CCEA GCSE Biology - Hodder Education

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WORKBOOK ANSWERSCCEA GCSE BiologyUnit 1: Cells, living processes and biodiversityUnit 2: Body systems, genetics, microorganisms and healthThis Answers document provides suggestions for some of the possible answers that might be given for the questions asked in the Workbook. They are not exhaustive and other answers may be acceptable, but they are intended as a guide to give teachers and students feedback.Exam-style question (QWC) answersSome of the exam-style questions assess quality of written communication (QWC) and have what are referred to as banded mark schemes. The ‘bands’ are linked to the marking of ‘indicative points’ which show the content that examiners will be looking for. The number of indicative points in your answer will determine the band to which it will be allocated. QWC then determines the actual mark awarded within that band. The table below shows a typical banded mark scheme and how the 6 marks in a QWC question would be allocated. BandResponse MarksAThe candidate selects at least X (number X is dependent on the question) of the indicative points.The relevant material is organised with a high degree of clarity and coherence.There is widespread and accurate use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently high standard to make the meaning clear.5–6BThe candidate selects at least Y (number Y is lower than X but dependent on the individual question) of the indicative points.The relevant material is organised with some degree of clarity and coherence.There is some use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently competent standard to make the meaning clear. 3–4CThe candidate selects at least Z (number Z is lower than Y but dependent on the individual question) of the indicative points.The organisation may lack clarity and coherence.There is little use of specialist vocabulary.Presentation, spelling, punctuation and grammar may be such that the meaning is not clear. 1–2DResponse not worthy of credit.0Unit 1: Cells, living processes and biodiversityCellsCells and microscopy1aiPlasmid [1]iiCell membrane/cytoplasm [1]iiiAny two from:Plant and animal cells do not have plasmids.Plant and animal cells have a nucleus/nuclear membrane.Plant and animal cells have mitochondria. [2]bElectron microscopes have a greater resolution [1], allowing us to see structures we were previously not aware of/see the internal cell structures in greater detail. [1][6 marks]2aUnitSymbolNumber per metre in standard formMillimetre [1]mm [1]1 × 103Micrometreμm1 × 106 [1]bCell measured as 5 cm [1]= 50 000 μm [1]50 000/5 = 10 000 [1](Magnification = ×10 000)It is very important that you show your working when told to do so in a question. If you make a mistake, and you do not show your working, you will get no marks even if the mistake is in the final stage of the calculation.[6 marks]Stem cells, cell specialisation and diffusion3aA cell that can divide and produce different types of cell. [1]bIn meristems at the tips/apices [1] of both shoots and roots. [1][3 marks]4aLevel of organisationDescriptionTissue [1]Group of similar cells with same general structure and functionOrgan systemOrgans are organised into organ systems, with each organ having a function relating to the overall function of the system [1]Organ [1]Structure made of several types of tissue that carries out a particular functionbiIt decreases [1]iiAs size increases, the surface area across which substances can diffuse decreases proportionally. [1] Eventually, there is not enough body surface across which gases can diffuse. [1] Specialised gas exchange surfaces increase the area across which the gases can diffuse (to compensate). [1][7 marks]Exam-style questions1aSite of cell respiration/release energy [1]bThere is a greater concentration of carbon dioxide inside the cell than outside. [1] This is due to the cell respiring (and producing carbon dioxide). [1]cCytoplasm [1]; cell membrane [1]dHigher temperature [1]; higher concentration gradient [1]The question asks for factors that will increase the rate of diffusion. Therefore, 'higher temperature' would get a mark but 'temperature' would not.[7 marks]2aiPeople with leukaemia often have a shortage of certain blood types. [1] This is due to the disease/pre-treatment damaging the bone marrow that produces these cells. [1]iiAll the types of blood cell [1]iiiBone marrow/blood [1]ivTo prevent the body’s immune system attacking the donated cells/to prevent rejection [1]bEmbryonic stem cells can produce a wide range of cell types/any of the types of cell found in the body. [1] (Adult) stem cells/the cells used to treat leukaemia can only produce blood cells. [1]c45 mm = 45 000 ?m [1]45 000/600 [1]= 75 ?m [1][10 marks]Photosynthesis and plantsPhotosynthesis1aicarbon dioxide + water [1] → glucose + oxygen [1]ii6CO2 + 6H2O [1] C6H12O6 [1] + 6O2bPhotosynthesis is a process that takes place only in the presence of light [1] energy [1].[6 marks]2aLeaves are destarched to ensure that they contain no starch at the beginning of the investigation. [1] This ensures that any starch present when carrying out the starch test was produced during the investigation only. [1]You would not be awarded for stating that destarching a leaf removes any starch present — this is implied in the questionbEthanol [1]; iodine [1][4 marks]3aVariegated leaves have chlorophyll present in parts of the leaf only. [1]bOnly part of the leaf is involved in photosynthesis/photosynthesis is less efficient. [1][2 marks]4aiRespiration [1]iiCarbon dioxide [1]iiiChloroplasts [1]You would not be rewarded for answering chlorophyll here. A chloroplast is a structure; chlorophyll is a chemical (found within the chloroplast).bi5 arbitrary units [1]iiTemperature [1]; carbon dioxide [1][6 marks]Leaf structure5aiThe stomata (pores) allow gases to enter and leave the leaf. [1] The guard cells control the opening and closing of the stomata. [1]iiAny two from:It avoids rainwater entering the leaf via the stomata.The intercellular spaces are close to the lower surface (allowing a continuous flow of gases from the atmosphere