Cambridge A Level Biology 9700 — 2010 May/June Paper 2 · Variant 3

This document consists of 15 printed pages and 1 blank page. DC (SM/DJ) 25482/3 © UCLES 2010 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level 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 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. 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. * 9 0 7 2 1 4 9 3 6 3 * BIOLOGY 9700/23 Paper 2 Structured Questions AS May/June 2010 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 2 3 4 5 6 Total

2 9700/23/M/J/10 © UCLES 2010 For Examiner’s Use Answer all the questions. 1 Fig. 1.1 shows part of an animal cell viewed with an electron microscope. A B C 6 µm Fig. 1.1 (a) Name the structures A to C. A … B … C …[3] (b) (i) State the function of structure C. …[1] (ii) Explain why structure C cannot be seen using a light microscope. … … … …[2]

3 9700/23/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (c) Suggest one disadvantage of the electron microscope compared to the light microscope for the study of cells. … …[1] (d) Calculate the magnification of the image in Fig. 1.1. Show your working and give your answer to the nearest whole number. Answer = …[2] [Total: 9]

4 9700/23/M/J/10 © UCLES 2010 For Examiner’s Use 2 Fig. 2.1 shows a diagram of a section through a human heart. X Y Z Fig. 2.1 (a) State the name and function of the circled structure labelled X. name … function … … …[3] (b) Explain why the region labelled Y is thicker than the region labelled Z. … … … … … …[3]

5 9700/23/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (c) Cardiac muscle is described as myogenic as it naturally contracts and relaxes. With reference to the structures and tissues within the heart, describe how the cardiac cycle is initiated and coordinated. … … … … … … … … … …[5] [Total: 11]

6 9700/23/M/J/10 © UCLES 2010 3 The amino acid sequence of the protein hormone insulin is shown in Fig. 3.1. Phe polypeptide chain B Val Asn Gln His Leu Cys S S Gly Ser His Leu Val Glu Ala Leu Tyr Leu Val Cys Gly Glu Arg Gly Phe Phe Tyr Thr Pro Lys Thr 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Gly polypeptide chain A Ile Val Glu Gln Cys S Cys Thr Ser Ile Cys Ser Leu Tyr Gln Leu Glu Asn Tyr Cys Asn 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 S S S Fig. 3.1

7 9700/23/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (a) With reference to Fig. 3.1, state (i) which two levels of protein structure are shown 1. … 2. …[2] (ii) the name of the structures responsible for holding the two polypeptide chains together. …[1] (b) Many people with diabetes need to take regular injections of insulin. Insulin in the form shown in Fig. 3.1 cannot be taken by mouth as it would be hydrolysed by proteases in the gut. In the space below, draw a diagram to show how the peptide bond between glutamine 15 and leucine 16 in polypeptide chain A could be hydrolysed and show the products of the hydrolysis. CH3 NH2 CH2 CH3 CH leucine glutamine CH2 C H H N O C rest of chain C H CH2 C H N rest of chain O O C [3] [Total: 6]

8 9700/23/M/J/10 © UCLES 2010 For Examiner’s Use 4 The control of malaria is one of the top priorities of the World Health Organization (WHO). At present, there is no effective vaccine for the disease, so other preventative measures must be taken to control the spread of malaria. (a) Describe one method of controlling the spread of malaria by targeting its vector and explain its effect. … … …[2] (b) Explain why it has been difficult to develop an effective vaccine for malaria. … … … … … … …[3]

9 9700/23/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (c) Another method of preventing malaria is to take drugs, such as chloroquine, but resistance to these drugs among certain species of the malarial parasite is increasing. New drugs are being developed. A laboratory investigation was carried out to determine the effect of a new drug on two strains of the malarial parasite Plasmodium falciparum. The results are shown in Fig. 4.1. 100 chloroquine-sensitive P. falciparum chloroquine-resistant P. falciparum 80 60 40 percentage of parasites killed after 24h 20 0 0 1 2 concentration of new drug / µmol dm–3 3 4 5 Fig. 4.1 With reference to Fig. 4.1, compare the effect of increasing the concentration of the drug on the chloroquine-resistant and chloroquine-sensitive strains of P. falciparum. … … … … … … …[3]

