Cambridge A Level Biology 9700 — 2009 May/June Paper 3 · Variant 2

This document consists of 12 printed pages and 4 blank pages. SPA (SHW 00338 7/08) V00357/5 © UCLES 2009 [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 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. You are advised to spend one hour on each question. * 4 0 5 9 8 7 4 8 3 6 * BIOLOGY 9700/32 Paper 32 Advanced Practical Skills May/June 2009 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions For Examiner’s Use 1 2 Total

9700/32/M/J/09 © UCLES 2009 For Examiner’s Use You are reminded that you have only one hour for each question in the practical examination. You should read carefully through the whole of each question and then plan your use of the time to make sure that you finish all the work that you would like to do. You must record all your results and will not be penalised if these results are not as expected. 1 Yeast cells contain enzymes, which catalyse the breakdown of glucose to produce carbon dioxide. You are required to investigate the effect of different concentrations of salt on the activity of yeast cells. You are provided with: • at least 50 cm3 10% salt solution, labelled S • at least 100 cm3 of an active yeast suspension in a glucose solution, labelled Y • at least 100 cm3 distilled water, labelled W • 10 cm3 syringe • plastic pipette • five beakers You are going to change the independent variable, the salt concentration. 10 cm3 of each salt concentration is mixed with 10 cm3 of yeast suspension so this will halve the concentration of the salt when mixed with the yeast. Table 1.1 shows how to make up two of the salt concentrations you should use. Table 1.1 volume of distilled water / cm3 volume of 10% salt solution / cm3 percentage concentration of salt percentage concentration of salt when mixed with yeast 10 0 0 0.0 5 5 5 2.5 2

3 9700/32/M/J/09 © UCLES 2009 [Turn over For Examiner’s Use (a) (i) Using the information in Table 1.1, decide which other concentrations to make and complete Table 1.2 including the concentrations from Table 1.1. Table 1.2 beaker volume of distilled water / cm3 volume of 10% salt solution / cm3 percentage concentration of salt percentage concentration of salt when mixed with yeast [3] 1. Use the syringe to make up the salt concentrations in the beakers. 2. Stir the yeast suspension in Y. 3. Clean the syringe. 4. Use the syringe to slowly pull up 10 cm3 of the yeast suspension Y from below the froth. 5. Add 10 cm3 yeast suspension to a beaker. 6. Stir well. 7. Repeat steps 2 to 6 with the other beakers. Leave for 5 minutes. While you are waiting, continue with steps 8 to 10. 8. Clean the syringe.

4 9700/32/M/J/09 © UCLES 2009 For Examiner’s Use 9. Use the plastic pipette to make a nozzle to fit the syringe by measuring and cutting off 3.5 cm from the end of the pipette. The syringe, with the nozzle attached, needs to hang into a tube as shown in Fig. 1.1. syringe plastic nozzle large test-tube Fig. 1.1 10. Remove the nozzle. 11. Use the syringe to pull up 9 cm3 of the mixture in the first beaker. 12. Remove the syringe from the mixture and pull the plunger up to the 10 cm3 mark. 13. Attach the plastic nozzle firmly to the syringe and, pointing it downwards over the first beaker, push the plunger gently so that the liquid fills the nozzle. 14. Hang the syringe in the tube as shown in Fig. 1.1. Drops of yeast suspension should form at the end of the nozzle and drip into the tube. 15. Wait for two minutes. 16. After two minutes count the number of drops over a suitable time. 17. Clean the syringe. 18. Repeat steps 10 to 17 with the contents of the other beakers.

