Cambridge A Level Biology 9700 — 2009 Oct/Nov Paper 5 · Variant 1

This document consists of 7 printed pages and 5 blank pages. DC (DR/DR) 13147/4 © UCLES 2009 [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 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. * 7 3 3 8 2 0 6 8 8 3 * BIOLOGY 9700/51 Paper 5 Planning, Analysis and Evaluation October/November 2009 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. For Examiner’s Use 1 2 3 Total

3 9700/51/O/N/09 [Turn over For Examiner’s Use © UCLES 2009 1 An investigation into the effect of temperature on the rate of the light-dependent stage of photosynthesis was carried out using isolated chloroplasts. Samples of chloroplasts suspended in buffer were mixed with a coloured electron acceptor and exposed to light. The colour changes from blue to colourless as electrons are taken up by the electron acceptor. (a) (i) Sketch a graph to predict the results of the investigation. [2] (ii) Identify two key variables that must be controlled in this investigation. For each explain how it might be controlled. 1… … … 2. … … …[4] (iii) Outline a procedure to find the rate of reaction for this investigation. … … …[2] (b) In a further investigation, small quantities of ADP and inorganic phosphate were added to the isolated chloroplasts before testing. Suggest an hypothesis being tested by this further investigation. … …[1] [Total: 9]

4 9700/51/O/N/09 For Examiner’s Use © UCLES 2009 2 A solution of substance Y, thought to be a growth hormone, was made by dissolving a known mass of Y in 10 cm3 of distilled water. This solution was added to samples from a culture of animal cells containing 3000 cells per mm3. • 25 mm3 of solution Y was added to a cell sample. • 25 mm3 of distilled water was added to another cell sample. After four days the number of cells per mm3 of each culture was estimated using a microscope slide with a counting grid. (a) Identify and explain the purpose of the control experiment used in this investigation. … … …[2] (b) Fig. 2.1 shows a top view of a microscope slide with a counting grid. Fig. 2.2 shows a vertical section through the microscope slide and grid. Fig. 2.3 shows the detail of part of the grid viewed through a microscope. 0.2mm 0.2mm cell 0.05mm position of counting grid on slide cover glass cover glass on sample of 0.1mm depth position of counting grid on slide Fig. 2.1 Fig. 2.2 Fig. 2.3 www.OnlineExamHelp.com

5 9700/51/O/N/09 [Turn over For Examiner’s Use © UCLES 2009 Suggest how this apparatus could be used to estimate the number of cells per mm3 of culture. … … … … … … … …[4] (c) Table 2.1 shows estimated number of cells in the experimental and control cultures after three days growth. Table 2.1 thousands of cells per mm3 of culture sample number 1 2 3 4 5 6 7 8 9 10 mean experimental culture 7.5 8.1 7.6 6.2 7.5 7.8 8.9 6.5 7.9 7.3 7.5 control culture 5.6 7.5 8.2 6.7 3.5 6.5 5.9 3.7 5.8 8.4 (i) Complete Table 2.1 by calculating the mean number of cells per mm3 in the control culture. Write your answer in Table 2.1. [1] (ii) A student correctly calculated the percentage increase in the number of cells per mm3 in the experimental culture as 151% using the formula: (final number – original number) × 100 original number Calculate the percentage increase in the control culture. Show your working. … [1]

6 9700/51/O/N/09 For Examiner’s Use © UCLES 2009 (d) The student’s hypothesis for the investigation was: Substance Y promotes growth in animal cell cultures. (i) Identify evidence from the results that supports this hypothesis. … … … … … (ii) Identify evidence from the results that does not support this hypothesis. … … … … …[4] [Total: 12]

7 9700/51/O/N/09 [Turn over BLANK PAGE QUESTION 3 STARTS ON PAGE 8

8 9700/51/O/N/09 For Examiner’s Use © UCLES 2009 3 (a) Polychlorinated biphenyls (PCBs) are persistent organic pollutants. Their use has been banned in many countries. The effects of these pollutants on male fertility has been investigated by many scientists. (i) One group of studies on fish indicates that some of these pollutants decrease the size of the testes in relation to body mass. Suggest a procedure by which the relative size of the testes of fish might be estimated. … … … … …[3] (ii) Name a statistical test that is suitable for determining if the decrease in the relative size of the testes is significant. Explain your choice. test … explanation …[2] (iii) Suggest one way in which the decrease in relative size of the testes may lower fertility of fish. … … …[1] www.OnlineExamHelp.com

9 9700/51/O/N/09 For Examiner’s Use © UCLES 2009 (b) Another group of studies tested the effect of one type of PCB, CB-153, on the DNA of human sperm. In this study, the concentration of CB-153 present in the lipid in the blood plasma of fishermen was measured. The DNA of a sperm sample was labelled using a fluorescent marker. Undamaged DNA fluoresces green and damaged DNA fluoresces red. The proportion of damaged DNA can be calculated as a DNA fragmentation index. The data was grouped into six equal sized groups and plotted in relation to the concentration of CB-153 in the lipid in the blood plasma. Fig. 3.1 shows the results of this study. 2.0 2.2 2.4 2.6 2.8 3.0 3.2 0 60 120 180 concentration of CB-I53 in lipid of blood plasma / ng per g lipid 240 300 360 DNA fragmentation index / arbitrary units Fig. 3.1 State the conclusions that can be drawn from this investigation about the effect of CB-153 on the DNA of human sperm. … … … … … …[3] [Total: 9]

12 9700/51/O/N/09 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. www.OnlineExamHelp.com