10 9700/23/M/J/10 © UCLES 2010 (d) When a person becomes infected with the Human Immunodeficiency Virus (HIV) they become more susceptible to infection by the malarial parasite. Fig. 4.2 shows maps of Africa produced by the WHO. • Fig. 4.2a shows the percentage population of each country testing positive for HIV • Fig. 4.2b shows the percentage increase in malaria as a result of HIV infection in each country. 20.0% – 28.0% 10.0% – <20.0% 5.0% – <10.0% 1.0% – <5.0% <1.0% No data available Not included in analysis HIV prevalence (%) 50%–110% increase 8%–49% increase 3%–7% increase 0%–2% increase Not included in analysis Malaria prevalence (%) Fig. 4.2a Fig. 4.2b

11 9700/23/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (i) Explain how the information in Fig. 4.2 supports the idea that there is a link between HIV infection and susceptibility to malaria. … … … …[2] (ii) Suggest how HIV infection may have led to an increase in malarial infections in these countries. … … … …[2] [Total: 12]

12 9700/23/M/J/10 © UCLES 2010 For Examiner’s Use 5 (a) Some bacteria, such as Rhizobium, carry out nitrogen fixation, which is an important process in the nitrogen cycle. Explain what is meant by the term nitrogen fixation. … … … …[3] (b) An important enzyme in the nitrogen cycle is urease, which catalyses the hydrolysis of urea to ammonia. This reaction is shown below: urease (NH2)2CO + H2O 2NH3 + CO2 (i) State the name of this process in the nitrogen cycle. …[1] (ii) Explain the importance of this process in making nitrogen from animals available for uptake by plants. … … … …[2]

13 9700/23/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (c) The enzyme urease is known to be affected by competitive inhibitors. A student carried out an investigation to determine the percentage of urea hydrolysed by urease at various time intervals • without any inhibitor • with a competitive inhibitor. The experiment was carried out in test tubes set up as follows: Tube A – 1 cm3 of urease solution, 10 cm3 pH 7.5 buffer solution, 1 cm3 urea solution. Tube B – 1 cm3 urease solution, 9 cm3 pH 7.5 buffer solution, 1 cm3 inhibitor, 1 cm3 urea solution. Tube C – 1 cm3 water, 10 cm3 pH 7.5 buffer solution, 1 cm3 urea solution. The results are shown in the table below. time / min percentage of urea remaining Tube A Tube B Tube C 0 100 100 100 5 55 99 100 10 29 98 100 15 14 96 100 20 8 95 100 25 5 92 100 30 3 90 100 (i) State how Tube C acts as a control for this investigation. … …[1] (ii) Explain the difference in results between Tube A and Tube B. … … … … … … …[4] [Total: 11]

14 9700/23/M/J/10 © UCLES 2010 For Examiner’s Use 6 Various structures in the human gas exchange system are adapted in different ways to perform their specific functions. (a) Complete the table below using a tick ✓ or cross ✗ in each box to show whether or not the structure shows the particular feature. Two boxes have been completed for you. lined with cilia reinforced with cartilage site of gas exchange contains smooth muscle trachea ✗ bronchus bronchiole ✓ alveolus [4] (b) State the two ways in which the concentration gradients of oxygen and carbon dioxide are maintained for efficient gas exchange. 1. … … 2. … …[2] (c) The alveoli in the lungs have elastic fibres in their walls. (i) State one function of the elastic fibres. … …[1] (ii) Name the medical condition caused by breakdown of the elastic fibres. …[1]

15 9700/23/M/J/10 © UCLES 2010 For Examiner’s Use (d) Cigarette smoke contains tar, a substance which has several harmful effects on the cells lining the gas exchange system. Outline three of these effects. 1. … … 2. … … 3. … …[3] [Total: 11]

