done repeats of an experiment you should always calculate the mean (a type of average). To do this add together all the data values and divide by the total number of values in the sample. Den Sat lite alist ee 2) You might also need to calculate the range (how spread out the data is). lamas aera To do this find the largest number and subtract the smallest number from it. Temperature it makes sense to label the & FH If you're asked to draw a line (or curve) of y-axis up to 25 cm/s. cs best fit, draw a line through or as near to = as many points as possible, ignoring any S anomalous results. Don't join the crosses up The dependent variable = 10 ~ao goes on the y-axis L's (the vertical one). 2 anomalous result Draw tt nice and big (covering at a8 least half of the graph paper) 0 : ; The independent variable goes on 0 5 10 15 20 25 30 the x-axis (the horizontal one). ——---en > Temperature (°C) penne Remember to include the units. NE / R CTY Fp ou can use this method to calculate any rate s from a graph 1) The gradient (slope) of a graph tells you how change in y not just the rate Just remember tha of a ae / quickly the dependent variable changes if you gradient = s much something t a rate is how changes over change the independent variable. —— => change in x iytime, MUTT \ so x needs to be t}ne time. = PITTA yay ANYBP YA | rt yp ys This graph shows the volume of gas produced in a reaction against time. The graph is linear (it's a straight line graph), so you can simply calculate the gradient of the line to find out the rate of reaction. 1) To calculate the gradient, pick two points on the line EZ hatiae if font that are easy to read and a good distance apart. (cm’) of Volume gas 2) Draw _a line down from one of the points and a line across from the Time (s) other to make a triangle. The line drawn down the side of the triangle A ' i ~as a; a aw ELS : youve got a cur Us S ved graph, you can - is the change in y and the line across the bottom is the change in x. E hei tyrate at any point by dra wing a Change in y = 6.8 - 2.0 = 4.8 om? Change in x = 5.2-. change in 8 cm? 1.6 = 8.6 6 === 7" the gradient 2 ofstiaht line that touches on a curve. You can = then f d = the tangent in the Rate = gradient = chaneo 1.3 cm%/s or LB om@st = way, to give : : fuel = geinx 3.6s_ enn ENSURWAWOU REasEcm’s"'. The units of the gradient are (units of y)/(units of x). cm?/s can also be written CE BERT SEWER TTTa 2) The intercept of a graph is where the line of best fit crosses one of the axes. The x-intercept is where the line of best fit crosses the x-axis and the y-intercept is where it crosses the y-axis. 1) You can get three types of correlation (relationship) between variables: —= =p, 2) Just because there's correlation, it doesn't mean the change in one ra variable is causing the change in POSITIVE correlation: INVERSE (negative) correlation: |correlation: NO the other — there might be as one variable increases as one variable increases no relationship between other factors involved (see page 9). the other increases. the other decreases. the two variables. I love eating apples — I call it core elation... Science is all about finding relationships between things. And I don’t mean that chemists gather together in corners to discuss whether or not Devini and Sebastian might be a couple... though they probably do that too. Working Scientifically  haba and maths skills are all very well, but the numbers don't mean er ifyou can't4 get— unitsedhe "SI Units Are Used All Round the World _ 1) It woolen t be all that meet if | defined volume in ean of bath tubs, you defined it in terms of egg-cups and my pal Sarwat defined it in Quantity S| Base Unit terms of balloons — we'd never be able to compare our data. 2) To stop this happening, scientists have come up with a set of standard units, called SI units, that all scientists use to measure second, s their data. Here are some SI units you'll see in Biology: a S anti aeetae come in a Race aiesetesizes. irae eaare te alune. = the effect of these errors by repeating the would 7 change. You can “4 reduce WTI iaidy. potato 12 - experiment and calculating a mean percentage change at each concentration. = 1111) 1), ;,,, r cain i And to all you cold-hearted potato murderers... Just remember, osmosis is really just a fancy word for the diffusion of water molecules. It’s simple really. Ql Explain what will happen to the mass of a piece of potato added to a concentrated salt solution. [2 marks] Topic 1 — Cell Biology  Sometimes substances need to be absorbed against a concentration gradient, i.e. from a lower to a higher concentration. This process is lovingly referred to as ACTIVE TRANSPORT. Rockne 1) As you saw on page 4, the cells on plant roots grow into "hairs" which stick out into the soil. 2) Each branch of a root will be covered in millions of these microscopic hairs. 3) This gives the plant a large surface area for absorbing water and mineral ions from the soil. 4) Plants need these mineral ions for healthy growth. 