5 9700/32/M/J/09 © UCLES 2009 [Turn over For Examiner’s Use (ii) Prepare the space below and record your results. [4] (iii) Identify two of the most significant errors in the experiment. 1. … … 2. … … [2] (iv) The nozzle was measured using a ruler. State the smallest division on the ruler …………… State the degree of uncertainty in using the ruler …………… [1] (v) Suggest how you would make sure your results are as accurate as possible, … … … … as reliable as possible. … … … … [3]

6 9700/32/M/J/09 © UCLES 2009 For Examiner’s Use (b) In a similar investigation, a student made up different masses of dried yeast into a suspension with 10% glucose solution and measured the percentage of light absorbed by the suspension (absorbance %). The results of the student’s investigation are shown in Table 1.3. Table 1.3 mass of dried yeast / g 100 cm–3 glucose solution mean percentage absorbance 1.00 9 1.50 17 2.00 39 2.25 53 3.00 94 (i) Plot a graph of the data in Table 1.3. [4]

7 9700/32/M/J/09 © UCLES 2009 [Turn over For Examiner’s Use A student investigated the growth of yeast. The dry mass of 1.50 g of yeast in 100 cm3 glucose solution has an absorbance of 17%, as shown in Table 1.3. The student measured the percentage absorbance after one day and after three days. The first result is shown in Table 1.4. Table 1.4 time/ days mean percentage absorbance mass of dried yeast / g 100 cm–3 glucose solution 0 17 1.50 1 60 3 25 (ii) Complete Table 1.4 using the graph. [1] (iii) Show clearly on the graph how you obtained the mass of dried yeast after one day and after three days. Put your answer on the graph that you plotted. [1] (iv) In carrying out this investigation the student made the hypothesis that: There will be a higher mass of dried yeast after two days. State whether you think that this hypothesis is supported by the student’s results. Explain your answer. … … … … [2] [Total: 21]

8 9700/32/M/J/09 © UCLES 2009 For Examiner’s Use 2 K1 is a slide of a stained transverse section of a plant organ. (a) (i) Draw a large, low power plan diagram of one end of the specimen on K1 as shown in Fig. 2.1. vascular bundle draw this section end Fig. 2.1 Annotate your drawing to describe the visible appearance of two tissues. [6]

9 9700/32/M/J/09 © UCLES 2009 [Turn over For Examiner’s Use (ii) Make a large, labelled, high-power drawing of two epidermal cells and the cells which form the layer inside touching these two cells. You should draw the epidermal cells from the region shown in Fig. 2.2. draw cells from this region Fig. 2.2 [5]

10 9700/32/M/J/09 © UCLES 2009 For Examiner’s Use (b) Fig. 2.3 shows a stage micrometer viewed through a microscope on a power of × 40 with an eyepiece graticule. Each division on the stage micrometer is 100
m (0.1 mm). 0 2 4 6 8 10 Fig. 2.3 Using the formula for the area of a circle r2 where  = 3.14 and r is the radius of the field of view, calculate the area of the field of view. Show your working. area of field of view … mm2

12 9700/32/M/J/09 © UCLES 2009 For Examiner’s Use Fig. 2.4 is a photomicrograph of the lower surface of a leaf, with the same field of view as in Fig. 2.3. magnification × 100 Fig. 2.4 Count and record the number of stomata in the field of view. Mark on Fig. 2.4 the stomata counted. Calculate the number of stomata per mm2. … mm–2 [5]

13 9700/32/M/J/09 © UCLES 2009 For Examiner’s Use (c) Fig. 2.5 is a photomicrograph of the lower surface of a different leaf. magnification × 100 Fig. 2.5 Prepare the space below so that it is suitable for you to show the difference between the surfaces of the leaves shown in Fig. 2.4 and Fig. 2.5. Record your observations in the space which you have prepared. [3] [Total: 19] [Paper total: 40]