16 9700/23/M/J/10 © UCLES 2010 BLANK PAGE 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.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2010 question paper for the guidance of teachers 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 must be read in conjunction with the question papers and the report on the examination. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the May/June 2010 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 23 © UCLES 2010 1 (a) A nucleus ; A (eu)chromatin R nucleolus B mitochondrion ; A mitochondria C (rough) endoplasmic reticulum ; A (R)ER R smooth/S [3] (b) (i) protein/polypeptide, synthesis/AW ; A protein, transport/modification A ecf if C is identified as Golgi or SERor ribosomes in 1 (a) [1] (ii) ignore refs to magnification resolution/resolving power, low(er) ; ora 200 nm compared to 0.5 nm ; A resolution quoted in range 100-300 to 0.2-1.0 nm ref. to visibility of structure C ; e.gs. wavelength of light longer than size of, ribosomes/membrane ribosomes/membrane, cannot be seen as less than 200nm diameter ribosomes only 20–30 nm diameter A 15–20 nm membranes 7–10 nm thick small size linked to explanation of resolution [2 max] (c) any one relevant disadvantage e.g. only dead specimens can be viewed ; mounted in vacuum/pre-treatment, may distort delicate structures ; A artefacts expensive, qualified ; e.g. to buy, maintain, increased cost electricity, costs associated with, time/training requires, more electrical power ; requires stable, high voltage supplies/currents ; sensitive to external magnetic fields ; difficult to operate/requires technical training ; samples more difficult to prepare ; A examples e.g. thin sections lengthy preparation time ; monochrome/black and white only ; not portable/can only be used in specific locations (e.g. with voltage supplies) ; [1 max] (d) allow +/- 1 mm in reading the line award two marks if correct answer is given 20 000/6 µm = (3333.3) A 19 000/6 = (3 166.7) A 21 000/6 = (3 500.0) 3 333 (x);; A 3 167 (x) A 3 500n(x) award one mark if answer is given to one or more decimal places or award one mark if correctly measured and divided by 6 µm but incorrectly converted [2 max] [Total: 9]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 23 © UCLES 2010 2 (a) semilunar valve ; A pulmonary valve prevents backflow (of blood) ; from the pulmonary artery/into the right ventricle ; or ensures one-way flow of blood ; from the right ventricle/into the pulmonary artery ; [3] (b) (Y/wall of left ventricle) contains more (cardiac) muscle ; ora left ventricle/ventricle beside Y, pumps blood to, whole body / further ; ora at higher pressure with more force (than right) ; ora resistance to blood flow is greater in systemic circulation ; ora [3 max] (c) any two of SAN, AVN, Purkyne tissue/Bundle of His in correct context ; SAN/(primary) pacemaker, sends out, waves of excitation/impulses ; A electrical (im)pulses R once only nervous impulse(s)/pulse(s)/signal(s) R if brain stimulates SAN to send out impulses spreads across atria ; atria contract/atrial systole ; fibrous ring/non-conducting tissue/insulating tissue ; prevents, it reaching the ventricles/ventricles contracting at the same time (as atria); atrio-ventricular node/AVN, acts as ‘relay station’/sends wave of excitation to ventricles; A in correct context – impulse reaches AVN and is passed on (therefore) time delay to allow, atria to empty/atria to complete contraction/ventricles to fill// atria and ventricles do not contract at the same time ; time ref. 0.1 – 0.2 seconds ; Purkyne tissue bundle of His, conducts, excitation/impulses, to base of, septum/ventricles ; A apex of heart spreads upwards in ventricle (walls) ; (so) ventricles contract from base upwards/ventricles force blood up from base ; [5 max] [Total: 11]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 23 © UCLES 2010 3 (a) (i) primary ; A first quarternary ; A fourth [2] (ii) disulfide (bonds/bridges) ; [1] (b) peptide bond broken ; correct involvement of water ; free –COOH/–COO- and free –NH2/–NH3 + shown ; [3] [Total: 