5) The concentration of minerals is usually higher in the root hair cells than in the soil around them. 6) So the root hair cells can't use diffusion to take up minerals from the soil. SOPRA hy | Root Hairs Take in Minerals Using Active Transport — "Vater js taken ‘es L ~ Into root hair cells by osmosis 1) Minerals should move out of the root hairs if they followed the rules of diffusion. ee Page 21) The cells must use another method to draw them in. LIA DEDj AVE yyy 2) That method is, in fact, a conveniently mysterious process called “active transport”. 3) Active transport allows the plant to absorb minerals from a very dilute solution, against a concentration gradient. This is essential for its growth. But active transport needs ENERGY from respiration to make it work. 4) Active transport also happens in humans, for example in taking glucose from the gut (see below), and from the kidney tubules. a — ; ; Ci >) ee ae eee We Need Active Transport to Stop Us Starving — Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood. 1) When there's a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood. 2) BUT — sometimes there's a lower concentration Inside of nutrients in the gut than there is in the blood. the 3) This means that the concentration gradient is the wrong way. 4) The same process used in plant roots is used here...... Active transport”. 5— Active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way. 6 See This means that glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. I can then be transported to cells, where it's used for respiration (see p.61). Active transport — get on yer bike... An important difference between active transport and diffusion is that active transport uses energy. Imagine a pen of sheep in a field. If you open the pen, the sheep will happily diffuse from the area of higher sheep concentration into the field, which has a lower sheep concentration — you won’t have to do a thing. To get them back in the pen though, you'll have to put in quite a bit of energy. Ql What is the purpose of active transport in the gut? [1 mark] Topic 1 — Cell Biology  1) Cells can use diffusion to take in substances they need and get rid of waste products. For example: * Oxugen and carbon dioxide are transferred between cells and the environment during gas exchange. ¢ In humans, urea (a waste product produced from the breakdown of proteins, see p.75) diffuses from cells into the blood plasma for removal from the body by the kidneys. 2) How easy it is for an organism to exchange substances with its environment depends on the organism's surface area to volume ratio (SA : V). saidtich ed a = A ratio shows how big one value is compared to another. The larger an organism is, the smaller its surface area is compared to its volume. You can show this by calculating surface area to volume ratios: A hippo can be represented by a 2 cm X 4 cm X 4 em block. The area of a surface is found by the equation: LENGTH x WIDTH So the hippo's total surface area is: (4 x 4) x 2 (top and bottom surfaces of block) + (4 x 2) x 4 (four sides of the block) = 64 cm’. The volume of a block is found by the equation: LENGTH x WIDTH x HEIGHT So the hippo's volume is 4 x 4 x 2 = 32 cm’. The surface area to volume ratio of the hippo can be written as 64 : 32. The cube mouse's To simplify the ratio, divide both sides of the ratio by the volume. surface area is six times So the surface area to volume ratio of the hippo is 2 : I. its volume, but the cube hippo's surface area A mouse can be represented by a 1 cm X 1 cm X 1 cm block. is only twice its volume. lcm Its surface area is (1 X 1) X 6 = 6 cm’. Sag, |ema So the mouse has a Its volume is 1 X 1 X 1 = 1 cm. lcm 33 larger surface area So the surface area to volume ratio of the mouse is 6 : 1. AA compared to its volume. 1) In single-celled organisms, gases and dissolved substances can diffuse directly into (or out of) the cell across the cell membrane. It's because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell. 2) Multicellular organisms have a smaller surface area compared to their volume — not enough substances can diffuse from their outside surface to supply their entire volume. This means they need some sort of exchange surface for efficient diffusion (see pages 24-25 for some examples). The exchange surface structures have to allow enough of the necessary substances to pass through. 3) Exchange surfaces are ADAPTED to maximise effectiveness: * They have a thin membrane, so substances only have a short distance to diffuse. * They have a large surface area so lots of a substance can diffuse at once. * Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly. * Gas exchange surfaces in animals (e.g. alveoli) are often ventilated too — air moves in and out. Not that I’m endorsing putting animals in boxes... A large surface area is a key way that organisms’ exchange surfaces are made more effective. Ql A bacterial cell can be represented by a 2 tum x 2 um * | ym block. Calculate the cell’s surface area to volume ratio. [3 marks] Topic 1 — Cell Biology  24 This page is about how two different parts of the human body are adapted so that substances can diffuse through them most effectively. The first bit is about how gases in the lungs get into and out of the blood. The second is about how digested food gets from the gut to the blood. ill 1) The job of the lungs is to transfer oxygen to the Psa blood and to remove waste carbon dioxide from it. 2) To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place. Blue = blood with carbon dioxide. Red = blood with oxygen. 