Cambridge A Level Biology 9700 — 2010 May/June Paper 5 · Variant 1

This document consists of 10 printed pages and 2 blank pages. DC (SHW) 00479 5/09 16009/5 © UCLES 2010 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Level READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. 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 both 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. * 0 7 9 0 3 4 2 9 5 3 * BIOLOGY 9700/51 Paper 5 Planning, Analysis and Evaluation May/June 2010 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 2 Total

9700/51/M/J/10 © UCLES 2010 For Examiner’s Use 1 Many plants produce two types of leaves. One type is produced where the leaves develop in full sunlight and are called ‘sun leaves’. The other type is produced where the leaves develop in the shade and are called ‘shade leaves’. A student investigated photosynthesis in both types of leaves using leaf discs. Fig. 1.1 shows the method used by the student to obtain the leaf discs. 1. 2. leaf discs cut using a plastic straw forceps used to place six leaf discs into 0.2 mol dm–3 sodium hydrogen carbonate solution in a syringe barrel Fig. 1.1 The student then carried out the following actions: 3. replaced the plunger into the syringe, turned the syringe upside down and pushed in the plunger to force out all the air 4. placed a finger over the open end of the syringe and pulled down the plunger to create a vacuum 5. tapped the side of the syringe to remove air bubbles 6. repeated actions 3–5 until the leaf discs sank to the bottom of the syringe. 2

3 9700/51/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use The student measured the rate of photosynthesis of discs from both types of leaves to test the hypothesis Leaf discs from shade leaves will photosynthesise at a higher rate in low light intensity than leaf discs from sun leaves. Fig. 1.2 shows the appearance of the leaf discs in the syringe as they photosynthesise. discs rise to the surface of the sodium hydrogen carbonate solution Fig. 1.2 (a) (i) Explain why the leaf discs rise to the surface in the light. … … [1] (ii) Using this method, outline how the student could test the hypothesis. … … … … … … … … … … … … …

4 9700/51/M/J/10 © UCLES 2010 For Examiner’s Use … … … … … … … … … … … … … … … … … … … … … … … … … … … … [7]

5 9700/51/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use Fig. 1.3 shows the results that the student plotted from the investigation. 0 0 x -axis y -axis 500 1000 1500 2000 shade leaves sun leaves Fig. 1.3 (b) (i) Suggest labels for the axes of this graph. x-axis … … y-axis … … [2] (ii) State two ways in which the student’s data support the hypothesis. 1. … … 2. … … [2]

6 9700/51/M/J/10 © UCLES 2010 For Examiner’s Use In a further investigation using these two types of leaves, the student estimated the number of stomata per unit area. Epidermal strips from the lower surface of the leaf were mounted in water and observed under a microscope. The diameter of the field of view was measured using an eyepiece graticule. The actual field of view was calculated using a calibration value from a slide micrometer scale. Diameter of field of view at ×100 magnification = 0.5 mm (c) (i) Calculate the area of the field of view. Use the formula r 2. ( = 22 7 or  = 3.14) Give your answer to one significant figure. … [1] (ii) Table 1.1 shows the results of the stomatal count investigation. Table 1.1 number of stomata visible at ×100 magnification mean number of stomata number of stomata per mm2 sun leaves 21 24 36 24 15 18 27 33 18 24 24± 6 120 shade leaves 36 39 35 42 28 36 34 40 48 32 37± 6 Calculate the mean number of stomata per mm2 for the shade leaves. Show your working below and write your answer in Table 1.1. [2]

7 9700/51/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (iii) State the null hypothesis for a statistical test to find out whether the difference in the number of stomata is significant. … … [1] (iv) Name a statistical test that could be used and give the reason for your answer. … … [2] (d) The results of the statistical test showed that the difference was significant. Suggest one reason why there is a difference in the number of stomata of shade leaves and sun leaves. … … [1] [Total: 19]

8 9700/51/M/J/10 © UCLES 2010 For Examiner’s Use 2 One technique used for studying antigen-antibody reactions is immunodiffusion. Wells are cut into an agar support medium to contain antigens and antibodies. Antibodies and antigens diffuse out of the wells into the agar. If an antigen meets a complementary antibody a reaction occurs causing a band of precipitate to appear. Fig. 2.1 shows the results of an immunodiffusion test with known antigens P and Q and the antibodies to these antigens. P Q precipitation due to reaction between antigen P and antibody P precipitation due to reaction between antigen Q and antibody Q agar support medium in a petri dish antibody P + antibody Q Fig. 2.1 In an investigation, the serum from two test organisms was tested for the presence of antibodies to specific antigens. Both organisms had been previously exposed to both antigens. The serum was placed in wells at the edge of the petri dish and the antigens in a central well. Fig. 2.2 shows the test set-up. 1 2 antigen X + antigen Y serum of test organism 1 serum of test organism 2 Fig. 2.2