6] 4 (a) any one correct description (1 mark) with explanation (1 mark) e.g. any named biological control method e.g B. thuringiensis ; kills mosquito larvae ; use of insecticides ; kills (adult) mosquitoes ; elimination of standing water ; removes, mosquito breeding sites/egg-laying areas ; use of oil on water ; prevents maturation of/kills, mosquito larvae ; [2 max] (b) (malarial) parasite/pathogen/Plasmodium, has many antigens ; eukaryotic/many genes ; many different stages of life cycle ; ref. to more than one Plasmodium species/strain of each species ; mutation changes antigens (over time)/antigenic shift/antigenic drift ; parasite only vulnerable, at certain stages of life cycle/when free in plasma ; antigenic concealment/described ; AVP ; e.g. changes antigens which are expressed (through gene switching) [3 max] (c) percentage of, parasites killed/growth inhibition, increases with drug concentration for both parasites ; effect is greater on chloroquine-resistant parasites/AW ; chloroquine-sensitive parasites not affected until 1 µmol dm-3 ; further use of data from Fig. 4.1 to illustrate ; further detail of difference in trend(s) ; A descriptive or figures [3 max]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 23 © UCLES 2010 (d) (i) (percentage) increase in malaria is high(er) in, countries in the, south/south and east ; ora A named countries R more malaria ref. (percentage) increase correlates with countries where HIV incidence is higher ; penalise once if no ref to increase data quote ; [2 max] (ii) HIV, infects/AW, T (helper)–lymphocytes/T-cells ; qualified ref. to immune system ; (HIV and) malaria may be contracted via blood transfusion ; ref. to reduced number of workers so malaria prevention not carried out ; [2 max] [Total: 12] 5 (a) conversion of/AW, nitrogen (gas)/N2 ; in context of atmospheric nitrogen (to) ammonium (ions/compounds)/NH4 +/amino acids ; further detail ; e.g. nitrogenase (enzyme)/ref. conversion from unreactive (nitrogen) to reactive (compound)/reduction of nitrogen/ATP required/anaerobic conditions required for enzyme function [3] (b) (i) ammonification/putrefaction/decomposition/decay ; [1] (ii) supplies, ammonia/ammonium ions, for, nitrifying bacteria/nitrification ; ammonia/ammonium ions, converted/oxidised/AW ; to nitrite ; to nitrate ; Nitrosomonas/Nitrobacter ; in correct context ref. nitrate useable form for plants ; [2 max] (c) (i) to check that urea is not hydrolysed/broken down, without enzyme ; ora A there is no reaction without enzyme [1] (ii) hydrolysis reduces, substrate/urea, concentration ; urea, hydrolysed/broken down, more quickly in Tube A than in Tube B; A ref. to differences in reaction rates Tube A enzyme can bind with substrate normally/ES complexes forming (at fast rate) ; ora Tube B shape of active site complementary to (shape of) substrate/AW ; Tube B (competitive) inhibitor, occupying/binding at/AW, active site ; ref. substrate unable to enter active site/AW ; correct data quote from either column to illustrate ; [4 max] [Total: 11]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 23 © UCLES 2010 6 (a) 1 mark each correct row lined with cilia reinforced with cartilage site of gas exchange contains smooth muscle trachea


; bronchus


; bronchiole
  ; alveoli  
 ; [4] (b) good/circulating, blood supply ; good ventilation/breathing movements ; [2] (c) (i) stretch/expand/lengthen, on inspiration and, recoil/shorten, on expiration ; A alternatives for inspiration and expiration R contract and relax (stretch) to increase, surface area/volume of air, for, diffusion/gas exchange ; (recoil) to help, expel air/force air out ; ignore contract prevent alveoli, bursting/breaking/AW ; R collapsing [1 max] (ii) emphysema ; [1] (d) (cause) mutations ; uncontrollable, division/mitosis/cell replication/cell growth ; lack of contact inhibition/no apoptosis or described/(proto)oncogenes ; goblet cells secrete, excess/more/AW, mucus ; destroys/weakens/paralyses/AW, cilia ; development of scar tissue ; inflammation ; increased chance of infection/AW ; [3 max] [Total: 11]