to and from the cells inside the leaf).It allows the cells in the palisade layer to be packed tightly to carry out photosynthesis (without the need to have intercellular spaces among them to facilitate gas exchange). [2]bThe intercellular spaces allow gases to diffuse between the mesophyll cells and the stomata (and atmosphere). [1] This allows carbon dioxide to enter the leaf for photosynthesis/oxygen to enter for respiration/oxygen to diffuse out from photosynthesising cells/carbon dioxide to diffuse out from respiring cells. [1][6 marks]Exam-style questions1aSodium hydroxide [1]bDestarch a potted plant. [1]Securely attach a beaker/container containing sodium hydroxide to a leaf. [1]Securely attach a beaker/container containing water to another leaf as a control. [1]Leave in bright light for 5–48 hours. [1]Carry out a starch test on both leaves. [1] (The leaf with the sodium hydroxide will show no starch present and the leaf with water will show the presence of starch.)It is important to set up a control with a beaker/container containing water to show that it is the absence of carbon dioxide that prevents starch being formed. If a control was not used, it would be impossible to show that it was the absence of carbon dioxide that was responsible rather than another reason, for example the leaf being damaged when it was being placed into the beaker/container.[6 marks]2aThe compensation point is reached when respiration and photosynthesis are taking place at the same rate. [1]biSet up apparatus containing pondweed in bicarbonate indicator in a sealed boiling tube (sealed using a bung). [1]Leave in light for a set period of time (e.g. 30 minutes). [1]Repeat with a different light intensity through changing distance of lamp/or through using a lamp with a dimmer switch. [1]The compensation point is achieved when the pondweed is in a light intensity that produces no colour change in the bicarbonate indicator (i.e. the indicator remains red after the 30 minutes). [1]The question asks how you could carry out an investigation, so marks are awarded for you explaining how to do it rather than showing you understand why each stage is done.iiAny two from:Same pondweedSame temperatureLeave for same amount of timeSame lamp (if changing distance of lamp from pondweed)Same distance of lamp from pondweed (if using a dimmer switch) [2][7 marks]3aiTransparent [1]; waterproof [1]iiAny three from:Close to the upper leaf surface (where there is more light)Each cell has many chloroplastsEnd-on to leaf surfaceSo tightly packed (allowing many photosynthesising cells to be close to the upper surface) [3]iiiA — upper epidermis; B — palisade mesophyll; C — spongy mesophyll [2]All three correct = 2 marks; one or two correct = 1 markbNo photosynthesis in layer A; high rate in layer B and a reduced/variable rate in layer C. [1]No photosynthesis in the upper epidermis/layer A as the cells do not contain chloroplasts. [1]High rate of photosynthesis in the palisade mesophyll/layer B as these cells contain many chloroplasts/are packed tightly together. [1]Lower rate of photosynthesis in the spongy mesophyll as the cells contain fewer chloroplasts/are less tightly packed due to the presence of air spaces. [1][11 marks]Nutrition and food testsBiological molecules1aGlucose — lactose — glycogen [1]biAmino acid [1]iiEnzyme/antibody/any other appropriate example [1]ciGlycerol and fatty acids [1]iiSource of energy/energy storage [1][5 marks]2Food testedReagentInitial colourFinal colourHeating required?FatEthanolColourlessWhite emulsionNoReducing sugarBenedict’sBlueBrick-red precipitateNoStarchIodine solutionYellow-brownBlue-blackNo1 mark for each correct row[3 marks]Exam-style questions1aBiuret [1]bProteins can be formed from different numbers of amino acids. [1] The sequence of amino acids (the way in which amino acids are linked together) in each protein can be different. [1]Even if you did not know that there are only 20 amino acids, or that amino acids are linked together in different ways to form proteins, you should be able to use the information provided to deduce that these could be different in each protein.[3 marks]2a(24/16) × 100 [1]= 150% [1]buse the same mass of each food [1]use the same volume of water [1]keep the burning food the same distance below the boiling tube [1]cThe two pieces of bacon had different proportions of fat and protein/one piece had more fat (or protein) than the other. [1][6 marks]Enzymes and digestionEnzymes1aProteins [1]bActive site [1]; lock and key [1]; specificity [1][4 marks]2EnzymeSubstrateProducts(s)Carbohydrase/amylase [1]StarchSugarProteaseProteinAmino acids [1]LipaseLipids (fats)Glycerol and fatty acids [1][3 marks]3aOptimum [1]bPosition on graphRate of enzyme activityExplanationWLowReduced rates of collision between the enzyme and the substrate, [1] due to reduced (kinetic) energy. [1]YModerateSmall amounts of denaturation (of the active site), [1] as the enzyme is slightly above the optimum temperature. [1]ZVery lowThe active site has become progressively denatured (as the temperature is well above the optimum). [1][6 marks]Digestion and absorption4Good blood supply [1]; thin and permeable membranes [1][2 marks]Exam-style questions1aAs enzyme concentration increases, the rate of reaction increases. [1] It then levels off. [1] The increase is due to more active sites being available (as there are more enzymes). [1] At higher enzyme concentrations, there are not enough substrate molecules (the enzymes are in excess/it is the number of substrate molecules that is limiting. [1]biAn enzyme inhibitor can fit the active site, blocking the substrate from joining. [1]iiAs more inhibitor is added, enzyme activity (rate of reaction) will decrease [1] because more enzyme active sites will be blocked. [1] Therefore, fewer enzymes will be available to react. [1][8 marks]2aiVillus [1]iiLacteal [1] (central structure that branches off) and capillary network [1] (vessels surrounding the lacteal) correctly labellediiiIt absorbs fatty acids and glycerol/the breakdown products of fats/lipids. [1]ivIt is a single layer of surface (epithelial) cells. [1] This reduces the distance/ number of cell layers that absorbed food molecules diffuse through. [1]vIts long length [1]; the presence of folds [1]bReduced absorption [1] because of the reduced surface area [1][10 marks]The respiratory system, breathing and respirationThe respiratory system and lung model1aStructureFunctionAlveoliRespiratory surface/increase surface area for the exchange of gases [1]Bronchioles [1]The structures that link alveoli to the bronchiIntercostal musclesContract, pulling the ribs up and out [1]Pleural fluidReduces friction during breathing [1]b4 — 2 — 1 — 3 [1][5 marks]2Any three from:a large surface areathin exchange surfacesmoist wallspermeable wallsa diffusion gradient'Good blood supply' would not get awarded here, as there is no blood system in plants.