3) The alveoli are specialised to maximise the diffusion of O, and CO,. They have: e An enormous surface area (about 75 m? in humans). ¢ A moist lining for dissolving gases. blood capillary ¢ Very thin walls. * A good blood supply. 1) The inside of the small intestine is covered in millions and millions of these tiny little projections called villi. 2) They increase the surface area in a big way so that digested food is absorbed much more quickly into the blood. 3) Notice they have: * a single layer of surface cells, Nexto DOVAD ge A AI Saas r * avery good blood supply to assist quick absorption. RUE URL = The digested food moves into = = the blood by diffusion and by = longitudinal = active transport (see page 22). = muscle © ZA ACUTEace Al Veoli — the Italian gas man... Thankfully, our bodies are well adapted for efficient diffusion of substances. But the array of life’s snazzy exchange surfaces doesn’t stop here, oh no — just take a look at what’s coming up on the next page... Ql Give one way in which alveoli are adapted for gas exchange. [1 mark] Q2 Describe how the surface area of the small intestine is maximised for absorption. [1 mark] Topic 1 — Cell Biology  1) Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens. The leaf's structure is adapted so that this can happen easily. 2) The underneath of the leaf is an exchange surface. It's covered in biddy little holes called stomata which the carbon dioxide diffuses in through. 3) Oxugen (produced in photosynthesis) and water vapour also diffuse out through the stomata. (Water vapour is actually lost from all over the leaf surface, but most of it is lost through the stomata.) 4) The size of the stomata are controlled by guard cells — ff SO see page 44. These close the stomata if the plant is CO diffucssinio leat | losing water faster than it is being replaced by the roots. | Oxygen and water vapour si Without these guard cells the plant would soon wilt. siffusp nett ofthe Jeat 5) The flattened shape of the leaf increases the area of this exchange surface so that it's more effective. 6) The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the area of this surface so there's more chance for carbon dioxide to get into the cells. The water vapour evaporates from the cells inside the leaf. Then it escapes by diffusion because there's a lot of it inside the leaf and less of it in the air outside. The gills are aygas Bias ry in fish ich. Water (containing oxygen) enters the fish through its mouth and passes out through the gills. As this happens, Water oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water. Each gill is made of lots of thin plates called gill filaments, which give a big surface area for exchange of gases. ep ‘gill| Patan The gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more. The lamellae have lots of blood capillaries to speed up diffusion. arteries’ They also have a thin surface layer of cells to minimise the | distance that the gases have to diffuse. gill filaments 7) Blood flows through the lamellae in one direction and water flows over in the opposite direction. This maintains a large concentration gradient between the water and the blood. 8) The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood. In, out, in, out, shake that oxygen about... There’s a theme here — multicellular organisms are really well adapted for getting the substances they need to their cells. It makes sense — if they couldn’t do this well, they’d die out. If you’re asked in an exam how something’s adapted for exchange, think about whether surface area is important — cos it often is. Ql Give two ways in which the structure of a gill is adapted for effectivegas g eippiates a ica, Topic 1 — Cell Biniaal  Well, that's Topic 1 done and dusted. Now there's only one way to find out whether you've learnt anything from it. And you know what that is, I'll bet. It's obvious... 1 mean, there's a whole load of questions staring you in the face — chances are, it's got to involve those in some way. And sure enough, it does. * Try these questions and tick off each one when you get it right. * When you've done all the questions under a heading and are completely happy with it, tick it off. Cells and Microscopy (p.11-13) [_| 1) Name five subcellular structures that both plant and animal cells have. 2) What three things do plant cells have that animal cells don't? 3) Where is the genetic material found in: a) animal cells, b) bacterial cells? 4) What type of organisms are bacteria — prokaryotes or eukaryotes? 5) Which gives a higher resolution — a light microscope or an electron microscope? Differentiation and Division (p.14-16) [Y 6) What is cell differentiation? 7) Give three ways that a sperm cell is adapted for swimming to an egg cell. 8) Draw a diagram of a nerve cell. Why is it this shape? 