Cambridge A Level Biology 9700 — 2013 Oct/Nov Paper 2 · Variant 1

This document consists of 15 printed pages and 1 blank page. DC (LEG/SW) 63266/2 © UCLES 2013 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level * 8 8 0 5 7 5 9 0 2 6 * BIOLOGY 9700/21 Paper 2 Structured Questions AS October/November 2013 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 ink. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. 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/O/N/13 © UCLES 2013 For Examiner’s Use Answer all the questions. 1 Fig. 1.1 shows a cell of a female fruit fly, Drosophila melanogaster, during a stage of mitosis. W X Y Fig. 1.1 (a) (i) Name the stage of mitosis shown in Fig. 1.1. …[1] (ii) Shade a pair of homologous chromosomes. [1] (iii) Name the structure labelled W and state its function. … … …[2]

3 9700/21/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) State what happens to structure X and to structure Y between the stage shown in Fig. 1.1 and the end of cell division. … … … … … … … …[3] [Total: 7]

4 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use 2 (a) Table 2.1 shows eight ions that are biologically important. Table 2.1 ammonium (NH4 +) A hydrogen (H+) B hydrogen carbonate (HCO3 –) C iron (Fe2+) D magnesium (Mg2+) E nitrate (NO3 –) F phosphate (PO4 3–) G sulfate (SO4 2–) H Choose one ion to match each of the following statements. In each case write one letter from Table 2.1. You may use each letter (A to H) once, more than once or not at all. (i) A component of polynucleotides. …[1] (ii) Ion produced by enzyme activity inside red blood cells. …[1] (iii) Ion used in the production of all amino acids in chloroplasts. …[1] (iv) Ion that diffuses through carrier proteins with sucrose into companion cells in phloem tissue. …[1] (v) Component of haem group in haemoglobin that binds oxygen. …[1]

5 9700/21/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) The enzyme nitrogenase is found in free-living and symbiotic nitrogen-fixing bacteria. Nitrogenase catalyses the reaction: N2 (g) + 6 e– + 8H+ (aq) 2NH4 + (aq) Some nitrogenase enzymes have vanadium ions in their active sites; others have molybdenum ions. Explain how the enzyme nitrogenase functions in the fixation of nitrogen. … … … … … … … … …[4]

6 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use (c) Some pea plants were grown with their roots in a solution of mineral ions. The solution was kept aerated for three days. The concentrations of five ions in the solution and in the root tissue were determined after the three days. The results are shown in Table 2.2. Table 2.2 ion concentration / mmol dm–3 surrounding solution root tissue potassium (K+) 1.0 75.0 magnesium (Mg2+) 0.3 3.5 calcium (Ca2+) 1.0 2.0 phosphate (PO4 3–) 1.0 21.1 sulfate (SO4 2–) 0.3 19.7 With reference to Table 2.2, suggest how cell surface membranes of root cells are responsible for the concentrations of ions in the roots compared to the surrounding solution. … … … … … … … … … … … … …[5] [Total: 14]

7 9700/21/O/N/13 © UCLES 2013 [Turn over Question 3 starts on page 8

8 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use 3 (a) Tuberculosis (TB) and chronic obstructive pulmonary disease (COPD) are diseases that affect the lungs. With reference to TB and COPD, explain how infectious diseases differ from non-infectious diseases. … … … … …[2] Macrophages are large phagocytic cells that are found in many tissues including alveolar tissue in the lungs. They provide the main means of defence against pathogens in this tissue. Fig. 3.1 is a drawing made from an electron micrograph showing part of a capillary and two alveoli, with a macrophage. macrophage Fig. 3.1

9 9700/21/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) With reference to Fig. 3.1, explain: (i) how alveoli are adapted for gaseous exchange … … … … … …[3] (ii) how macrophages function to protect the lungs from becoming infected. … … … … … … … …[4] (c) Phagocytes release enzymes that digest proteins. In smokers, this may lead to the large-scale destruction of alveolar walls. Outline the effects of this destruction on a person’s health. … … … … … …[3] [Total: 12]

10 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use 4 Cholesterol is synthesised in the smooth endoplasmic reticulum (SER) in liver cells by a series of enzyme-catalysed reactions. Within the SER, molecules of cholesterol and triglycerides are surrounded by proteins and phospholipids to form lipoproteins. These lipoprotein particles enter the Golgi apparatus where they are packaged into vesicles and pass to the blood. Fig. 4.1 is an electron micrograph of part of a liver cell showing lipoprotein particles within the Golgi apparatus. lipoprotein particle T membrane- bound duct Fig. 4.1 (a) Name structure T in Fig. 4.1 and state its role in liver cells. … … … … … …[3]

