Cambridge A Level Biology 9700 — 2015 Oct/Nov Paper 2 · Variant 3

This document consists of 16 printed pages. DC (NF/JG) 99037/3 © UCLES 2015 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 8 8 5 5 7 6 6 9 4 1 * BIOLOGY 9700/23 Paper 2 Structured Questions AS October/November 2015 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name in the spaces provided at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. You may lose marks if you do not show your working or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question.

2 9700/23/O/N/15 © UCLES 2015 Answer all the questions 1 Antibodies are secreted by activated B-lymphocytes known as plasma cells. Fig. 1.1 is a diagram showing the cellular processes involved in the production of a polypeptide of an antibody molecule (not drawn to scale). DNA mRNA A D B 1 2 3 C Fig. 1.1

3 9700/23/O/N/15 © UCLES 2015 [Turn over (a) (i) Name structures A, B and C. A … B … C … [3] (ii) Name molecule D. D … [1] (iii) State what is occurring at 1, 2 and 3. at 1 … … at 2 … … at 3 … … [3] (b) Antibodies are glycoproteins. State what is meant by the term glycoprotein. … … … [1] (c) The genes responsible for antibody production are found on different chromosomes, such as chromosomes 2 and 14 in humans. Explain how one antibody molecule is the product of more than one gene. … … … … … [2]

4 9700/23/O/N/15 © UCLES 2015 (d) Describe and explain how the structure of an antibody molecule is related to its functions. … … … … … … … … … [4] [Total: 14]

5 9700/23/O/N/15 © UCLES 2015 [Turn over Question 2 starts on page 6

6 9700/23/O/N/15 © UCLES 2015 2 Most of the water lost from plants passes out through the stomata of leaves. The distance between open guard cells is known as the stomatal aperture, as shown in Fig. 2.1. stomatal aperture Fig. 2.1 Researchers investigated the effect of stomatal aperture on rates of transpiration in leaves of Tradescantia zebrina under two conditions: • air kept moving by a fan (moving air) • non-moving air. The results are shown in Fig. 2.2. 0 0 5 10 15 20 10 20 30 40 50 60 70 80 90 100 stomatal aperture / +m rate of transpiration / g m–2 h–1 moving air non-moving air Fig. 2.2

7 9700/23/O/N/15 © UCLES 2015 [Turn over (a) (i) Compare the effect of stomatal aperture on the rate of transpiration in T. zebrina in the two conditions. … … … … … … … [3] (ii) Explain the effect of stomatal aperture on rates of transpiration in non-moving and moving air. … … … … … … … [3]

8 9700/23/O/N/15 © UCLES 2015 (b) Spruce trees and pine trees are adapted to dry conditions where water can be in limited supply. Fig. 2.3 shows two stomata in a spruce leaf and Fig. 2.4 shows a vertical section through a stoma from a pine leaf. Fig. 2.3 Fig. 2.4 (i) Explain how the stomatal features shown in Fig. 2.3 and Fig. 2.4 give an advantage to plants such as spruce and pine. … … … … … [2] (ii) Some plants that live in very dry conditions close their stomata during the day and open them at night. State one disadvantage of this for these plants. … … [1] (iii) State and explain two adaptations that plant leaves have for survival in dry conditions other than those involving number or structure of stomata. 1. … … 2. … … [2] [Total: 11]

9 9700/23/O/N/15 © UCLES 2015 [Turn over Question 3 starts on page 10

10 9700/23/O/N/15 © UCLES 2015 3 The enzyme catalase is found in many plant and animal tissues. The enzyme catalyses the decomposition of hydrogen peroxide, which is a toxic product of metabolism. The reaction is: catalase 2H2O2 O2 + 2H2O A research team investigated the activity of two forms of catalase, P and Q, extracted from Anopheles gambiae, an important vector of malaria. The team investigated the effect of increasing concentrations of hydrogen peroxide on the activity of these two forms of catalase. The results are shown in Fig. 3.1. 120 140 80 100 40 60 20 0 0 50 100 150 200 250 300 concentration of hydrogen peroxide / mM activity of catalase / arbitrary units catalase P catalase Q Fig. 3.1 (a) With reference to Fig. 3.1, describe and explain the effect of increasing the concentration of hydrogen peroxide on the activity of catalase P. … … … … … … … … … … … [5]

