Cambridge A Level Biology 9700 — 2008 May/June Paper 3 · Variant 2

This document consists of 10 printed pages and 2 blank pages. SPA (FF/DT) T59335/4 © UCLES 2008 [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 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. * 3 2 5 4 0 8 3 9 4 4 * BIOLOGY 9700/32 Paper 3 Advanced Practical Skills May/June 2008 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Instructions to Supervisors. Onion Celery The length of the smallest division on the stage micrometer scale For Examiner’s Use 1 2 Total

2 9700/32/M/J/08 © UCLES 2008 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 of the work that you would like to do. 1 You are required to investigate the effect of different strengths of sucrose solutions on plant leaf tissue. You are provided with two lengths of plant leaf, labelled P1. You are also provided with two sucrose solutions. The first, labelled T1, is a 0.6 mol dm–3 solution of sucrose. The second labelled X1 is a sucrose solution of unknown strength. Using the solution T1 and the distilled water, make up 10 cm3 of a range of four or five solutions ranging from 0.0 to 0.6 mol dm–3 of sucrose into the four or five large test-tubes. Label the test-tubes and place them next to the test-tube labelled X1. Tick the material being used onion … celery … INSTRUCTIONS FOR ONION Using a scalpel or sharp blade, trim the length of the leaf to 20 mm as accurately as you can. Then cut the plant leaf into vertical strips, each 20 mm long, as shown in Fig. 1.1. cut along dotted line cuts to give at least five strips Fig. 1.1 Decide how many strips to add to each of the large test-tubes. INSTRUCTIONS FOR CELERY Using a scalpel or sharp knife, carefully cut off the outer layer (with ridges), in wide strips less than 5 mm thick as shown in Fig. 1.2. ridge ridges on top ridge 20 mm cut down cut cut Fig. 1.2 Place the wide strip with the ridges on top on the cutting surface and cut into thin strips between the ridges as shown in Fig. 1.2. Then carefully cut to 20 mm lengths. Decide how many thin strips to add to each of the large test-tubes.

3 9700/32/M/J/08 © UCLES 2008 [Turn over For Examiner’s Use Leave for at least 20 minutes once you have added the strips to the test-tubes. While you are waiting you may start Question 1(e). Pour the solution and the strip(s) from one test-tube into a Petri dish. Carefully remove a strip from the Petri dish and blot dry with a paper towel, re-measure without altering the strip and record your observations. Repeat this procedure for each of the strips from the other test-tubes. (a) Prepare and use the space below to record how you made up the solutions, the concentration, and the measurements you made, including X1 and any observed changes to the strips. [5] (b) Estimate the concentration of sucrose solution X1 from your observations. … [1]

4 9700/32/M/J/08 © UCLES 2008 For Examiner’s Use (c) Describe and explain the results from all the solutions that you made. … … … … … [3] (d) (i) Identify two significant sources of error in this experiment. 1 … … 2 … … [2] (ii) Suggest how you could improve this experiment. … … … … … [3] (e) A student investigated the effect of sucrose concentration on the diameter of red blood cells. The original diameter of the red blood cells was 7.0 µm. The results are shown in Table 1.1. Table 1.1 concentration of sucrose solution / mol dm–3 0.05 0.10 0.20 0.40 0.80 diameter of cell 1 / µm 8.4 7.2 6.6 5.7 2.3 diameter of cell 2 / µm 7.8 7.3 6.8 5.7 2.5 diameter of cell 3 / µm 8.1 7.4 7.0 5.5 2.4 mean diameter / µm 8.1 7.3 6.8 2.4 mean change in diameter / µm +1.1 +0.3 − 0.2 − 4.6

5 9700/32/M/J/08 © UCLES 2008 [Turn over For Examiner’s Use (i) Complete Table 1.1 by calculating the missing mean diameter and mean change in diameter for solution 0.40 mol dm–3. Write your answer in Table 1.1. [1] (ii) When the student first performed this investigation, the diameter of cell 2 in 0.20 mol dm–3 solution was 3.1 µm. Explain why the student discarded this result and repeated the experiment with freshly made solutions. … … [1] (iii) Plot a graph to show the effect of sucrose concentration on the mean diameter of red blood cells. [3]