11 9700/21/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) (i) Suggest why cholesterol is packaged into lipoproteins before release from liver cells into the blood. … … … …[1] (ii) Explain why cells of the body need to be supplied with cholesterol. … … … … …[2] (c) Cholesterol is also packaged into vesicles by the SER and then secreted from the cell into small fluid-filled spaces between the liver cells. These spaces form ducts that drain into the gall bladder to form bile. Suggest how cholesterol is secreted into ducts, such as the duct in Fig. 4.1. … … … … …[2] (d) State one function of the Golgi apparatus other than the packaging of substances into vesicles for transport. … …[1] [Total: 9]

12 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use 5 Table 5.1 shows the triplets of bases on the template polynucleotide of DNA for some amino acids. Table 5.1 amino acid DNA triplets glutamic acid (glu) CTT CTC histidine (his) GTA GTG leucine (leu) GAA GAG GAT GAC proline (pro) GGA GGG GGT GGC threonine (thr) TGA TGG TGT TGC valine (val) CAA CAG CAT CAC Fig. 5.1 shows the base sequences in DNA and mRNA for the first seven amino acids of the β chain of haemoglobin. DNA CAC … GAC TGA GGA CTC CTC mRNA GUG CAC CUG … CCU GAG GAG β chain val his … thr pro glu glu Fig. 5.1 (a) (i) Use Table 5.1 to complete Fig. 5.1. [3] (ii) State the term used to describe the sequence of amino acids in a polypeptide. …[1]

13 9700/21/O/N/13 © UCLES 2013 [Turn over For Examiner’s Use (b) In sickle cell anaemia, the amino acid at position 6 in the β chain is valine and not glutamic acid. Explain how a single change in the DNA triplet for the sixth amino acid of the gene coding for the β chain leads to the production of a different amino acid sequence. … … … … … … … … … … … …[5] [Total: 9]

14 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use 6 In some ecosystems, certain species fulfil important roles in maintaining biodiversity in communities. These species are often known as keystone species. The sea otter, Enhydra lutris, is found in waters of the northern and eastern coasts of the Pacific, where it occupies a niche as a predator. These coastal waters are rich in kelp communities. Kelp are very large seaweeds that form ‘underwater forests’. In the 19th century the sea otter was hunted for its fur, with the result that populations decreased. A consequence of this reduction in numbers was the disappearance of much of the kelp. Conservation measures in the 20th century restored the numbers of sea otters. Fig. 6.1 shows the food web for this ecosystem. sharks sea otters large carnivorous fish starfish (sea stars) abalones large crabs small carnivorous fish and invertebrates scallops and sessile invertebrates microscopic floating animals detritus kelp (very large seaweeds) smaller seaweed phytoplankton small herbivorous invertebrates small herbivorous fish sea urchins Fig. 6.1

15 9700/21/O/N/13 © UCLES 2013 For Examiner’s Use (a) Explain the meaning of the terms niche and community. niche … … … … community … … … …[2] (b) With reference to the food web in Fig. 6.1, suggest why sea otters are considered to be a keystone species. … … … … … … … … … …[4] (c) Suggest how the efficiency of energy transfer from kelp to sea urchins could be determined. … … … … … … …[3] [Total: 9]

16 9700/21/O/N/13 © UCLES 2013 Copyright Acknowledgements: Fig. 4.1 © DON W. FAWCETT/SCIENCE PHOTO LIBRARY. 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. University of 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. BLANK PAGE

CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2013 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 October/November 2013 series for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.

Page 2 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 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 excepted) 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

Page 3 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 1 (a) (i) prophase ; R prophase I [1] (iii) two homologous chromosomes shaded ; [1] (iii) centriole ; A centrosome / microtubule organising centre / MTOC one from produces spindle / produces spindle fibres ; produce / organises, microtubules ; disassembles / AW, spindle / spindle fibres / microtubules ; [max 2] A one e.g. of role of, spindle fibres / microtubules if a link to centriole has been made allow if centriole incorrectly named or if not given (b) max 2 if no attempt made at both X and Y X / cell surface membrane 1 forms a (cleavage) furrow ; A ‘pinches in’ / constricts / AW 2 ref. fusion ; 3 to divide cell into two ; A idea of formation of two (separate) cells linked to behaviour of (cell surface) membrane; 4 ref. to cytokinesis / contractile ring ; Y / nuclear envelope 5 disassembles / breaks down / AW ; 6 during prophase / by end of prophase / before metaphase ; A by the end of prometaphase 7 re-forms / AW, during telophase (from ER) ; [max 3] [Total: 7]