11 9700/23/O/N/15 © UCLES 2015 [Turn over (b) Each molecule of catalase consists of four identical polypeptides. The two forms of catalase in A. gambiae differ by only one amino acid at position 2 in the amino acid sequence. Catalase P has serine and catalase Q has tryptophan. Suggest how the difference in one amino acid is responsible for the lower activity of catalase Q compared with catalase P. … … … … … [2] (c) Female mosquitoes feed on blood in order to produce their eggs. After feeding, the metabolic rate increases for egg production. The researchers allowed female mosquitoes to feed on blood. They found that female mosquitoes with only catalase P produced more eggs than those with only catalase Q. Suggest why there is a difference in egg production between the two types of A. gambiae. … … … … … [2] (d) Metal ions can act as a non-competitive inhibitor of catalase. Explain how copper ions can act as a non-competitive inhibitor. … … … … … [2]

12 9700/23/O/N/15 © UCLES 2015 (e) Enzyme inhibitors can also inhibit carrier proteins in cell surface membranes. Explain why carrier proteins are required in cell surface membranes. … … … … … [2] (f) Describe three roles of cell surface membranes, other than the transport of substances into and out of cells. 1. … … 2. … … 3. … … [3] [Total: 16]

13 9700/23/O/N/15 © UCLES 2015 [Turn over 4 Glycogen is a highly branched polysaccharide molecule that is stored in the liver, kidney and muscles of mammals. Fig. 4.1 shows a small part of a molecule of glycogen. CH2OH C O O H H C H OH H C C C O CH2OH CH2 C O H H C H OH H C C C O CH2OH C O O H H C H OH H C C C O C O H H C H OH H C CH2OH C O H OH H H C H OH H OH H OH H OH H OH H C C C O C C O X Fig. 4.1 (a) (i) Name the bond at X. … [1] (ii) State the advantages for a mammal of having a storage molecule that is highly branched. … … … … … … … [2] (iii) State two ways in which the structure of cellulose differs from the structure of glycogen. 1. … … 2. … … [2]

14 9700/23/O/N/15 © UCLES 2015 (b) Glycogen from animals and starch from plants form a large part of the energy intake of humans. Fig. 4.2 is a flow chart that shows the energy input, in one growing season, into a field of a cereal crop which is processed to provide animal feed. solar energy = 9 × 107 kJ energy absorbed by cereal plants in photosynthesis processing to produce 140 kg of animal feed energy in the cereal crop harvested = 4 500 000 kJ energy in feed = 2 000 000 kJ initial mass of animals = 25 kg final mass of animals = 75 kg mass gain in 12 weeks = 50 kg energy in 50 kg of animals for human consumption = 385 000 kJ Fig. 4.2 (i) Calculate the percentage of the energy in animal feed that is converted into energy available for human consumption. Show your working. answer … [2]

15 9700/23/O/N/15 © UCLES 2015 [Turn over (ii) Explain why the energy available to humans from feeding on animal products is much less than if the energy came directly from crop plants, such as cereals. … … … … … … … … … [3] [Total: 10] 5 Nicotine and carbon monoxide in tobacco smoke contribute to damage to the cardiovascular system. (a) Explain how nicotine and carbon monoxide contribute to damage to the coronary arteries. nicotine … … … … carbon monoxide … … … … [3]

16 9700/23/O/N/15 © UCLES 2015 (b) One type of surgical treatment for coronary heart disease is to use arteries from the chest and veins from the leg to by-pass blockages as shown in Fig. 5.1. vein (from leg) plaque blockage internal mammary artery (from chest) aorta Fig. 5.1 (i) Explain how the two by-passes shown in Fig. 5.1 provide an effective treatment for coronary heart disease. … … … … … … … [3] (ii) The cost of treating heart disease is very high. Suggest the steps that governments could take to reduce heart disease in the population. … … … … … … … [3] [Total: 9] Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series 9700 BIOLOGY 9700/23 Paper 2 (AS Structured Questions), maximum raw mark 60 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2015 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 Mark scheme abbreviations: ; separates marking points / alternative answers for the same point R reject A accept (for answers correctly cued by the question, or by extra guidance) AW alternative wording (where responses vary more than usual) underline actual word given must be used by candidate (grammatical variants accepted) max indicates the maximum number of marks that can be given ora or reverse argument mp marking point (with relevant number) ecf error carried forward I ignore AVP alternative valid point (examples given)