[3 marks]Respiration3aglucose + oxygen [1] → energy + carbon dioxide + water [1]bFeatureType of respirationAerobicAnaerobicOxygen usedYes/NoYes/NoCarbon dioxide producedYes/NoYes/NoLactic acid producedYes/NoYes/NoAmount of energy producedHigh/LowHigh/Low1 mark for each correct rowcAnaerobic respiration in yeast produces alcohol/carbon dioxide/does not produce lactic acid (or converse). [1][6 marks]Exam-style questions1aiThe rubber sheet is pulled down. [1] The volume inside the bell jar increases, causing the pressure to decrease. [1] Air enters the balloons (from the atmosphere), causing the balloons to inflate. [1]iiInhalation/breathing in/inspiration [1]bAny two from:The sides of the bell jar do not move up and out.The relative size of the thoracic cavity is much smaller in humans.In humans (at the start of inhalation) the diaphragm is a domed shape (rather than flattened). At the end of inhalation it is flattened (rather than pulled downwards) (or converse). [2]ci250 – 150 [1]= 100 arbitrary units [1]iiRate of breathing increased [1]iiiDuring exercise, more oxygen is needed [1] for more respiration [1]; to release more energy (for increased muscle contraction). [1][12 marks]2aAnaerobic respiration [1]bGlucose supply was running out, [1] causing a reduction in the rate of anaerobic respiration so that ethanol production levels off. [1]cTemperature increase/increase in carbon dioxide concentration [1][4 marks]The nervous system and hormonesThe eye1aCornea [1]; lens [1]bIris [1]cThe ciliary muscles relax. [1] Suspensory ligaments are stretched. [1] The lens is pulled and becomes thinner. [1][6 marks]Neurones and synapses2aMyelin sheath (the string of structures surrounding the long axon) correctly labelled [1]bAny two from:branched endslong axon lengthproduces transmitter chemical at tips [2]cTip/end of branch at end of neurone circled [1][4 marks]Voluntary and reflex actions3aiVoluntary [1]; quicker/faster [1]iiBlinking/withdrawal of hand from hot object/any other appropriate example [1]bD — C — E — B — A [2]All correct = 2 marks; any two in sequence = 1 mark[5 marks]Hormones and diabetes4aA chemical messenger produced by glands that travels in the blood to a target organ, where it acts. [1]biPancreas [1]iiIncrease in blood glucose concentration/meal rich in sugar/carbohydrate [1]iiiThe liver absorbs more glucose from the blood (in response to increased insulin production). [1] Absorbed glucose is respired, [1] or it is converted to glycogen (for storage). [1][6 marks]5aA condition in which the blood glucose control mechanism fails. [1]biA symptom of diabetes is a sign that shows/suggests that someone has diabetes. [1] A long-term effect is a condition that can arise if a person has had diabetes for a long period of time and/or their control of blood glucose has not been effective. [1]iiSymptomsLong-term effectsLethargyGlucose in the urineKidney failureEye damageAll correct = 2 marks; one alternative in the wrong column = 1 mark[5 marks]Excretory system and osmoregulation6aiUreter → bladder → urethra [1]iiEvaporation of sweat [1]; evaporation during breathing [1]; urine [1]bIf the blood is too dilute, the kidney reabsorbs less water/if the blood is too concentrated, the kidney reabsorbs more water. [1] Therefore, more urine is produced/less urine produced. [1] The amount of water reabsorbed is controlled by the hormone ADH. [1][7 marks]Plant hormones7aPhototropism is the differential growth of cells caused by the uneven distribution of the hormone auxin in response to unidirectional light. [1]bAny four from:Auxin is produced in stem/shoot tips.It moves down the shoot (to the cells where it acts).More auxin moves to the shaded side of the shoot/less auxin on the more illuminated side.The cells elongate more on the shaded side (due to the presence of more auxin)/cells elongate less on the more illuminated side (due to the presence of less auxin).The shoot/stem bends in the direction of the light. [4][5 marks]Exam-style questions1aiLeft to right [1]iiThe transmitter chemical [1] diffuses [1] from the end of the (first) neurone across to the adjacent (second) neurone. [1] If in high enough concentration, it will trigger an impulse in the second neurone. [1]iiiSo that the time needed for the transmitter chemical to diffuse is as short as possible, [1] allowing overall time for impulse to travel along neurone pathway to be as short as possible. [1]bTransmission at synapses is slower than along neurones. [1] The fewer synapses, the faster the nervous system action will be. [1][9 marks]2aNegative feedback [1]bType 1 treated by insulin/type 2 by diet [1]ciAge of diagnosis decreases with time [1]iiAny two from:less exercise (in population)more obesity (in population)more sugar in diet/carbohydrate-rich dietsbetter diagnosis [2]iiiNumber of patients diagnosed over time [1]diAny three from:many people having diabetesexpensive blood-monitoring instrumentscosts of staffing/educationcosts of treating complications [3]When you are asked to ‘use the information provided’, you will not be able to access all the marks without referring to, or at least using some of, the information provided. An important skill is being able to work out which parts of the information provided are necessary or helpful. iiFewer people with complications [1]; healthier patients/less cost to the NHS [1][11 marks]3aThe control of water balance in the body. [1]bRenal artery [1]ciImmediately after exercise/during the first 3 hours, more ADH is produced. [1] It then falls and levels off. [1] (Plus appropriate use of data from the table.) [1]iiA small volume of urine is produced [1] as more water is reabsorbed (back into the blood). [1] This is due to: loss of water in sweat [1]; exercise/it being a hot day. [1]You should be aware of the circumstances in which the kidneys are likely to reabsorb more water and that if there is more reabsorption, there will be less urine produced.Part i asks you to describe the results and part ii asks you to explain the results. It is important you know the difference between these two command terms and that you answer the question asked.