Page 4 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 2 (a) (i) G ; [1] (ii) B / C ; [1] (iii) A / F ; [1] (iv) B ; [1] (v) D ; [1] (b) 1 nitrogen and hydrogen / substrates, bind to / AW, active site ; 2 enzyme-substrate complex (forms) ; 3 ref. lock and key / induced fit, mechanism ; 4 activation energy of reaction is lowered ; 5 example of how activation energy lowered ; e.g. strain on (triple) bond of, N2 / (di)nitrogen A bond broken between nitrogen (atoms) nitrogen and hydrogen ions held close together for bond formation transfer of electrons alternative pathway 6 product / NH4 +, leaves active site ; 7 ATP, required / used / provided from respiration ; 8 ref. anaerobic conditions for enzyme action ; 9 suggestion as to use of, vanadium / molybdenum, in active site ; e.g. act as cofactor / coenzyme transfer of, electrons / protons [max 4]

Page 5 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 (c) 1 concentration of all the ions is greater in the root tissue than in the solution ; ora A roots 2 comparative data quote ; according to these data 3 (so) ions will not diffuse into the root tissue ; A if (facilitated) diffusion only, initially / till equilibrium reached 4 (so) active transport ; A active, uptake / pumping I facilitated diffusion 5 use ATP ; A energy R ATP energy 6 move ions, against concentration gradient / from low to high concentration; A diffusion gradient 7 use, membrane / integral / intrinsic / transmembrane / transport / carrier, proteins ; R channel proteins 8 are specific / have specific binding sites ; 9 involve, conformational / shape, change ; 10 comparative data quote to suggest that some ions are pumped more than others ; e.g. steepest gradients for K+ and SO 4 – 11 phospholipid bilayer / hydrophobic core (of cell surface membrane) is impermeable to ions ; 12 so ions cannot diffuse out / (membrane) proteins only allow inward flow of ions ; 13 AVP ; e.g. suggestion of differing numbers of specific membrane proteins to explain observation of mp 10 [max 5] [Total: 14]

Page 6 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 3 (a) max 1 if no ref. to TB and COPD or if correct definitions given and ref. to TB/COPD incorrect (TB is an infectious disease, COPD non-infectious) TB caused by, a pathogen / Mycobacterium / M. tuberculosis / M. Bovis ; ora for COPD A microorganism / bacterium / bacteria I virus / fungus / protoctist A infectious disease is caused by a pathogen ora TB is / COPD is not, transmissible / communicable / can be passed from one organism to another ; allow detail of TB transmission e.g. droplet infection / in contaminated milk A infectious disease is transmissible ora COPD caused by, damage to / irritation of, lung tissue ; AW accept relevant ref. to tobacco smoking [2] (b) (i) 1 lining / epithelium / wall, is thin / one cell thick / squamous ; I thin interstitium R cell walls of alveoli R alveoli are one cell thick R endothelium / membrane 2 (so) short diffusion distance / only diffuse through two cells ; 3 (collectively / many, so) large surface area for diffusion ; R an alveolus has a large surface area I high SA:V ratio / increase SA 4 surrounded by / many / network of, capillaries ; I good blood supply 5 red blood cells are very close to air (in alveoli) ; 6 (so) maintain, diffusion / concentration / partial pressure, gradient(s) ; 7 elastin / elastic fibres, allow(s) alveoli to, increase in volume / expand / stretch / stop bursting / recoil ; I alveoli are elastic R contract [max 3]

Page 7 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 (ii) allow microorganisms or named type of microorganism or infectious agent for pathogens 1 recognise, non-self / foreign, antigens, (on pathogen) ; 2 receptors (on macrophage) bind antigens (on pathogen) ; 3 (or), pathogen / AW, adheres / ‘sticks’, to (cell surface) membrane ; 4 infolding of (macrophage cell surface) membrane around / engulf / phagocytosis of, pathogen ; R engulf antigen 5 vacuole / vesicle / phagosome, forms ; 6 ref. to lysosomes ; 7 hydrolytic / digestive / named, enzymes ; e.g. lysozyme / protease / nuclease A pathogen broken down by enzymes 8 hydrolysis of named compound(s) ; 9 ref. to destroying / killing, pathogen ; 10 ref. to antigen presentation ; accept idea even though does not occur in alveoli [max 4] (c) 1 emphysema ; 2 (alveolar walls broken down so) less surface area for, gas exchange / diffusion ; A impaired / AW, gas exchange / diffusion 3 difficulty in breathing / restriction in air flow / shortness of breath wheezing / rapid breathing ; 4 blood is less well oxygenated / less oxygen reaches, tissues / muscles ; 5 any two other, signs / symptoms ;; 6 e.g. lethargy / tiredness / fatigue / constraints on mobility or activity wheezing persistent / AW, coughing chest tightness ; R chest pain more prone to / frequent, chest / respiratory, infections A more frequent colds / influenza (‘flu) weight loss swollen, ankles / feet increase in thickness of, right ventricle / right side of heart increase in blood pressure in pulmonary artery [max 3] [Total: 12]