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 1 (a) (i) A – nuclear envelope ; B – rough endoplasmic reticulum ; R RER / ER / smooth ER C – (large sub-unit of) ribosome ; A ribosomal RNA, R rRNA [3] (ii) D – transfer / t, RNA ; [1] (iii) at 1 – transcription ; A post-transcription modification / removal of introns A DNA / gene, copied (to synthesise mRNA) A genetic information copied R DNA copied onto mRNA R DNA code copied onto mRNA at 2 – amino acid activation ; A attachment / AW, of (specific) amino acid (to specific tRNA) at 3 – translation / condensation of amino acids / formation of peptide bond(s) (between amino acids) ; A codon-anticodon binding I (poly)peptide synthesis [3] (b) a protein combined with, a carbohydrate / sugars / AW ; A protein with sugar R protein with, glycogen / polysaccharide [1] (c) antibody molecule has (2) heavy and (2) light chains / two types of polypeptide / different types of polypeptide ; idea that each different, polypeptide / chain, is coded for by a gene ; ref. to gene coding for enzyme for carbohydrate attachment (to make the glycoprotein) ; [max 2] (d) points can be taken from an annotated diagram 1 variable region / Fab region, has antigen binding sites ; 2 ref. to specificity for binding antigen / complementary (shape) to the antigen ; A idea of sequence of amino acids (on light and heavy chain) giving specific shapes 3 (IgG has) two (antigen) binding sites (per antibody molecule) ; 4 heavy chains / Fc / constant, region binds to (receptors on), phagocytes / named phagocyte ; 5 hinge region gives flexibility when binding to, antigen / pathogen / AW ; 6 disulfide bridges, give stability / hold chains together / AW ; award on a diagram if bond and chains are labelled 7 AVP ; e.g. R groups bind to antigen bind to antigen by, hydrogen bonding / ionic bonding constant region gives antibody class / AW [max 4] [Total: 14]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 2 (a) (i) A Ψ for water potential I moisture A aperture for stomatal aperture throughout both units must be used at least once to award mp3 and mp7 similarities 1 when, stomatal aperture is 0 (µm) / stomata are closed, no, transpiration / water loss ; 2 as stomatal aperture increases rate of transpiration increases in both groups of plants ; 3 comparative use of figures with units in support of mp2 for either condition ; differences in moving air 4 stomatal aperture, influences / controls / AW, rate of transpiration at all apertures ; in non-moving air 5 at stomatal apertures 15 µm and above rate of transpiration does not increase further / reaches a plateau / remains constant ; 6 stomatal aperture has most effect on rate of transpiration in non-moving air at low apertures ; ora comparing moving and non-moving 7 comparative use of figures with units to show rates of transpiration at the same stomatal aperture ; [max 3] (ii) A water vapour potential for water potential 1 ref. to increasing width of stomatal aperture allows more water vapour to diffuse out ; ora R osmosis, R evaporate out I evaporation from mesophyll 2 (intercellular) air spaces in leaf, are fully saturated / have high water potential / AW ; 3 in moving air, water vapour is blown away / does not remain around the leaf ; A low humidity around the leaf, A ora for non-moving air 4 in moving air, water potential gradient, is steep / maintained / increases / AW ; ora for non-moving air, R concentration gradient 5 so in moving air, high / higher, rate of diffusion of water vapour in terms of an idea of a gradient ; A ora [max 3] (b) (i) advantage of having, stomata in pits / AW water vapour / moist air, builds up / trapped, in the, pit / groove / crypt ; A sunken stoma(ta) reduces water potential gradient, between air inside the leaf and outside / AW ; A diffusion gradient less transpiration / less diffusion of water vapour out (through stomata) / water is conserved ; R prevents water (vapour) loss less water needs to be absorbed ; [max 2]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 (ii) treat ‘less gas exchange’ unqualified as neutral cannot absorb carbon dioxide (during the day when photosynthesis occurs) ; rate of photosynthesis is reduced / no photosynthesis ; AVP ; e.g. less water / minerals, reaches leaf cells (for other processes) cooling effect of transpiration does not occur slow growth [max 1] (iii) I moisture 1 leaves, rolled / curled, so, stomata on inside / humid layer builds up / moist air builds up, (in enclosed area) ; A less steep water potential gradient R coiled / curved 2 trichomes / hairs, create, a layer of non-moving air around the leaf / allow humid area to build up ; A less steep water potential gradient 3 (leaves are), thick / succulent, to store water ; 4 thick(er) (waxy) cuticle reduces, transpiration / water loss ; A makes more waterproof, A waxy layer for cuticle 5 reflective cuticles, reduce heat load / AW ; A shiny cuticles reflect heat ; 6 needle-like leaves to reduce surface area (to volume ratio so less, transpiration / water loss) ; A small leaves R spikes / spines, unqualified 7 layers of epidermal cells, to reduce (cuticular) transpiration / water loss ; 8 thick walled epidermal cells, to reduce (cuticular) transpiration / water loss ; 9 ref. to hinge cells, leaf curling / wilting / AW ; A leaves wilt to reduce exposure to the sun ; [max 2] [Total: 11]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 3 (a) description 1 activity / rate, increases to a, maximum / plateau ; A ‘levels off’ / remains constant / reaches Vmax 2 increase in, activity / rate, slows ; 3 data quote with units to support any correct statement ; e.g. mp 1128–132 au at 250–300 mM e.g. mp 2 0 to 120 au between 0 and 100 mM, 120–128 au between 100 and 200 mM A au for arbitrary units explanation at low / increasing, concentration of hydrogen peroxide 4 substrate / hydrogen peroxide, (concentration) is limiting (factor) ; 5 active sites, unoccupied (low concentration) / become more occupied (increasing concentration) ; R active side (penalise once) 6 (low concentration) few collisions between enzyme and substrate / few ESC formed or (increasing concentration) more collisions between enzyme and substrate / increasing ESC formed ; at high (activity slows) / higher (plateau) concentration of hydrogen peroxide 7 enzyme / catalase, concentration / AW, becomes / is, limiting (factor) ; 8 maximum number of enzyme-substrate complexes formed ; A ES complexes / ESCs 9 (all) active sites, saturated / (always) occupied ; A ora [max 5] (b) amino acid at position 2, is part of active site / helps to give shape to active site / helps form the structure of the active site ; plus one from: idea of different, R group / side chain, gives different properties ; A tryptophan has a, hydrophobic / larger, R group / serine has a polar R group, different properties ; (slightly) different, folding of polypeptide / secondary structure / tertiary structure / active site / catalytic site / binding site ; suggested reasons e.g. electrons less easily transferred ref. to induced fit , more efficient with P ; ora different interactions between polypeptides (in catalase) ; [2] (c) 1 increased, metabolic rate / protein metabolism (after feeding) means, increased / more, hydrogen peroxide (produced) ; 2 idea that less effective, catalase / Q, means, more hydrogen peroxide remains / less hydrogen peroxide broken down ; ora more hydrogen peroxide from increased metabolism is broken down faster in P = 2 marks 3 hydrogen peroxide, interferes with / is damaging to / AW, egg production ; 4 AVP ; I ref. to oxygen production and use in aerobic respiration [max 2]