9) What are chromosomes? 10) What is the cell cycle? 11) What is mitosis used for by multicellular organisms? 12) What is the name of the process by which bacteria divide? OAS SN AN Culturing Microorganisms (p.17-18) |_| 13) a) What is the maximum temperature that microorganisms should be grown at in a school lab? b) Why shouldn't a temperature above this be used? 14) There are ways in which you can make sure an experiment testing the effect of antibiotics on bacteria has not been contaminated. Give three of these ways. Stem Cells (p.19) [. | 15) Give two ways that embryonic stem cells could be used to cure diseases. 16) Why might some people be opposed to the use of human embryos in stem cell research? Exchanging Substances (p.20-25) a 17) What is diffusion? 18) Name three substances that can diffuse through cell membranes, and two that can't. 19) What type of molecules move by osmosis? 20) Give the two main differences between active transport and diffusion. 21) Give three adaptations of exchange surfaces that increase the efficiency of diffusion. 22) Give two ways that the villi in the small intestine are adapted for absorbing digested food. 23) Explain how leaves are adapted to maximise the amount of carbon dioxide that gets to their cells. SQ] BS] ot] SS S| GS FS BS S| ES Topic 1 — Cell Biology  Topic 2 — Organisation Some organisms contain loads of cells, but how, you might wonder, do all these cells end up making a pecalng human or sola the answer's organisation. Without it, they'd just make a meaty splodge. fultic ellular ar Organisms aare Made ‘Up of Organ Systems 1) Cells aretheRivet iting til that make upall living organisms. 2) As you know from page 14, specialised cells carry out a particular function. 3) The process by which cells become specialised for a particular job is called differentiation. Differentiation occurs during the development of a multicellular organism. 4) These specialised cells form tissues, which form organs, which form organ sustems (see below). 5) Iticellular isms (e.g. squirrels) have different systems inside them eae for Sea and transporting materials. Epithelial cell less than 0.1 mm A tissue is a group gph sirallan cells that work fdpethat to carry out a particular function. It can include more than one type of cell. In mammals (like humans), examples of tissues include: Epithelial ticcue Epithelial tissue 1) Muscular tissue, which contracts (shortens) to move whatever it's attached to. 2) Glandular tissue, which makes and secretes chemicals like enzymes and hormones. 3) Epithelial tissue, which covers some parts of the body, e.g. the inside of the gut. An organ is a group of different tissues that work together to perform a certain function. For example, the stomach is an organ made of these tissues: Stomach 1) Muscular tissue, which moves the stomach wall to churn up the food. 2) Glandular tissue, which makes digestive juices to digest food. 3) Epithelial tissue, which covers the outside and inside of the stomach. a (over 1000 times longer than an An oisn stom |is afarour of organss working together Salivary glands epithelial cell) to perform a particular function. : Liver For example, the eee tie (found in humans and other mammals) Digestive breaks down and absorbs food. It's made up of these organs: system 1) Glands (e.g. the pancreas and salivary glands), Stomach which produce digestive juices. 2) The stomach and small intestine, which digest food. Pancreas 3) The liver, which produces bile. Small intestine | 4) The small intestine, which absorbs soluble food molecules. Large intestine 5) The large intestine, which absorbs water from undigested food, AC) OR OG TaSr I You need to know where leaving faeces. these organs are on a = Organ systems work ipeshe to make entire organisms. IEEE, diagram — see page 31 too. = ey ve eeereray Velev ————E—Ee | Soft and quilted — the best kind of tissues... So in summary, an organism consists of organ systems, which are groups of organs, which are made of tissues, which are groups of cells working together. Now just for the thrill of it, here’s a practice question. Ql The bladder is an organ. Explain what this means. [2 marks] Topic 2 — Organisation  1) Living things have thousands of different chemical reactions going on inside them all the time. These reactions need to be carefully controlled — to get the right amounts of substances. 2) You can usually make a reaction happen more quickly by raising the temperature. This would speed up the useful reactions but also the unwanted ones too... not good. There's also a limit to how far you can raise the temperature inside a living creature before its cells start getting damaged. 3) So... living things produce enzymes that act as biological catalysts. Enzymes reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body. A CATALYST is a substance which INCREASES the speed of a reaction, without being CHANGED or USED UP in the reaction. 4) Enzymes are all large proteins and all proteins are made up of chains of amino acids. These chains are folded into unique shapes, which enzymes need to do their jobs (see below). Enzymes Have Special Shapes So They Can Catalyse Reactions 1) Chemical reactions usually involve things either being split apart or joined together. 