Cambridge A Level Biology 9700 — 2015 May/June Paper 2 · Variant 1

This document consists of 16 printed pages. DC (ST/JG) 95553/3 © UCLES 2015 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 4 5 4 0 7 5 8 2 6 8 * BIOLOGY 9700/21 Paper 2 Structured Questions AS May/June 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 at the top of the 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 9700/21/M/J/15 © UCLES 2015 Answer all the questions. 1 A student investigated growth in the roots of broad bean, Vicia faba. The student cut sections of the root tip of this plant and viewed them with a light microscope. Fig. 1.1 is a photomicrograph of one of the sections. The cell labelled D is in interphase. H A B C D E F G Fig. 1.1 (a) Complete the table below by: • naming the stages of mitosis in the correct sequence following interphase • identifying one example from the cells labelled A to H that is in each stage of mitosis that you have named. stage of mitosis label from Fig. 1.1 [5]

3 9700/21/M/J/15 © UCLES 2015 [Turn over (b) In animal cells, centrioles are responsible for assembling microtubules to make the spindle at the beginning of mitosis. Describe the role of the spindle during mitosis. … … … … … …[2] (c) State two roles of mitosis in plants and animals other than growth. 1 … 2 …[2]

4 9700/21/M/J/15 © UCLES 2015 (d) V. faba is a legume. Roots of legumes often have swellings at intervals known as nodules. Cells within the nodules contain nitrogen-fixing bacteria. (i) Explain the role of nitrogen fixation in the nitrogen cycle. … … … … … …[2] (ii) Farmers in some parts of the world grow legume crops together with cereal crops in the same field. This is known as intercropping. Explain how intercropping results in an increase in the yield of the cereals when the legumes die. … … … … … … … … …[3] [Total: 14]

5 9700/21/M/J/15 © UCLES 2015 [Turn over 2 Pathogens enter the body in a variety of ways, including through the gas exchange system. The body has several defence mechanisms against the entry of pathogens and their spread throughout the body. Fig. 2.1 is an electron micrograph of a cross section of the lining of a bronchiole. Y X Fig. 2.1 (a) (i) Name tissue X and cell Y. X … Y …[2] (ii) With reference to the structures visible in Fig. 2.1, state three ways in which the lining of the trachea, bronchus and bronchioles provides protection against the entry of bacterial pathogens. 1 … … 2 … … 3 … …[3]

6 9700/21/M/J/15 © UCLES 2015 Fig. 2.2 shows part of the immune response to the first infection by a bacterial pathogen that has entered the body through the lining of a bronchiole. J and K are stages in the immune response. Key antigen bacterium secretion of cytokines J L K cytotoxic T-lymphocyte helper T-lymphocytes B-lymphocytes Fig. 2.2 (b) (i) State what is happening at stage J. … …[1] (ii) Explain the role of cell L at stage K in the immune response. … … … … …[2]

7 9700/21/M/J/15 © UCLES 2015 [Turn over (c) With reference to Fig. 2.2, explain how the response to a second infection by this bacterial pathogen differs from the first. … … … … … … … … …[3] (d) There are various ways in which the effectiveness of immune responses can be reduced. Suggest how each of the following reduces the effectiveness of an immune response. (i) The number of T-lymphocytes is reduced in a person with HIV/AIDS. … …[1] (ii) Some pathogens are covered in cell surface membranes from their host. … …[1] (iii) B-lymphocytes do not mature properly and do not recognise any antigens. … …[1] [Total: 14]

8 9700/21/M/J/15 © UCLES 2015 3 When a leaf is first formed it is described as a sink for carbohydrate. As the leaf continues to grow, it starts to photosynthesise and becomes a source of carbohydrates and other assimilates. Fig. 3.1 shows the changes that occur to the structure of plasmodesmata in the leaf as it grows. middle lamella cell wall two simple plasmodesmata complex (branched) plasmodesmata cell surface membrane cytoplasm Fig. 3.1 (a) Suggest the advantage of complex plasmodesmata between cells in leaves. … … … … …[2]

9 9700/21/M/J/15 © UCLES 2015 [Turn over (b) Assimilates are transported into phloem sieve tubes. Explain how assimilates in phloem sieve tubes move from the veins in a mature leaf to sinks, such as flowers and fruits, in the rest of the plant. … … … … … … … … … …[4] [Total: 6]

10 9700/21/M/J/15 © UCLES 2015 4 (a) Fig. 4.1 shows two ways in which enzymes interact with their substrates. enzyme A substrate enzyme B Fig. 4.1 Explain the difference between the two ways in which enzymes interact with their substrates as shown in Fig. 4.1. … … … … … … …[3]