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 (d) bind to, allosteric site / site other than active site ; causes change in (shape of) active site ; A changes shape in active site (so) substrate cannot bind (to enzyme / active site) / enzyme-substrate complex cannot form ; [max 2] (e) needed for, facilitated diffusion / active transport ; A description of active transport e.g. moving, molecules / ions, against a concentration gradient ref. to (some) substances are, water soluble / polar / hydrophilic / ionic / charged ; I large cannot pass through, phospholipid bilayer / hydrophobic core ; [max 2] (f) 1 barrier between cell cytoplasm and, external environment / AW ; e.g. tissue fluid R barrier unqualified R ‘keeps cell contents in’ R ‘membrane surrounds the organelles’ R barrier for water soluble substances 2 receptor for, hormone / neurotransmitter / cell signalling substance / AW ; A signal receptor 3 cell recognition / acts as cell surface antigen ; 4 cell-to-cell adhesion ; 5 site for, enzymes / catalysing reactions ; 6 anchoring the cytoskeleton / AW ; 7 selection of substances that enter or leave a cell ; R controls / regulates substances that enter cell 8 formation of hydrogen bonds with water for stability ; 9 AVP ; e.g. ref. to, changing shape of cell / flexibility of cells e.g. phagocytosis [max 3] [Total:16] 4 (a) (i) (α 1–6) glycosidic ; A glucosidic [1] (ii) many, terminals / ends, for, attachment of glucose / removal of glucose ; glucose can be stored quickly ; glucose can be, mobilised / AW, when required / quickly ; A more easily mobilised / AW A glycogen can be hydrolysed easily makes it more compact / takes up less space / high density ; [max 2] (iii) no branching / single unbranched chain / straight / linear ; different monomer / beta glucose / β glucose ; ora alternate position of monomers in cellulose / AW ; e.g. rotated 180° only one type of (glycosidic) bond / 1–4 only / no 1–6 ; forms hydrogen bonds with other cellulose molecules (to give parallel chains); forms, microfibrils / fibres ; [max 2] (b) (i) max 1 for correct working if no answer or answer incorrect 100 000 000 2 000 385 × 19.25 / 19.3 / 19 ;; [2]