9 9700/51/M/J/10 © UCLES 2010 [Turn over For Examiner’s Use (a) (i) Suggest one variable that must be controlled in this procedure. … [1] (ii) State the independent variable in this investigation. … [1] (iii) Both test organisms had antibodies against antigen X, but only organism 2 had antibodies against antigen Y. On Fig. 2.2 draw lines to represent where precipitation might have occurred for both organisms. [2] (b) Suggest two disadvantages of immunodiffusion for detecting antigens. 1. … … 2. … … [2]

10 9700/51/M/J/10 © UCLES 2010 For Examiner’s Use (c) A naturally occurring mutant of Plasmodium sp. has been tested for use as a ‘whole organism’ vaccination against malaria. The mutant organism develops normally in mosquito vectors and infects the salivary glands in the same way as non-mutant wild type Plasmodium sp. In mice, the mutant infects liver cells but does not multiply and cannot enter red blood cells. Trials using mice were carried out and the effectiveness of the mutant organism as a vaccine tested by injecting non-mutant wild type Plasmodium sp. into vaccinated and non-vaccinated mice. Table 2.1 shows the results of investigations in mice using the mutant Plasmodium sp. Table 2.1 number of mutant Plasmodium cells given to the mice percentage of mice not infected by wild type Plasmodium sp. test group first inoculation first booster inoculation second booster inoculation 1 0 0 0 0 2 50 000 25 000 25 000 100 3 10 000 10 000 10 000 100 4 10 000 10 000 0 70 (i) Suggest the purpose of including each of the following test groups. group 1 … … groups 2 and 3 … … group 4 … … [3] (ii) Using the information in the question, outline a procedure that might be used to obtain mutant Plasmodium sp. to use in the vaccination trials. … … … … [2] [Total: 11]

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12 9700/51/M/J/10 © UCLES 2010 BLANK PAGE Copyright Acknowledgements: Figure 1.2 © Appearance of leaf discs in a syringe; http://www-saps.plantsci.cam.ac.uk/worksheets/scotland/sunshade.htm Figure 2.1 © W R Clark; The Experimental Foundations of Modern Immunology; 4th Ed; Wiley & Sons Inc; 1991. 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 9700/51 Paper 5 (Planning, Analysis and Evaluation), maximum raw mark 30 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 51 © UCLES 2010 Mark schemes abbreviations:
; separates marking points
/ alternative answers for the same point
R reject
A accept (for answers correctly cued by the question, or guidance for examiners)
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

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 51 © UCLES 2010 Question Expected answer Extra guidance Mark AO 1 (a) (i) oxygen / gas / air, produced (by photosynthesis); Do not allow: use / production of carbon dioxide / respiration / bubbles Allow: losing / releasing oxygen, etc. [1] M (ii) 7 of: independent variable 1. a method of varying light intensity or use low light intensity; 2. ref. to a method of measuring light intensity; 3. ref. to a method of eliminating other light sources; 4. ref. to testing leaf discs for the two locations separately; dependent variable 5. ref. to a method of measuring photosynthesis by rising of discs; 6. ref to time taken; standardising variables (max 3) 7. ref. to discs from more than one leaf (from each location); 8. ref. leaf discs all being same diameter / size / number / mass. 9. ref. to same volume of hydrogen carbonate solution (in syringe); 10. ref. to using fresh hydrogen carbonate solution for each measurement / same concentration of H carbonate; 1. e.g. lamp (with standard bulb) and vary distance / lamp at same distance and vary wattage / lamp at same distance and use filters of different thickness / AW 2. e.g. (light) meter / photodiode / light dependent resistor / photometer / low wattage / 60 or below Allow ref. to using a camera meter 3. e.g. dark room or box for measurement 4. often implied 5. Do not allow: counting bubbles / leaves rising 6. e.g. time for (all or a specified number of) discs to rise / specified time and count the number of discs floating / distance risen in stated time Allow: ecf time for bubble counting 8. Allow: use same straw for cutting 9/10 Watch for confusion with hydrogen carbonate indicator – but ecf