11 9700/21/M/J/15 © UCLES 2015 [Turn over (b) Carbonic anhydrase is an enzyme that is found in blood, liver and kidneys. Fig. 4.2 shows a molecular model of this enzyme. Q P Fig. 4.2 (i) With reference to Fig. 4.2 and the parts labelled P and Q, explain the term secondary structure. … … … … … … …[3] (ii) Describe the role of carbonic anhydrase in the blood. … … … … … … … …[4] [Total: 10]

12 9700/21/M/J/15 © UCLES 2015 5 Fig. 5.1 shows a diagram of the molecular structures of tristearin (a triglyceride) and phosphatidylcholine (a phospholipid). C C C C O O H H tristearin H H H O O C O C O C C C C O O H H H phosphatidylcholine H H H H O O– N+ CH3 CH3 CH3 O H C O O P O C C H Fig. 5.1 (a) Table 5.1 shows a structural difference between the two molecules shown in Fig. 5.1. Complete Table 5.1 with two further structural differences other than in numbers of different types of atoms. Table 5.1 structural feature tristearin phosphatidylcholine length of fatty acid chains all the same length different lengths [2]

13 9700/21/M/J/15 © UCLES 2015 [Turn over (b) Cells in the pancreas secrete enzymes, such as amylase and trypsin, into a duct. The enzymes are packaged in vesicles so that they can be exported from these cells as shown in Fig. 5.2. enzymes plasma membrane cytoplasm Fig. 5.2 With reference to Fig. 5.2, explain how enzymes that are secreted by cells in the pancreas are packaged into vesicles and exported. … … … … … … … … …[4]

14 9700/21/M/J/15 © UCLES 2015 (c) Water has many significant roles to play in cells and living organisms. Complete Table 5.2 below by stating the property of water that allows each of the following to take place. Table 5.2 role of water property of water solvent for glucose and ions movement in xylem helps to decrease body temperature in mammals [3] [Total: 9]

15 9700/21/M/J/15 © UCLES 2015 [Turn over 6 Red blood cells are formed from cells called reticulocytes. Stem cells in the bone marrow produce reticulocytes which differentiate into red blood cells. During differentiation haemoglobin is produced. Fig. 6.1 shows the structure of small sections of DNA and messenger RNA (mRNA) in the nucleus of a reticulocyte during transcription. O O O O O O O P –O O O O N N HN N N N N N N NH2 O O P –O O O O O O P –O O O O O P –O NH2 O H2N HN O O O O– O P N O O O– O P O O O O O– O P O O N N N NH N N NH2 H2N H2N O N N N N O N O O O O– O P NH P S Q R O O O O P –O O O N N N N NH2 NH2 O O P –O O O OH OH O OH O O P –O O O OH O O P –O NH2 O N O N N NH N O N O NH adenine 3' 3' 3' 5' 5' 5' Fig. 6.1 (a) Name the bases P to S. P … Q … R … S …[4]

16 9700/21/M/J/15 © UCLES 2015 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. (b) Describe the role of the mRNA molecule shown in Fig. 6.1. … … … … … … …[3] [Total: 7]

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the May/June 2015 series 9700 BIOLOGY 9700/21 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 May/June 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 – May/June 2015 9700 21 © Cambridge International Examinations 2015 Mark scheme abbreviations: ; separates marking points / alternatives answers for the same point R reject A accept (for answers correctly cued by the question, or 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 ecf error carried forward I ignore mp marking point (with relevant number)