[9 marks]Ecological relationships and energy flowBiological terms and fieldwork1aPopulation — the number of organisms of a single species in an area. [1]Ecosystem — the relationship between all the species in an area and their environment. [1]bCompetition [1]; predation [1][4 marks]2a0.5 m [1]biUse random numbers to identify, for example, 20 quadrat positions. [1] Count the number of plantain plants in the quadrat when in each position. [1] Calculate the average number per quadrat (over the 20 quadrats). [1] Calculate the average number per square metre and multiply by the area of the pitch in square metres (or equivalent calculation). [1]ii20 plants per square metre [1]football pitch = 5000 square metres [1]5000 × 20 = 100 000 plants [1][8 marks]Food chains, food webs and energy flow3ai1 [1]ii3 [1]bAppropriate sketch with:four correctly labelled bars [1]the correct sequence, i.e. producer at bottom, primary consumer next, and so on [1]each bar symmetrical about the central axis [1]cThere is energy lost at each step in a food chain. [1] The fewer the steps, the less energy lost. [1][7 marks]Decomposition, the carbon cycle and global warming4aiDecomposition is the breakdown of dead organic (once-living) material. [1]iiBacteria [1]bEnzymes are released from the fungus. [1] Digestion takes place outside the body/is extracellular. [1] Digested products are absorbed back into the fungus. [1][5 marks]5aPhotosynthesis [1]bR labels on all three respiration arrows (from organic compounds in plants, organic compounds in animals and microbes decaying plants and animals to the carbon dioxide in atmosphere box) [1]cC label on the combustion arrow (from fossil fuels to the carbon dioxide in atmosphere box) [1][3 marks]Minerals and the nitrogen cycle6aMineralFunctionMagnesiumFor (making) chlorophyll [1]Calcium [1]For making cell wallsbiFarmyard manure/slurry/compost [1]iiAny two from:improves soil qualityno costnutrients released slowlyless likely to leach into waterways (so less likely to cause eutrophication) [2][5 marks]7aiOn the outer surface/the outermost cell layer of roots [1]iiThe cell should show a cell wall with thin ‘hair’/extension [1] and the cytoplasm extending into the ‘hair’/extension. [1] All four labels correct = 2 marks; any three labels correct = 1 mark (labels are only awarded if the structures are correctly drawn).bThe transport of minerals/substances against the concentration gradient/from low to high concentration [1]; using energy [1] from respiration. [1][8 marks]Eutrophication and human activity and biodiversity8aiNitrate [1]iiSewage disposal/fertiliser runoff [1]bMicroorganisms/bacteria are aerobic/use oxygen to respire [1] during the decomposition of dead plants/algae. [1] Animals die due to oxygen shortage (for respiration). [1][5 marks]9aThe planting of woodland in areas where forest had once grown but had been removed. [1]biAny two from:It replaces habitats.It prevents the removal of other woodland habitats.It provides food/shelter for animal species. [2]iiIt maintains/increases the amount of woodland. [1] It helps reduce/slow down the build-up of carbon dioxide levels in the atmosphere. [1][5 marks]Exam-style questions1aBelt transect [1]bi(17/40) × 100 [1]= 42.5% [1]iiSeaweed present from 1 m to 21 m/low tide mark to 21 m/1st to 21st quadrat positions [1]; but none between 15 m and 18 m/15th and 18th quadrats. [1] No seaweed above 21 m. [1]iiiAble to withstand strong tides/wave action/only able to withstand drying out for short periods of time/any other appropriate example. [1]cipH meter/pH probe/any other appropriate example [1]iiCorrect example, e.g. wind speed, water, light, temperature [1]; apparatus linked to choice [1][10 marks]2aAny two from:waterlightspaceminerals [2]biAny five from:rhododendron lets very little light throughpreventing other plants from photosynthesisingit spreads rapidly/is largeleaving little space available for other plantsother plant species die out/cannot growthis results in fewer habitats/less food for animals [5]iiCut them down/any other appropriate example. [1]cFood/territory/mates [1][9 marks]3aiThe temperature in the compost bin increased to a peak. [1] It then fell again. [1] (Plus appropriate use of data from the table.) [1]iiOver time, the decomposing microorganisms produced heat [1] due to respiration. [1]iiiTo allow oxygen to enter [1] for aerobic respiration [1] by decomposing microorganisms. [1]'Oxygen’ is necessary for the first marking point — ‘air’ is not specific enough.bDecomposition takes place faster in warmer temperatures. [1]ciAs fertiliser concentration increases, the number of root nodules decreases (or converse). [1]iiFertiliser contains nitrate. [1] At high nitrate levels, root nodules are less beneficial/plants are less likely/fail to develop root nodules. [1] This is because nitrate levels in the soil are already high (or converse). [1]dAny four from:in waterlogged fields, nitrification is less likely to take placebecause nitrifying bacteria are aerobicwaterlogged fields contain less oxygenso there is more denitrification in waterlogged fieldswaterlogged fields contain less oxygen (allow this bullet point once only)denitrifying bacteria are anaerobic [4]For the third bullet point, it is important to specify that there is ‘less oxygen’ (rather than ‘less air’).