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 (ii) 1 energy lost in processing crops to make animal feed ; animals 2 food, not eaten / wasted ; 3 food, not digested / indigestible / not absorbed / egested or energy lost in, excretion / urea ; 4 energy lost, in respiration / as heat ; A movement / used for metabolism 5 (some) maintain constant body temperature which requires energy ; AW humans 6 energy lost in processing animals for human food ; 7 (named) animals parts not edible ; 8 AVP ; e.g. some animals do not have enzyme to digest cellulose [max 3] [Total:10] 5 (a) I ref. to walls, unqualified I ref. to vasoconstriction nicotine 1 damages the, endothelium / (inner) lining / tunica intima ; 2 increases blood pressure (which can damage the endothelium) ; 3 increases risk of, blood clotting / thrombus formation ; A thrombosis, A increases stickiness of platelets carbon monoxide 4 damages the, endothelium / inner lining / tunica intima ; allow even if mp1 given 5 so increases risk of, blood clotting / thrombus formation ; A thrombosis 6 idea of overall reduced oxygen supply to coronary artery walls ; 7 AVP ; e.g. inflammation / (increases risk of) atheroma or plaque or atherosclerosis [max 3] (b) (i) (the by-pass vessels) supply (oxygenated) blood from the aorta ; supply oxygen to, cardiac / heart / ventricle, muscle ; supply, glucose / fat / fatty acids ; reduce / prevent, anaerobic respiration ; A so (muscles) can (continue to) respire aerobically prevent death of, muscle / heart cells / heart tissue A prevents angina [max 3]

Page 9 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9700 23 © Cambridge International Examinations 2015 (ii) I lifestyles, healthy or otherwise I ‘better health care’ education early education / educate children (about heart disease) or leaflets / posters / continuing education, about effects of heart disease ; diet encourage / educate about, healthy eating / balanced diet ; ref. to labelling of foodstuffs ; tax on, sugar / fats ora e.g. reduce cost of ‘healthy’ foods or idea of regulation against foods with, high sugar / fat ; A junk food smoking educate about dangers of smoking / anti-smoking campaigns ; provide ways to stop smoking / example ; e.g. tax on cigarettes / nicotine patches / E-cigarettes smoking bans ; exercise finance use of / build more, activity centres / AW ; encourage, greater activity / exercise ; medical idea of, check-ups / screening population (at risk of heart disease / high blood pressure / high cholesterol) ; provide / subsidise, drugs to, reduce blood pressure / lower cholesterol ; research funding research into heart disease ; [max 3] [Total: 6]