16 9700/32/M/J/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.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2009 question paper for the guidance of teachers 9700 BIOLOGY 9700/32 Paper 32 (Advanced Practical Skills 2), maximum raw mark 40 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 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 – May/June 2009 9700 32 © UCLES 2009 Question Expected Answers Additional Guidance Mark 1 (a) (i) Decide which other salt concentrations to make and complete the table. 0 and 5% salt plus at least three evenly/serial spaced ignoring 0; e.g. 5/3.75/2.5/1.25 or serial 10/5/2.5/1.2 or 5/2.5/1.25/0.625 or 1/3/5/7 check any others. correct volumes used to dilute up to 10 cm3 AND correct % salt AND correct % of yeast and salt half % salt; Credit rounding up or down and from 0.5 either way. MMO decisions 3 (tubes listed) either most dilute/lowest % to most concentrated % or most concentrated to most dilute; Ignore 0. Ignore % in body of table. [1] [1] [1] (ii) Prepare space and record results. PDO recording 2 MMO collection 2 single table AND all cells drawn AND %/percent(age); (number/no. of) drops/AW; (heading to the left or above the data) suitable time with units e.g. per minute/min/min–1/ secs/seconds/s maximum time 5 minutes, minimum time 30 sec; any two different concentrations/tubes show different numbers of drops; heading heading heading heading heading Do not credit if % in body of table. Do not credit bubbles or if drops repeated in table. Ignore mean/time in table Credit anywhere even outside the table [1] [1] [1] [1]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (iii) Identify two of most significant errors ACE interpretation 1 different times before measuring/timing not the same; drops have air bubbles/different sizes/different masses/too fast; not airtight/air lock/froth/bubbles in nozzle; Do not credit not enough time. [max 2] (iv) State degree of uncertainty (of ruler used). ACE interpretation 1 +/– AND either half smallest division OR whole smallest division AND units/cm/mm; Ruler has error at each end of measurement of half smallest division = +/– half a division × 2 = +/– whole division with units mm. Credit half division as ruler may have started at zero. Do not credit % error unless candidate shows formula including the measured length of the pipette i.e. 3.5 cm /35 mm. e.g. 0.1/3.5 × 100 = +/– 2.8% or 1/35 × 100 = +/– 2.8% 0.05/3.5 × 100 = +/– 1.4 cm etc.% [1]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (v) Suggest how to make sure results are as accurate as possible and as reliable as possible ACE improvements 3 C (identification or control of any relevant variables) use buffer/same pH same type of yeast keep time same/set up separate expts/stagger time; Ignore use water bath/same temp. Accuracy: collect volume using measuring cylinder/video/time lapse photography/alternative method/ credit idea of making sure all drops are counted e.g. removal of all air locks in context /AW; Reliability 1: increase number/range of concentrations/2 named examples; Reliability 2: repeats more/several times/twice/obtain three readings (at each concentration)/collect class data (for same expt.); Reliability 3: calculate mean/average; Credit in either accuracy or reliability. Accuracy: (change/improvement to method of measuring to obtain results as close as possible to the true value) Reliable: (method to control variables so more repeatable) Do not credit repeat experiment unqualified. Do not credit three reliability marks. [1] [1] [1] [1] [1] [max 2]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (b) (i) Plot a graph of the data shown in Table 1.3. PDO layout 4 O x-axis mass of (dried) yeast (/)g 100 cm–3 glucose solution y-axis % or percentage, absorbance; S y axis 20 to 2 cm and x axis 0.5 to 2 cm; Credit origin 0.50/1.00 if labelled. P plotting correct points using crosses/dots in circles only; Do not credit if any extra points plotted in same way as other points e.g. at 60% or 25%. No 2 crosses larger than x or blobs bigger than o. Plots at 1.00, 1.50, 2.00 and 2.25 must be within the horizontal lines for the correct box plot 3.00 must be on horizontal line and correct vertical. L curve through at least 4 points/points joined with straight line; Quality – line no thicker than 1 mm thick Complete line should be smooth/not feathery. Do not credit S if awkward scale. Must use more than half the grid in either direction. Do not credit P plotting if awkward scale or if only blobs/dots/blobs in circles. Ignore extrapolation to zero. Do not credit any extrapolation beyond the last horizontal/vertical lines or extrapolation which does not reach zero. [1] [1] [1] [1] (ii) Complete the Table 1.4 (readings at 60% and 25% absorbance using graph). ACE interpretation 1 correct readings from candidate’s graph at 60 and 25% absorbance to two decimal places; 2.40 and 1.70 most likely. Must be to two decimal places as in table. [1] (iii) Show clearly on the graph how you obtained the mass. ACE interpretation 1 for both vertical and horizontal lines; Credit even if reading from wrong value. [1]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (d) State whether you think the hypothesis is supported by the student’s results. Explain your answer. ACE conclusion 2 not true/no; decreases between day 1 and day 3 or quote of data or not enough data/ described; true/yes; mass on day 1/quoted and day three/quoted are higher than day 0/quoted OR 0/quoted 5 absorbance between days 1 and 3 showing it would be higher or add mass for day 1 and day 3 and divide by 2 = 2.00; no and then yes or yes then say no or partly or might be true; not enough data/described; Credit ecf from their results Credit statement – even if the supporting argument is weak. [1+1] [1+1] [1+1] [Total: 21]