[17 marks]4Indicative content:increased use of fossil fuelsand deforestationleads to an increase in atmospheric carbon dioxidethis forms a (‘greenhouse’) layer in the atmospherethat traps heat escaping (leading to global warming)leading to increased temperaturesmelting ice caps/rising sea levels/floodingincreasing frequency of extreme weatherloss of habitatsBandResponse MarksAThe candidate selects at least six of the indicative points.The relevant material is organised with a high degree of clarity and coherence.There is widespread and accurate use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently high standard to make the meaning clear.5–6BThe candidate selects at least four of the indicative points.The relevant material is organised with some degree of clarity and coherence.There is some use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently competent standard to make the meaning clear. 3–4CThe candidate selects at least one of the indicative points.The organisation may lack clarity and coherence.There is little use of specialist vocabulary.Presentation, spelling, punctuation and grammar may be such that the meaning is not clear. 1–2DResponse not worthy of credit.0[6 marks]Marks are often lost in QWC questions due to students not answering the question exactly as it was asked. In this case, it should be clear that marks are going to be awarded for ‘process’, ‘causes’ and ‘problems’, so your answer should address each of these (you will see that the indicative points in the mark scheme include marks for each of these).You will also need to be specific and have enough detail where appropriate. For example, in the first indicative point, the ‘increased’ is important — there would not be a mark for ‘burning fossil fuels’.Unit 2: Body systems, genetics, micro-organisms and healthOsmosis and plant transportOsmosis1aOsmosis is the diffusion of water (molecules) from a dilute solution to a more concentrated solution, [1] through a selectively permeable membrane. [1]b3 — 1 — 2 [1][3 marks]2aThe sucrose is more concentrated than the cells in the potato. [1] Water moves by osmosis from the potato into the sucrose (causing the loss in mass). [1]bCell membrane [1][3 marks]Transpiration3aMesophyll [1]; air spaces [1]; stomata [1]bThe higher the temperature, the faster the transpiration (up to a limit). [1] This is because water evaporates faster in higher temperatures [1] from the mesophyll cells. [1][6 marks]4aiBubble (potometer) [1]iiRecord the distance the bubble moves. [1] Record the time taken. [1] Repeat and average. [1] (Method of creating different humidity conditions described, e.g. with and without a plastic bag around the plant.) [1]iiiRate of transpiration would be lower in more humid conditions. [1]bTransport [1]; photosynthesis [1][8 marks]Exam-style questions1ai(1/61) × 100 [1]= ?1.7% [1]ii7.5% [1]bi11.5% to 12.5% [1]iiThe sweet potato cells are more concentrated than the potato cells. [1] Therefore, more water enters the cells by osmosis because the concentration gradient is larger/water will enter the sweet potato cells even when in relatively high sucrose concentrations. [1]iiiAny two from:length of time cylinders were in solutionspotato and sweet potato of similar agethickness of cylinders [2][8 marks]2aiAt low wind speeds, the rate of transpiration increased as wind speed increased. [1] The rate of transpiration levelled off at higher wind speeds. [1] (Plus appropriate use of data from the graph, e.g. levelled off from 9.5 arbitrary units.) [1]ii(At low wind speeds) higher wind speeds increased the rate of evaporation [1]by increasing the concentration gradient/preventing levels of humidity around the leaf surface from increasing. [1] At higher wind speeds, evaporation was occurring at a maximum. [1]iiiAt night (many) stomata are closed. [1] This makes it more difficult for water to escape from the leaf. [1]biThe greater the leaf surface area, the faster the rate of transpiration. [1] This is due to there being more stomata. [1] Most evaporation/transpiration takes place through the stomata. [1]iiAdvantage — it reduces water loss (at a time when less water is available). [1]Disadvantage — it reduces photosynthesis. [1][13 marks]The circulatory systemBlood and blood vessels1aRed blood cell — transports oxygen [1]White blood cell — defence against disease [1]bRed blood cell [1][3 marks]2aFeatureBlood vesselArteryVeinCapillaryWalls are thick (relative to lumen)YesNo [1]NoPresence of valvesNoYesNo [1]Carries blood under high pressureYesNo [1]NobiPulmonary artery [1]iiArtery [1][5 marks]3aAorta; renal artery; kidney [2]1 mark for two structures in the correct sequencebAny three from:under less pressurecontains less oxygencontains more carbon dioxidecontains less ureacontains less watercontains less glucose [3]‘Under less pressure’ is an appropriate answer because the question asks for ways in which the blood will be different. If it had asked for ‘differences in composition’, then this would not be credited.[5 marks]The heart4aiRight ventricle [1]iiPulmonary vein (entering the left atrium) correctly labelled [1]iiiPrevent the blood flowing backwards/ keep the blood flow unidirectional [1] from the left ventricle into the left atrium when the ventricle contracts [1]bVentricles pump blood around the body/to the lungs. [1] Atria pump blood into ventricles only/a shorter distance. [1][6 marks]5aiThe volume of blood pumped by the heart per minute [1]iiIncreases cardiac output [1]bStrengthens the heart muscle [1][3 marks]Exam-style questions1aAny two from:biconcave shape [1] — greater surface area across which oxygen can diffuse [1]absence of a nucleus [1] — more space for haemoglobin [1]presence of haemoglobin (containing iron) [1] — to transport oxygen [1]bMore blood delivered per unit time [1]; carrying oxygen and glucose [1]; for respiration (to release energy for muscle contraction). [1] This allows aerobic respiration to continue for longer/allows muscle contraction to continue for longer. [1]The first 3 marks describe the effect of the increased pulse rate, whereas the fourth mark is for explaining the ‘advantage’ of the increased pulse rate.cThe red blood cells would take in water. [1] This would cause them to expand and burst/cell lysis would take place. [1][10 marks]2Indicative