Page 8 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 4 (a) 1 mitochondrion ; A mitochondria A outer mitochondrial membrane 2 produces / synthesises / AW, ATP ; A release / supply, ATP / energy R produces energy R ATP energy or for outer mitochondrial membrane allows exit of (synthesised) ATP to cell 3 example of use of ATP in liver cells ; e.g. for synthesis of, cholesterol / glycogen / protein / biological molecules / polymers / AW intracellular movement of vesicles exocytosis / endocytosis / bulk transport active transport [3] (b) (i) lipoproteins are soluble ; cholesterol is not water-soluble ; cholesterol surrounded by / lipoproteins have, phospholipid heads / proteins, that are hydrophilic ; AW allows transport in blood ; [max 1] (ii) cholesterol needed for making / components of, membranes ; membrane stability ; regulating the fluidity of, membranes / phospholipid bilayer ; production of, steroid hormones / named steroid hormone ; AVP ; e.g. helps prevent entry of, ions / polar molecules [max 2] (c) vesicles travel to cell surface membrane ; A travels through cytoplasm towards space between cells exocytosis ; vesicle / membrane, fusion (with cell surface membrane) ; contents / cholesterol, released ; [max 2] (d) glycosylation / adding sugar molecules to proteins / making glycoproteins ; A modifying proteins phosphorylating proteins ; cutting / folding, proteins ; assembly of polypeptides into proteins (with quaternary structure) ; AVP ; e.g. lipid synthesis ref. lysosome formation [max 1] [Total: 9]

Page 9 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 5 (a) (i) GTG ; ACU ; leu ; [3] (ii) primary structure ; [1] (b) 1 mutation ; 2 base substitution / T
A in template strand of DNA / AW ; transcription 3 DNA has CAC as 6th triplet ; 4 (so) mRNA has GUG as (6th) codon ; allow one mark for altered mRNA codon if no marks gained for mps 3 and 4 translation 5 different tRNA involved / tRNA specific to val and not glu ; 6 anticodon on tRNA has CAC (with valine) ; 7 tRNA brings, incorrect amino acid / val, to ribosome ; 8 further detail ; e.g. incorrect amino acid incorporated into growing polypeptide chain [max 5] [Total: 9]

Page 10 Mark Scheme Syllabus Paper GCE AS/A LEVEL – October/November 2013 9700 21 © Cambridge International Examinations 2013 6 (a) niche functional role / function / role / AW, of a species within an ecosystem ; A population / organism, for species accept description community all populations of all species / all organisms / AW, living in a (particular) area / AW, (at the same time) ; [2] (b) 1 changing / increasing / decreasing, numbers of sea otters has (large) effect on the rest of the ecosystem ; effect on kelp 2 prey on sea urchins, which, graze / feed on, kelp ; 3 if, no / few, otters numbers of urchins increase, so kelp decreases ; ora 4 sea urchins have no other predator ; role of kelp 5 kelp, is a producer / initial input of energy into ecosystem ; 6 so less kelp means less energy available for the ecosystem ; 7 kelp provides habitats for many other species ; 8 loss of kelp (significantly), changes structure of ecosystem / ref. to ‘deforestation’ ; effect on other organisms 9 decrease in numbers (of sea otters) leads (initially) to increase in numbers of their prey / named organism from Fig. 6.1; ora 10 for any one example ref. to consequence / knock-on effect ; 11 AVP ; e.g. ref. to effect on, energy flow through ecosystem / regulation of populations within the ecosystem / community structure [max 4] (c) 1 (determine) energy content of consumed kelp, absorbed / that can be used, by sea urchins ; AW 2 (determine) energy content of kelp consumed by sea urchins ; allow other reasonable suggestions for mps 1 and 2 3 idea of comparing energy contents and expressing as a, percentage / proportion / ratio ; A equation or worded e.g. mp 1 divided by mp 2 4 (calculated as) per unit, area / volume, per unit time ; A example e.g.(J) m–3 year–1 [max 3] [Total: 9]