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 51 © UCLES 2010 Question Expected answer Extra guidance Mark AO 11. ref. to method of standardising temperature; 12. ref. to acclimatising before measuring; Reliability 13. ref. to repeating at least three times and taking mean; safety: 14. ref. to low risk investigation / AW or any suitable safety concern + precaution; 11. water bath / incubator / controlled room Do not allow: room temp Do not allow: pH for standardising variables 13. Allow: several or many Allow: to remove anomalies / outliers 14. e.g. hydrogen carbonate + gloves / eye protection dry hands to prevent electrical shock / AW Do not allow: be careful unqualified Do not allow: care with cutting [7] M (b) (i) x – light intensity y – rate of photosynthesis; suitable unit on one axis; Ignore other units light – e.g. arbitrary / lux / lumens / candela / 1/d2 allow, watts / kilowatts / voltage photosynthesis. e.g. 1/time / arbitrary Allow: ecf for unit mark if axes wrong [2] D (ii) (rate of) photosynthesis / gas production / oxygen production for shade leaf (discs) is higher (than exposed discs) at low intensity / ref. figures; photosynthesis / gas production / oxygen production begins at lower light intensity in shade leaf discs; Allow: at high(er) light intensity shade leaves level off / AW, whilst sun leaves continue to rise / AW; Allow: reverse arguments for sun leaves at low intensity Ignore: ‘initial’ if the answer is about rate Do not allow: answers that imply time e.g. starts sooner / before …. Ignore: idea that photosynthesis stops at higher light intensities assume that ‘it’ or ‘they’ is the shade leaves if not stated in the answer [2] E

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 51 © UCLES 2010 (c) (i) 0.2mm2; must have units. [1] D (ii) 185;; two marks if some working shown look for working if answer wrong if 0.196… used ecf and take 188 or 189 – whole nos. only if other values in (c) (i) ecf by checking the calculation 0.2 37 = 185 1/0.2 = 5 5 × 37 = 185 If calculation correct but answer not transferred to table allow both marks [2] D (iii) there is no difference in the, number / frequency, of stomata in, exposed / sun, leaves and, shaded / shade, leaves; Allow: any variation on the basic idea e.g. the (observed) means / number, are the same there is no difference (between the two leaf types) Do not allow: the experimental hypothesis [1] D (iv) t-test; comparing two means / means have a similar standard deviation / data has a normal distribution / is continuous / is not discrete; Do not allow: 2 sets of data are being compared ecf if the test name is incorrect Allow: a correct reason for the t-test. [2] D (d) 1 of: sun leaves have (fewer stomata) as more likely to lose water / transpire; ora shade leaves have (more stomata) to increase gas / CO2 diffusion / AW; Do not allow: to increase photosynthesis unqualified Do not allow: – stomata related to light absorption Watch out for statements that there are more stomata in sun leaves without any qualification. Assume comment applies to shade leaves if not stated. Do not allow: oxygen is given out [1] C Total: [19]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 51 © UCLES 2010 2 (a) (i) 1 of: ref. to thickness / volume / consistency / concentration of, agar / depth of wells / volume of wells / distance of antigen wells from test organism wells; ref to temperature; ref. to volume serum / antigen volume; Do not allow: amount for any quantitative answer Do not allow: pH [1] P (ii) the serum / antibody / antibodies (from the test organisms); Do not allow: if antigen also mentioned Allow: organism from which serum / antibody came Ignore amount / volume etc. [1] P (iii) 2 lines / 1 thick line, between 2 and antigens; 1 line between 1 and antigens; Allow: 2 marks if lines do not intersect If the lines are reversed / spread outside dish max. 1 Do not allow: if the lines are inverted / lines cross wells [2] C (b) 2 of: 1. ref. to all antibodies not forming precipitates / AW; 2. ref. to sensitivity / AW; 3. ref. to more qualitative / difficult to quantify; 4. ref. to, slow rate / inability to diffuse of some antibodies; 5. ref to problem of identifying individual antigens / AW; 2. the idea test will not detect low concentrations 4. Allow: – if ‘slow’ is in the context of getting results of tests [2] E antigen X + antigen Y 1 2 test organism 2 test organism 1

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2010 9700 51 © UCLES 2010 (c) (i) group 1 ref. to the idea of a control; group 2 and 3 ref. to idea of finding how many organisms, give immunity / needed; group 4 ref. to idea of finding the number of, inoculations / boosters, needed; Be careful they are not conclusions e.g. how many are needed (to make the vaccine work) e.g. to see if another booster is needed [3] P (ii) 2 of: ref. to (information that mutant) Plasmodium breeds / develops / AW in mosquitoes; ref. to breeding mosquitoes / culturing in salivary gland tissue / AW; ref. to extracting (Plasmodium) from salivary glands / culture of salivary glands; Allow: idea of a culture medium similar to salivary gland / saliva Ignore: from the liver of mice [2] M Total: [11]