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the October/November 2009 question paper for the guidance of teachers 9700 BIOLOGY 9700/51 Paper 51 (Practical 2), 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 October/November 2009 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 A/AS LEVEL – October/November 2009 9700 51 © UCLES 2009 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 A/AS LEVEL – October/November 2009 9700 51 © UCLES 2009 Question Expected answer Extra guidance Mark AO 1 (a) (i) 2 of; axes correctly oriented and labelled; appropriate values and curve shown; 1/time or Rate of light dependent reaction temperature ºC Allow as minimum: rate on y axis and temp on x axis. Allow time-1 and oC. Do not allow rate of photosynthesis. [2] P (ii) For each factor, allow both marks anywhere in the answer. If two factors given in one answer, mark the first unless there is nothing written in no.2 For 1 and 2 – ignore amount/quantity for the variable, but not for the method of control. 2 × 2 of: 1. light intensity; use light of (same wattage) at same distance; 2. light wave length; use a known filter / coloured filter / coloured light bulb; 3. (quantity o)f chloroplasts; chloroplasts - using same mass / volume of chloroplast; suspension; 4. (quantity) of indicator / (electron) acceptor; indicator – same concentration/volume of indicator / (electron) acceptor; Ignore carbon dioxide concentration and pH. Allow a light in a dark room. Do not allow from the same plant. [2] [2] P M (iii) Take care that the question is not being repeated for ‘expose to light’. idea of: keeping covered / not adding acceptor (until ready to measure), (using stop watch) find time for colour to disappear/ change from blue to colourless; divide 1 / time to find rate; Allow any idea that the light is not switched on until measuring is carried out. Allow a formula. [1] [1] M D

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9700 51 © UCLES 2009 Question Expected answer Extra guidance Mark AO (b) idea of: (ADP and inorganic phosphate) will increase the rate (of the light dependent reaction); Ignore photosynthesis. [1] P Total: [9] P5 M3 D1 2 (a) (distilled) water; idea of: to show that the hormone / solution Y causes extra population growth / to show how much population growth occurs without hormone; Allow if the answer implies that any effect on population / cells is due to solution Y / hormone. [2] M (ii) 2 of: 1. ref. to adding sample to slide; 2. ref. to idea the sample is uniform; 3. ref. counting cells; 4. ref. to any detail of counting e.g. exclusions / number of squares; 2 of: 5. ref. to grid volume 0.2 mm × 0.2 mm × 0.1 mm = 0.004 mm3; 6. ref. to factor × 250 to estimate number of cells per mm3 / dividing by the grid volume (0.004 mm3); 7. ref. to counting min.3 areas / slides and taking mean; 3. Allow reference to number of cells. 4. Allow any recognised systematic method of measuring. 5. Allow any other sizes identified from diagram e.g. 0.1 × 0.1 × 0.1. 6. Allow marks from a formula. [2] [2] M D (c) (i) mean = 6.2; [1] D (ii) 107(%); 100 3 3.0) (6.2 = × − Do not allow fraction / decimal answers. Allow 106 if calculation shows 6.18 being used to find the percentage. Allow ecf for wrong mean in (c) (i). [1] D www.OnlineExamHelp.com

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9700 51 © UCLES 2009 Question Expected answer Extra guidance Mark AO (d) Must have at least one answer in each section and any 2 others support: 1. mean value of experimental cell culture is higher (than control); 2. percentage increase in greater in experimental culture; 3. bottom of range higher / top of range higher, in experimental cell culture (than control) / AW; does not support 4. range overlaps / ref. to specific examples of control and experimental samples which are the same ; e.g. control 6 and experimental 8 which are both 6.5 / some control samples have same value as experimental mean allow any refs. to limitations of procedure: 5. ref. to insufficient replication (for such variable data); 6. no statistical test of difference carried out / do not know if the difference is significant / no chi squared test / no t-test / no standard error calculated; 7. only one concentration tested / ref. limited range / AW; Do not allow isolated examples of comparisons between specific samples any where in the answer. 3. Idea that the figures at the lower end of the range are all higher in the experimental culture / ora OR the figures at the top end of the range are all higher for the experimental culture / ora. [4] E Total: [12] M4 D4 E4 3 (a) (i) 3 of: ref. to weighing / finding mass of the fish; ref. to suitable method of measuring testis e.g. mass / volume / length; ref to suitable units for chosen method e.g. g / kg / cm3 / cm; ref. to a sample of 3 or more and taking a mean; ref. to proportion calculated by, mass / volume / length testis divided by mass of body; Allow measurement of volume or length. Allow several / many / a number. Allow as a formula. Allow ecf from a fish mass without testis. Do not allow ref. ‘find the ratio’ unqualified. [3] M

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – October/November 2009 9700 51 © UCLES 2009 Question Expected answer Extra guidance Mark AO (ii) t-test; data is a continuous / shows a normal distribution / comparing differences in means; Allow ref. to lack of overlap of error bars. [2] D (iii) 1 of: fewer seminiferous tubules / fewer spermatogonia / less sperm produced; fewer endocrine / Leydig cells / less hormones (so fail to mature); [1] C (b) 1.ref. to values between 60–120 (ng per g lipid )show greatest increase in damage / fragmentation; 2. ref. to values above 120–180 (ng per g lipid) show that increase in (CB-153) concentration has little effect ; 3. ref. to no overlap in error bars between values at 60 and 120 (ng per g lipid) indicates the difference (in damage) is likely to be significant; 4. ref. to above 120–180 (ng per g lipid) error bars have a lot of overlap so (increase in damage) not likely to be significant; 1. Allow higher concentration (of CB-153) causes more( DNA) damage. 2. Allow ref. to non-linear relationship / seems to be threshold / shows a plateau. [3] C Total: [9] 3 M 3 D 3 C