content:arteries have thick walls as blood at high pressuremuscle provides strengthelastic fibres allow expansion and recoil (as blood pulses through)veins have thin walls as blood under less pressurewith less muscle/elastic fibreslarge lumen reduces friction between blood and walls (to aid flow as under less pressure)valves prevent backflow of bloodcapillary walls one cell thickaids exchange (between blood and tissues)as walls are permeableBandResponse MarksAThe candidate selects at least six of the indicative points.The relevant material is organised with a high degree of clarity and coherence.There is widespread and accurate use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently high standard to make the meaning clear.5–6BThe candidate selects at least four of the indicative points.The relevant material is organised with some degree of clarity and coherence.There is some use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently competent standard to make the meaning clear. 3–4CThe candidate selects at least one of the indicative points.The organisation may lack clarity and coherence.There is little use of specialist vocabulary.Presentation, spelling, punctuation and grammar may be such that the meaning is not clear. 1–2DResponse not worthy of credit.0[6 marks]Reproduction, fertility and contraceptionThe male and female reproductive systems1aStructureFunctionTestisProduces sperm [1]Prostate gland [1]Nourishes spermSperm tubesCarry sperm from testes to urethra/penis [1]biTo swim to the egg/through the female reproductive system, [1] over very long distances (relative to the size of the sperm). [1]iiPresence of a flagellum (for swimming) [1]iiiOviduct [1][7 marks]Infertility2aAny two from:failure of ovaries to produce eggsoviducts being blockedcomplications of some STIslining of uterus does not develop properlyvagina may be hostile to (and kill) sperm [2]If this question appeared in an exam, a significant minority of students would drop 1 or 2 marks by giving a cause (or causes) of infertility in males, showing the importance of always reading the question carefully.bFertilisation outside the body/in a laboratory/in a test tube [1]cMitosis [1]diTo increase the chance of the treatment being successful/the chance of success with IVF treatment is not high. [1]iiThe embryos implant [1] in the lining of the uterus. [1][7 marks]Contraception3aThey release hormones [1] that prevent the growth of an egg/ovulation. [1]biThe oviducts are cut, [1] preventing the egg from travelling down the oviduct/ preventing the sperm from reaching the egg. [1]iiAdvantage — very reliable [1]Disadvantage — very difficult to reverse/does not protect against STIs [1][6 marks]Exam-style questions1aiX — umbilical cord [1]Y — amnion [1]iiAmniotic fluid correctly labelled (within amnion) [1]iiiHolds the amniotic fluid in place. [1] Protects/cushions the foetus. [1]ivDissolved nutrients/or by example (e.g. glucose/amino acids) [1]; oxygen [1]bThey extend the surface area (of the boundary between placenta and uterine wall). [1] This helps/speeds up the transport of substances between the mother and the foetus. [1]cThe amnion ruptures/breaks, [1] releasing the amniotic fluid. [1]Although birth is not specifically on the specification, students would be expected to be able to deduce changes that would take place in the uterus before birth.[11 marks]2aThe thickness of the uterine lining falls until day 5. [1] It then increases again (back to a maximum). [1]Thickness falls then rises = 1 mark; reference to day 5 is needed to obtain both marks.bDays 13–14. [1] This is because oestrogen stimulates ovulation and ovulation takes place around day 14/oestrogen is responsible for the build-up/repair of the uterine lining (and the lining is back to full thickness by day 14). [1]ciProgesterone [1]iiFertilisation will only take place around this time. [1] The thick lining allows implantation to take place. [1]dMenstruation takes place (again). [1][8 marks]Genome, chromosomes, DNA and geneticsThe genome, chromosomes, genes and DNA1Genome [1]; chromosomes [1]; genes [1][3 marks]2aiSugar [1]; phosphate [1]; bases [1]iiDouble helix [1]bThree bases [1] along the coding strand/one strand of DNA [1] code for one amino acid. [1][7 marks]Cell division3aGrowth [1]; replacing worn-out cells [1]; repairing damaged tissue [1]bType of cell divisionMitosisMeiosisWhere it takes placeThroughout the bodyIn reproductive organs/testes and ovaries [1]Comparison with parental cellSame number of chromosomes and the chromosomes are the same [1]Daughter cells have half the number of chromosomesComparison with other daughter cellsSame number of chromosomes and the chromosomes are the sameSame number but different chromosome combinations from other daughter cells [1][6 marks]Genetic diagrams, terminology and genetic conditions4aiIn the heterozygous condition, the dominant allele overrides the recessive allele/determines the phenotype. [1] The recessive allele only shows itself in the phenotype if there are two recessive alleles. [1]iiHomozygous means that both alleles of a gene are the same. [1] If heterozygous, the two alleles are different (one dominant and one recessive) [1]Many students find it much easier to identify dominant and recessive alleles or homozygous and heterozygous genotypes in genetic diagrams than try to explain what they mean. Nonetheless, you should be able to explain each of the genetic terms, so it is worthwhile spending time learning a definition of each.biheterozygous x heterozygous [1]iiheterozygous × homozygous recessive [1][6 marks]5A test cross is used to identify the unknown genotype of a dominant phenotype. [1] The unknown genotype is crossed with an individual that is homozygous recessive. [1] If any of the offspring have the recessive phenotype the unknown individual is heterozygous (for the gene concerned)/if no offspring have a recessive phenotype the unknown individual is homozygous (for the gene concerned). [1][3 marks]6aDown’s syndrome [1]bHuntington’s disease [1]cDown’s syndrome [1]dHaemophilia [1][4 marks]Genetic screening and genetic engineering7aiChecking for the presence of (harmful) genetic