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 Question Expected Answers Additional Guidance Mark 2 (a) (i) Draw large low power plan section given. Annotation. PDO layout 1 MMO collection 3 MMO decision 2 clear, sharp, unbroken lines AND no shading AND cannot fit totally within the acetate grid; no cells AND epidermal layer drawn as two lines; 1 or 2 vascular bundles AND a closed tapering end; shows a region at the closed tapered end (for collenchyma); Any TWO from: (epidermal cells) clear/large/ thin cell walls/one cell thick; (collenchyma cells) thick cell walls/densely stained/small; (mesophyll cells) red cells/irregular/rectangular shapes/loosely-packed/ spaces; (xylem) large cells or vessels/lignified/red/brown/thick walls/ clear; (phloem) small cells; Credit tissue red etc. reject large tissue idea. Ignore lumen/hollow/empty/air/labels look for the line and apply description Credit any correct description. Do not credit functions. [1] [1] [1] [1] [max 2]

Page 8 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (ii) Make a large labelled drawing of 2 epidermal cells and the cells which form the layer inside touching these two cells. clear, sharp, AND unbroken lines For any cells drawn. no shading AND cannot fit totally within the acetate grid 6 cm × 6 cm; For the complete drawing. only 2 complete epidermal cells drawn AND at least 2 complete cells underneath touching; valid observation; Do Not credit if textbook or too much detail epidermal cells oil droplet Do not credit if nucleus present projection on outer wall granules inside 1 cell shape has vertical sides and a bowed upper and lower surfaces PDO layout 1 MMO collection 1 PDO recording 1 MMO decisions 2 Any two correct epidermal/mesophyll/other layer of cell(s) cell wall nucleus (on mesophyll cell) Ignore on epidermis cytoplasm air space (between cells) chloroplast (in mesophyll cell) vacuole oil droplet/highly stained part of cell/darkened area/AW (in epidermal cell) Ignore starch grain/cell membrane [1] [1] [1] [max 2]

Page 9 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (b) Calculate the area of view. Count and record no. of stomata in field of view. Calculate no. of stomata per mm2. PDO display 1 MMO collection 1 MMO decision 1 MMO collection 1 PDO display 1 calculation of field of view shown; 3.14 × 0.152 or 3.14 × (1.5 × 10–1)2 (3.14 × 1502)(/1000 000 or 106); Credit (3.14 × 3002/4) (/1000 000/106 or × 10–6) ref to 0.15 mm/150 µm; (uses stage micrometer to obtain) diameter 300 µm/0.3 mm or radius/0.15 mm/ 150 µm; marks stomata on fig. AND between 20 and 36; shows number of stomata divided by their calculated area/correct answer whole number only; [1] [1] [1] [1] [1]

Page 10 Mark Scheme: Teachers’ version Syllabus Paper GCE A/AS LEVEL – May/June 2009 9700 32 © UCLES 2009 (c) Show the differences between the cells in Fig. 2.2 and Fig. 2.4. PDO recording 1 organise as a table/ Venn diagram/ ruled connected boxes headed comparative statements opposite each other; First two statements. ACE interpretation 1 ACE conclusion 1 feature Fig. 2.4 Fig. 2.5 number of stomata/ cells more/calculated no. per mm2 fewer/calculated no. per mm2; size of stomata/cells smaller larger/longer; shape of stomata/cells oval/rounded/irregular/ puzzle-shaped/ rectangular/triangular/ regular; orientation of stomata/ cells random/scattered/ irregular lined up/parallel; /regular; (epidermal) cell walls thinner/smoother thicker/rougher/ folded; (folded/irregular) all round folded along sides/no folds at ends; Ignore stomata open and closed/sunken. Ignore drawings credit annotations if comparative [max 2] [Total: 19]