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 1 (a) one mark for the stages of the cell cycle in the correct sequence one mark for correct matching of each stage with a cell stage of mitosis label from Fig. 1.1 prophase A / H ; metaphase G ; anaphase C / E / F ; telophase ; B ; [5] (b) microtubules / spindle (fibres), attach to centromere / kinetochore (of chromosome during prophase) ; I metaphase arranging / aligning / orienting / AW, chromosomes at the equator / metaphase plate ; R centre fibres, shorten / contract / retract ; A microtubules disassemble / AW move / pull, (sister) chromatids / (daughter) chromosomes, to opposite poles / centrioles ; idea that equal number of chromosomes in each daughter, nucleus / cell ; [max 2] (c) maintaining number of chromosomes ; ensuring genetic stability / maintaining genetically identical cells / AW ; asexual reproduction ; A vegetative reproduction / cloning cloning / clonal expansion, of (named) lymphocytes ; A B / T cells replacement of (worn out / dead / damaged) cells ; regeneration, of (named) tissues / organs ; (wound) repair (of tissues) ; R repair of cells ref. to production of gametes ; e.g. mitosis in gametogenesis / gamete production in plants R ‘copying of cells’ [max 2]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 (d) (i) accept biological N fixation or Haber-Bosch process for mp1 1 either converts, (inorganic) nitrogen / dinitrogen / N2, into organic nitrogen / ammonia / NH3 / ammonium / NH4 + ; R if nitrate given or lightning converts, nitrogen / ammonia / NH3 / ammonium / NH4 +, into, nitrite / nitrate (ions) ; 2 reduces nitrogen / breaks triple bond ; 3 makes (fixed) nitrogen available to, legumes / other organisms / community / AW ; A ref. to amino acids / proteins not to be awarded if it follows nitrification 4 increase soil fertility ; 5 balances the loss of fixed nitrogen in, denitrification / ocean deposits ; [max 2] (ii) 1 idea of decay / decomposition ; e.g. breakdown by, (saprophytic) bacteria / fungi 2 legumes eaten by, detritivores ; A named detritivores 3 decomposers produce proteases ; 4 to, hydrolyse / convert / change / AW, protein to amino acids ; 5 amino acids are deaminated ; 6 (amino acids) to, ammonia / NH3 / ammonium (ions) / NH4 + ; 7 nitrifying bacteria / Nitrosomonas, convert ammonia to nitrite (ions); 8 nitrifying bacteria / Nitrobacter, convert nitrite to nitrate (ions) ; if mp7 or mp8 not awarded allow one mark for the following as mp9 9 (named) nitrifying bacteria convert, ammonia / ammonium, to nitrate (ions) ; mp10 only to be awarded following nitrification 10 nitrate (ions) used for making, amino acids / proteins (hence increase in growth of cereals) ; [max 2] [Total: 14]

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 2 (a) (i) X – (ciliated) epithelium ; Y – red blood cell / erythrocyte ; [2] (ii) cilia beat to move mucus (up the bronchiole / towards the mouth / away from the lungs / AW) ; mucus as a barrier to entry into (epithelial) cells ; mucus traps, pathogens / bacteria / microbes ; accept in context of goblet cells capillary / blood vessel, brings, phagocytes / macrophages (to engulf bacteria) ; [max 3] (b) (i) J – phagocytosis / endocytosis / described in terms of engulfing or forming phagosome ; [1] (ii) digestion of bacteria / described ; to destroy bacteria / pathogen ; A to prevent spread through the body antigen, presentation / display on cell surface ; idea of selection of specific, B cells / T cells ; A recognition / binding of / activation of, appropriate B / T cells [max 2] (c) 1 faster ; in context of whole secondary response 2 memory cells; in context of production during the first response 3 idea that there are many more cells specific for this pathogen ; 4 (so) increases chances of encountering pathogens more quickly / AW ; 5 fast(er) production of, B lymphocytes / plasma cells / antibodies / helper (T) cells / cytotoxic T cells / cytokines ; 6 greater concentration of antibodies (in, blood / lymph) or greater numbers of, B / plasma, cells ; A more, antibodies / plasma cells / B cells 7 pathogen, removed / killed, faster ; 8 person does not become ill / no symptoms ; A pathogen does not, spread through the body / infect cells / AW [max 3]

Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 (d) (i) little / no / slower / weak, immune response ; stated function of T-lymphocytes, does not occur / occurs slowly ; e.g. release of cytokines / stimulating macrophages / stimulating B cells / killing infected cells high susceptibility to infectious diseases ; R ‘fighting disease’ [max 1] (ii) pathogen not recognised, as non-self / foreign ; pathogen is recognised as self ; A non-foreign ignore antigen concealment [max 1] (iii) no, antibodies / plasma cells / memory (B) cells, produced ; no humoral response ; no antigen presentation by B cells ; [max 1] [Total: 14] 3 (a) increased / faster, movement / diffusion, of, assimilates / amino acids / sucrose / water / solutes / ions / molecules ; I substances / particles / carbohydrates I freely / easily / efficiently I osmosis (because) more, (symplast) pathways / passages / AW ; accept in context of blockage of some plasmodesmata correct ref. to symplast pathway in context of an advantage ; e.g. of complex plasmodesmata ; from companion cell into sieve tube (elements) / when loading sucrose into phloem AVP ; e.g. selectivity / control / regulation, of movement [max 2] (b) 1 mass flow ; A pressure flow 2 sucrose / solutes / assimilates / sugars, decreases, water potential / solute potential ; A symbol(s) Ψ 3 water enters (sieve tubes), down water potential gradient / by osmosis ; 4 increase in / high(er), hydrostatic pressure ; 5 unloading / removal, of sucrose at the sink lowers the (hydrostatic) pressure ; 6 movement (from source to sink) is by gradient in (hydrostatic) pressure ; [max 4] [Total: 6]

Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 4 (a) enzyme A uses ‘lock and key’ and enzyme B uses induced fit ; A enzymes work by ‘lock and key’ and induced fit enzyme A / lock and key, (shape of) active site is complementary / AW, to (shape of) substrate (molecule) ; enzyme B / induced fit, has an active site that, moulds around / AW, the substrate ; [3] (b) (i) 1 P is β-pleated sheet, Q is α-helix ; accept if P and Q are identified by a description 2 determined by, coiling / folding / sequence, of amino acids / polypeptide ; A primary structure for sequence of amino acids 3 stabilised / held / AW, by hydrogen bonds ; 4 between C = O and H–N (of peptide bonds) ; A carbonyl / carboxyl group, and, amine / amino group 5 ref to, parallel / anti-parallel, nature of β-pleated sheet ; [max 3] (ii) 1 catalyses reaction between carbon dioxide and water to form carbonic acid ; A correct, formulae / equation 2 very fast reaction ; 3 in (cytoplasm of) red blood cell / erythrocyte ; 4 (so there are) hydrogen ions / protons, and hydrogencarbonate ions ; 5 hydrogen ions promotes oxyhaemoglobin dissociation / AW ; e.g. reduces affinity of haemoglobin for oxygen / (oxy)haemoglobin gives up oxygen more readily 6 increases supply of oxygen to (respiring) tissues ; 7 carbon dioxide is transported as hydrogencarbonate ions ; 8 in the plasma ; A carbon dioxide diffuses from red blood cell to plasma 9 AVP ; e.g. carbonic anhydrase catalyses reverse reaction in the lungs ref to hydrogencarbonate ions as buffer in plasma (as a consequence of reaction) R buffering action of haemoglobin in red blood cells [max 4] [Total: 10]

Page 8 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 5 (a) structural feature triglyceride phospholipid phosphate (group) / contains phosphorus
 nitrogen
 charged / polar
 (number of) fatty acids 3 2 number of ester bonds 3 2 number of phosphate ester bonds 0 1 award one mark for any of the following comparisons number of double bonds (in hydrocarbon chain) 0 1 number of saturated fatty acids / ORA 3 1 presence of double bonds
 presence of unsaturated fatty acids
 [max 2] (b) answer may be phrased in the context of amylase / trypsin ignore anything before Golgi, e.g. shuttle vesicles from RER 1 vesicles, form from / ‘pinch off’, Golgi (apparatus / body / complex) ; 2 vesicles moves, through cytoplasm / to cell (surface) or plasma membrane ; 3 role of cytoskeleton / microtubules in movement of vesicles ; 4 energy / ATP, is required (movement of vesicles / fusion with membrane) ; 5 vesicle fuses with / AW, cell (surface) / plasma, membrane ; I bind / attach A join / merge / becomes part of 6 exocytosis / vesicle ‘opens up’ so that enzyme molecules are released ; 7 ref to fluid nature of, membranes / phospholipid bilayer, that makes this possible ; [max 4] These are alternatives – award one mark only

Page 9 Mark Scheme Syllabus Paper Cambridge International AS/A Level – May/June 2015 9700 21 © Cambridge International Examinations 2015 (c) role of water property of water solvent for glucose and ions dipolar / polar ; A description of polarity of water transport in the xylem hydrogen bonding ; I cohesion / adhesion helps to decrease body temperature in humans high latent heat of vapourisation / high specific heat (capacity) / high enthalpy heat of vapourisation / lots of energy required for evaporation ; [3] [Total: 9] 6 (a) P – thymine ; R thiamine / thiamin / thyamine Q – cytosine ; R – guanine ; S – uracil ; [4] (b) 1 copy of the, DNA / gene, (coding) for a, polypeptide / globin ; A protein 2 travels from, DNA / nucleus / chromosome, to ribosome ; A mRNA made in nucleus, attached to ribosome so movement is implied 3 for translation / for (haemo)globin production ; 4 mRNA codes for, sequence / order, of amino acids ; A for primary structure 5 idea that (nucleotide / base) sequence is a series of codons ; 6 base pairing / AW, between codon on mRNA and anticodon on tRNA ; e.g. of AW hydrogen bonds between bases examples of base pairing: A–U / C–G R binding between bases [max 3] [Total: 7]