conditions in an individual. [1]iiInsurance may be difficult to get/could be more expensive/bias in the workplace/ any other appropriate example. [1]bAdvantage — it is more accurate. [1]Disadvantage — there is a risk of miscarriage with amniocentesis. [1][4 marks]Exam-style questions1aIndicative content:backbone of sugar and phosphatelinked by basesbases join A–T and C–Gto form a double helixone strand/coding strand codes for amino acidbase triplet hypothesis/explanation of three bases coding for an amino aciddifferent bases code for different amino acidsamino acids join together to form proteinBandResponse MarksAThe candidate selects at least six of the indicative points.The relevant material is organised with a high degree of clarity and coherence.There is widespread and accurate use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently high standard to make the meaning clear.5–6BThe candidate selects at least four of the indicative points.The relevant material is organised with some degree of clarity and coherence.There is some use of specialist vocabulary.Presentation, spelling, punctuation and grammar are of a sufficiently competent standard to make the meaning clear. 3–4CThe candidate selects at least one of the indicative points.The organisation may lack clarity and coherence.There is little use of specialist vocabulary.Presentation, spelling, punctuation and grammar may be such that the meaning is not clear. 1–2DResponse not worthy of credit.0bAny three from:during fertilisation male and female gametes combinemeiosis halves the number of chromosomesso that during fertilisationthe normal chromosome number is achieved (if no meiosis, the chromosome number would double each time) [3][9 marks]2aMales are XY and females are XX. [1] Half of all male gametes are X and half Y. [1]Therefore, 50% of XX and 50% of XY are expected (after fertilisation). [1]biNormal (carrier) [1] female [1]iiXBXbXBXBXBXBXbYXBYXbY1 mark for the correct gametesGenotypes:XBXB XBXbXBYXbY [1]Phenotypes:Normal femalesNormal maleColour-blind male [1]Ratio:2:1:1 [1]This question specifically asks for the genotypes and phenotypes produced and the ratio of these in the offspring, so marks are awarded for each of these (as well as for the correct gametes). The ratio is shown as 2:1:1, as you are specifically asked to give the ratio of phenotypes. If you had been asked to show the ratio of genotypes, it would have been 1:1:1:1.[9 marks]3aThe modification of the DNA in an organism to introduce desirable characteristics. [1]biInsulin reduces blood glucose/sugar level. [1]iiAny two from:animal insulin is different from human insulinavoids possibility of transferring virusescan produce the quantities neededfewer ethical issues [2]ciRestriction enzymes [1]iiSticky ends [1]iiiIt allows the insulin gene to join with the plasmid, [1] using matching base pairs. [1]dExtraction — the removal of the insulin (from the medium in which it was made, e.g. bacteria). [1]Purification — the removal of all debris to produce a pure form of the insulin. [1][10 marks]Variation and natural selectionTypes of variation1aType of variationExampleHow normally represented in graphsContinuousHeight/length/any other appropriate example [1]HistogramDiscontinuous [1]Tongue rollingBar chart [1]The specification states that continuous variation is normally represented by histograms. However, in exam questions you may see it represented by a line graph, particularly if just giving general trends (discontinuous variation should never appear as a line graph).bMutations [1]; chromosomes [1]; gene [1]; environment [1][7 marks]Natural selection2ai2 — 3 — 1 [1]iiAntibiotic resistance/any other appropriate example [1]biGradual change in the organisms (of a species) over time. [1] The formation of new species. [1]iiThey can show/provide evidence that organisms have changed over time. [1] They can show how they changed (the different stages as they evolved). [1]cExtinction [1][7 marks]Selective breeding3Any two from:appearanceincreased food qualityquantitydisease resistanceany other appropriate example [2][2 marks]Exam-style questions1ai62 – 3 [1]= 59 [1]It is important to read all the questions carefully, and a seemingly straightforward one like this is no exception. Did anyone calculate the difference in numbers between blood groups A and O (the most obvious bars)?iiDiscontinuous [1]iiiTongue rolling/hand dominance [1]ivGenetic [1]bHeight in humans is continuous variation. [1] The causes are (mainly) genetic [1]and (partially) environmental. [1][8 marks]2aiSome plants had more toxins than other plants/phenotypes varied in terms of toxin concentrations. [1] The plants with more toxin were more able to avoid being eaten by slugs. [1] The plants with no (or small levels of) toxin had no defence against being eaten by slugs. [1] The plants with toxin were more likely to survive and pass their genes on to the next generation. [1] Over time, the number of plants with high levels of toxin increased/the number of plants with low levels of toxin decreased. [1]iiThe number of garlic plants would decrease. [1] This is because they would have no defence against the slugs/very low toxin levels would not protect against the slugs. [1]biY — much less variable [1]ii(Selective breeding) by humans. [1] Only those plants with high yields were used to breed. [1] Over many generations all the plants had a high yield. [1]iiiSelective breeding involves humans/humans are not involved in natural selection/ (normally) selective breeding is a faster process than natural selection. [1][12 marks]Health, disease, defence mechanisms and treatmentsCommunicable diseases and the body’s defence mechanism1aA disease that can be passed from one organism/person to another. [1]bName of diseaseHow spreadPreventionTreatmentChlamydiaSexual contact [1]Using a condomAntibiotics [1]SalmonellaContaminated foodAlways cooking food thoroughly/not mixing cooked and uncooked food [1]AntibioticsTuberculosisAirborne/droplet infection [1]VaccinationAntibiotics (and other drugs)[5 marks]2aThey trap/catch the microorganisms responsible [1] and prevent them entering further into the body. [1]For the first mark, it is important to describe how the mucous membranes work, for example, they 'trap' or 'catch' the microorganisms. Answering that the membranes prevent the microorganisms getting into the body is awarded the second mark only.biThe presence of an (unknown/harmful) antigen in the body. [1]iiLymphocyte [1]iiiThe antibodies are a complementary shape to the antigens on the microorganisms. [1] They fit together/latch on to the microorganisms. [1] This clumps them together/stops their spread. [1][7 marks]Development of medicines, antibiotics and vaccinations3Fleming [1]; Florey [1]; Chain [1]Florey and Chain can be in either order.