2) Every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction. 3) Enzymes are really picky — they usually only catalyse one specific reaction. SMU tay, = The substance that 4) This is because, for the enzyme to work, the substrate has to fit into its an enzyme acts on is active site. If the substrate doesn't match the enzyme's active site, then z,, called the substrate. Labit ee the reaction won't be catalysed. COLE MUIR Nsitay vate 5) This diagram shows the ‘lock and keu' model of enzyme action. This is simpler than how enzymes actually work. In reality, the active site changes shape a little as the substrate binds to it 2s to get a tighter fit. This is called the enfyme ‘induced fit' model of enzyme action. Enzymes Need the Right Temperature and pH : This is the optimum temp, 1) Changing the temperature changes the rate of an enzyme-catalysed reaction. S| — where the enzyme is : : : : £ \ymost active 2) Like with any reaction, a higher temperature increases the rate at first. S But if it gets too hot, some of the bonds holding the enzyme together 6 break. This changes the shape of the enzyme's active site, so the substrate o won't fit any more. The enzyme is said to be denatured. 0 °C 45°C Temp, 3) All enzymes have an optimum temperature that they work best at. 4) The pH also affects enzymes. If it's too high or too low, : ; ‘ Rate.or Optimum the pH interferes with the bonds holding the enzyme together. ssl pH This changes the shape of the active site and denatures the enzyme. 5) All enzymes have an optimum pH that they work best at. It's often neutral pH 7, but not always — e.g. pepsin is an enzyme used to break down proteins pH in the stomach. It works best at pH 2, which means it's well-suited to the acidic conditions there. If only enzymes could speed up revision... Make sure you use the special terms like ‘active site’ and ‘denatured’ — the examiners will love it. Ql Explain why enzymes have an optimum pH. [2 marks] Topic 2 — Organisation  The enzyme amylase catalyses the breakdown of starch to maltose. It's easy to detect starch using iodine solution — if starch is present, the iodine solution will change from browny-orange SUS iU se to blue-black. This is how you can investigate how pH affects amulase activity: You could use an lectiee water bath, instea d of 1) Put a drop of iodine solution into every well of a spotting tile. a Bunsen and a beaker 2) Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the of water. to contro l the Bunsen burner. Put a beaker of water on top of the tripod and heat the water By Aarer Sp eeabire BLE YTV Ada yyy until it is 35 °C (use a thermometer to measure paced CEL La a the temperature). Try to keep the temperature of mixture sampled the water constant throughout the experiment. Apis every 30 seconds 3) Use a syringe to add I cm? of amylase solution serene a eect and 1 cm? of a buffer solution with a pH of 5 to a bufer f 3 pipette boiling tube. Using test tube holders, put the tube — lution : drop of iodine into the beaker of water and wait for five minutes. "7 _ solution 4) Next, use a different suringe to add 5 cm? te eee bi of a starch solution to the boiling tube. 5) Immediately mix the contents of the boiling tube and start a stop clock. 6) Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains browny-orange, starch is no longer present. 7) Repeat the whole experiment with buffer solutions of different pH values SY iii yyy, G to see how pH affects the time taken for the starch to be broken down. toouaccould use a curately Me pH meter = asure the 8) Remember to control any variables each time (e.g. concentration Nay PH ofyour sol utions, AMTP and volume of amylase solution) to make it a fair test. OST. 1) It's often useful to calculate the rate of reaction after an experiment. Rate is a measure of how much something changes over time. 2) For the experiment above, you can calculate the rate of reaction using this formula:7 VATE EV Ly \ E.g. = The units are =. At pH 6, the time taken for amylase to break down all of the starch in a solution | = ins‘ since = was 90 seconds. So the rate of the reaction = 1000 = 90 = Ils" (2 s.f.) = fate is given = = per unit time. = ALIN ODA PMNS 3) If an experiment measures how much something changes over time, you calculate the rate of reaction by dividing the amount that it has changed by the time taken. FEXAANPLE:) The enzyme catalase catalyses the breakdown of hydrogen peroxide into water and oxygen. During an investigation into the activity of catalase, 24 cm’ of oxygen was released in 5O seconds (s). Calculate the rate of the reaction. Write your answer in cm?/s. Amount of product formed = change = 24 cm? Rate of reaction = change + time = 24 cm? + 50 s = 0.48 cm?/s Mad scientists — they’re experi-mental... You could easily adapt this experiment to investigate how factors other than pH affect the rate of amylase activity. For example, you could use a water bath set to different temperatures to investigate the effect of temperature. Ql An enzyme-controlled reaction was carried out at pH 4. After 60 seconds, 33 cm’ of product had been released. Calculate the rate of reaction in cm’/s. [1 mark] Topic 2 — Organisation  30 Enzymes and Digestion —_ The enzymes used in digestion are produced by cells and then released into the gut to mix with fo od. Digestive Enzymes Break Down Big Molecules 1) Starch, proteins and fats are BIG molecules. They're too big to pass through the walls of the digestive system, so digestive enzymes break these BIG molecules down into smaller ones like sugars (e.g. glucose and maltose), amino acids, glycerol and fatty acids. These smaller, soluble molecules can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream. | Carbohydrases Convert Carbohydrates into Simple Sugars. It breaks down starch. oe aa TL Amylase ig an example of a carbohydrase Starch is a carbohydrate. LIVI to i Starch ‘Amylase | Ay 7 77 Ss Maltose venzyme > ry) and other sugars, e.g. dextrins | Amylase is made in three places: 1) The salivary glands 2) The pancreas 3) The small intestine |Proteases Convert Proteins into Amino Acids | ee | : |Proteins| Protease ee enzymes Z\ZRY Amino acids Proteases are made in three places: 1) The stomach (it's called pepsin there) 2) The pancreas 3) The small intestine Lipases Convert Lipids into Glycerol and Fatty Acids j Z WEEE yy Lipid tt Fost See = Remember, I —,- oe 208 = lipids are fats CLE ‘Glycerol & fatty acids| _, EeRUaWen) Lipases are made in two places: 1) The pancreas 2) The small intestine 2) The body makes good use of the products of digestion. They can be used to make new carbohydrates, proteins and lipids. Some of the glucose (a carbohydrate) that's made is used in respiration (see p.61). Bile Neutralises the Stomach Acid and Emulsifies Fats| 1) Bile is produced in the liver. It's stored in the gall bladder before it's released into the small intestine. 2) The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline — it neutralises the acid and makes conditions alkaline. The enzymes in the small intestine work best in these alkaline conditions. 3) It emulsifies fats. In other words it breaks the fat into tiny droplets. This gives a much bigger surface area of fat for the enzyme lipase to work on — which makes its digestion faster. What do you call an acid that’s eaten all the pies... Make sure you know the examples of amylase, protease and lipase, and the reactions that they catalyse. Ql Bile is a product of the liver. Describe and explain its role in digestion. [4 marks] Topic 2 — Organisation  ndDigestion —__ So now you know what the enzymes do, here's a nice big picture of the whole of the digestive system. It pummels the food with its muscular walls. 2) \t produces the protease enzyme, pepsin. 3) It produces hydrochloric acid Where ~~ for two reasons: is produced. a) To kill bacteria Bile neutralises b) To give the right pH for the stomach acid and protease enzyme to work emulsifies fats. (pH 2 — acidic). CoS " Ga! ie ee f al | > Q yer Where bile is stored, Produces protease, amulase before it's released and lipase enzymes. It releases these into the small intestine. into the small intestine. rz » ‘ Ss vise “5 Syetalet a ; 3 — 1) Produces protease, amylase Where excess water and lipase enzymes to is absorbed from complete digestion. the food. 2) This is also where the digested food is absorbed out of the digestive system into the blood. Where the faeces (made up mainly of indigestible food) are stored before they bid you a fond farewell through the anus. Mmmm — so who’s for a chocolate digestive... Did you know that the whole of your digestive system is actually a hole that goes right through your body. Think about it. It just gets loads of food, digestive juices and enzymes piled into it. Most ofit’s then absorbed | into the body and the rest is politely stored for removal. Ql Name the three parts of the digestive system that produce protease enzymes. [3 marks] Topic 2 — Organisation  There are some clever ways to identify what type of food molecule a sample contains. For each of the tests, you need to prepare a food sample. It's the same each time though — here's what you'd do: 1) Get a piece of food and break it up using a pestle and mortar. 2) Transfer the ground up food to a beaker and add some distilled water. 3) Give the mixture a good stir with a glass rod to dissolve some of the food. 4) Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food. Gugare are feundiin all sorts offoods such as biscuits, cereal and bread. There are two types of sugars — non-reducing and reducing. You can test for reducing sugars in foods using the Benedict's test: 1) Prepare a food sample and transfer 5 cm® to a test tube. 2) Prepare a water bath so that it's set to °C. 75 3) Add some Benedict's solution to the test tube (about 10 drops) using a pipette. 4) Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes. Make sure the tube is pointing away from you. 5) If the food sample contains a reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow or brick-red — it depends on how much sugar is in the food. You can also check food samples for the presence of starch.