[3 marks]4StageDescription of stageReason for stagePreclinical trials — in vitro (in lab)Testing on living cells/tissues in the laboratory [1]Checks that the drug is effective and not poisonous before testing on living organismsPreclinical trials — animal testingTesting on animals (living organisms)Avoids testing on humans at this stage/checks for side effects [1]Clinical trials [1]Testing on human volunteers (and patients)Finding the optimum dosage[3 marks]5aiBacteria that are resistant to a range of antibiotics. [1]iiMRSA/any other appropriate example [1]bAny two from:increased levels of hygieneisolation of infected patientsreduced use of antibiotics [2][4 marks]6aTo prevent the person receiving the vaccination from getting the disease. [1]biThere are more antibodies produced. [1]iiMemory lymphocytes (for that microorganism) [1] were already present in the body. [1]cThe antibodies are produced by the body. [1][5 marks]Non-communicable diseases7aiSkin cancer [1]iiUV radiation (in the sunlight) [1] causes mutations in skin cells. [1]bNicotine [1][4 marks]8a2 — 3 — 4 — 1 [2]Correct sequence = 2 marks; any two in correct sequence = 1 markbAngioplasty uses balloon-like structures to hold open diseased arteries. [1] This allows stents to be inserted. [1][4 marks]9aMalignant tumours are not surrounded by a capsule. [1] Malignant tumours can spread throughout the body. [1]biAdvantage — no side effects/appropriate comparison with other named treatment. [1]Disadvantage — not suitable if the cancer has spread/some parts of the body are inaccessible for surgery. [1]iiChemotherapy/radiotherapy/immunotherapy [1][5 marks]Aseptic techniques10aAutoclaving [1]bTo prevent the lid coming loose and therefore contamination of the culture or the surrounding area/people. [1]cInoculation [1][3 marks]Exam-style questions1aiVirus [1]iiBy droplet infection/any other appropriate explanation [1]bThe antigens are slightly different (in each strain of flu). [1] This means that someone could have antibodies that are complementary to/match/could combine with some strains and not others. [1] That person will only be immune to those strains in which antibody–antigen reactions/combinations can take place. [1]The term ‘antigen’ is important for the first marking point — normally, it is not enough in this type of question to state that the microorganisms are different. In terms of an antibody–antigen reaction, the microorganisms are different because their antigens are different.ciFlu is caused by a virus. [1] Antibiotics only work on bacteria. [1]iiMutations/changes [1] to the DNA in bacteria [1] give them new properties [1] that allow them to be able to defend against antibiotics. [1][11 marks]2aiA disease that is not passed from person to person/that is not infectious. [1]iiGenetics [1]; lifestyle [1]biBronchitis [1]; emphysema [1]iiAny five from:Bronchitis (by narrowing the bronchi and bronchioles) reduces the amount of air reaching the lungs.Emphysema reduces the gas exchange area.This reduces the amount of oxygen entering the blood. (Allow once to link with either of the first two bullet points.)Carbon monoxide combines with red blood cells.This prevents the cells affected from carrying oxygen.Less oxygen reaches the muscles for respiration (to provide energy). [5]ci(10/400) × 100 [1]= 2.5% [1]iiOverall, the drug had no effect/had minimal effect. [1] However, it prolonged life in the early stages/years. [1] (Plus appropriate use of data from the table to support either of first two marking points.) [1]iiiAs a control (or by explanation) [1][16 marks]3aThe inoculating loop should not have been placed immediately into the culture bottle (it should have been allowed to cool first to prevent the bacteria being killed). [1] The Petri dish lid should not have been placed on the bench (it should have only been partially opened to restrict the possibility of contamination). [1] The loop and culture bottle should not have been placed in the sink for washing (it should have been autoclaved or disposed of, according to the teacher’s instructions). [1]biAdd alcohol (water) and grind the leaves from each species in separate mortars to make an aqueous solution. [1]Soak one (or more) of the absorbent discs of filter paper in the garlic solution and repeat the same process for the mint. [1]Transfer the discs to (separate) Petri dishes that has been inoculated/plated with a bacterium or fungus. [1]Incubate at 25°C for 24–48 hours and compare zones of inhibition (if any). [1]iiAny two from:The same mass of leaves from each species and same volume of water should be used to form the aqueous solutions.The discs should be left in the aqueous solutions for the same length of time.The same species of bacteria or fungus should be used to inoculate each Petri dish.The plates should be incubated for the same length of time.The plates should be incubated at the same temperature. [2]iiiThick cell walls/waxy cuticles/production of poisonous chemicals [1][10 marks]4aThere is an increased chance of survival with early detection. [1] This is because the cancer can be treated before it spreads (and becomes inaccessible). [1]bSo the path of radiation into the body changes. [1] This avoids/reduces damage to healthy cells. [1]cThe patient is given antibodies that attach to antigens [1] on the cancer cells. [1] This targets the cancer cells so that the immune system/body’s defence system can locate and destroy them. [1][7 marks] ................
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