6 9700/32/M/J/08 © UCLES 2008 For Examiner’s Use (f) The student’s hypothesis was: The greater the concentration of sucrose solution, the greater the diameter of red blood cells. Draw an appropriate conclusion to the student’s experiment. You should include in your conclusion whether the experimental data support the hypothesis and you should produce a revised hypothesis if necessary. … … … … … [2] [Total: 21]

7 9700/32/M/J/08 © UCLES 2008 [Turn over For Examiner’s Use 2 K1 is a slide of a stained transverse section through a plant stem. You are also provided with an eyepiece graticule that has been fitted to the eyepiece of your microscope and a stage scale (stage micrometer) printed on acetate sheet. (a) (i) Draw a large low-power plan diagram of a quarter of the specimen K1 as shown in Fig. 2.1. Labels are not required. drawing of this part required Fig. 2.1 [4]

8 9700/32/M/J/08 © UCLES 2008 For Examiner’s Use (ii) Carefully examine one of the larger vascular bundles using the low-power of your microscope. Count the number of eyepiece graticule divisions across this vascular bundle from the outer edge towards the centre (radial width). Indicate by drawing a line on your low power plan, precisely where you made your measurement. number of eyepiece graticule divisions … Remove the slide K1 and replace it with the stage micrometer scale. The length of the smallest division on the stage micrometer scale is … mm. Using the same magnification, adjust the focus until you can see the eyepiece graticule on top of the stage micrometer scale. Count the number of eyepiece graticule divisions that match an exact number of stage micrometer scale divisions. number of eyepiece graticule divisions … number of stage micrometer scale divisions … Use this information to calculate the actual radial width of the vascular bundle. Show your working. actual radial width of the vascular bundle … µm [4] (iii) Suggest how an error in measuring the vascular bundle could occur. … … [1]

9 9700/32/M/J/08 © UCLES 2008 [Turn over For Examiner’s Use (iv) In the space below, make a large high-power drawing of phloem tissue only. Draw five cells that are in contact with each other. Include at least one companion cell in your drawing. [4]

10 9700/32/M/J/08 © UCLES 2008 For Examiner’s Use (b) Fig. 2.2 is a photomicrograph showing a transverse section of a different stem. region Y X 10 Fig. 2.2 (i) Suggest the purpose of region Y as shown on Fig. 2.2. … … [1] (ii) Prepare the space below so that it is suitable for you to compare and contrast the stem on slide K1 with the stem in Fig. 2.2. Record your observations in the space that you have prepared. [5] [Total: 19]

12 9700/32/M/J/08 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 2008 question paper 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. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. 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 2008 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 Skill Total marks Breakdown of marks Question 1 Question 2 successful collection of data and observations 8 marks 2 6 Manipulation, measurement and observation 16 marks nature of measurements or observations 8 marks 5 3 recording data and observations 4 marks 2 2 display of calculation and reasoning 2 marks 1 1 Presentation of data and observations 12 marks data layout 6 marks 3 3 interpretation of data or observations and identifying sources of error 6 marks 3 3 drawing conclusions 3 marks 2 1 Analysis, conclusions and evaluation 12 marks suggesting improvements 3 marks 3 0 MMO = Manipulation, measurement and observation Collection = successful collection of data and observations Decisions = decisions relating to measurements or observations PDO = Presentation of data and observations Recording = recording data and observations Display = display of calculation and reasoning Layout = data layout ACE = Analysis, conclusions and evaluation Interpretation = interpretation of data or observations and identifying sources of error Conclusions = drawing conclusions Improvements = suggesting improvements ecf = error carried forward AW = alternative wording ora = or reverse argument

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 Q Expected Answers Additional Guidance Marks 1 (a) How solutions made, concentration, measurements and observations. 2 PDO display, 2 MMO collection, 1 MMO decision [5] 1 single table, all cells drawn; 2 column headings: concentration/mol dm–3 to left/across top, any one of length/mm/change in length/mm/volume cm3 or ml; 3 in table changes shown, 0.6, gets smaller/–ve, water, gets no change/longer/+ve; 4 volume kept the same; 5 at least two of 0.4/0.3/0.2/0.15; Mark first table, ignore other tables/further writing. No outer boundary needed. M or molar or mole(s)/l or per litre. Allow strength. No units in table. Must have units. Read from final length results in table. Allow if not shown in table. Mark for volumes anywhere. allow 0.48/0.42/0.36/0.24/0.18/ 0.12/0.06 Check Supervisor’s report for their results but mark according to mark scheme. Reject point 3 if heading units different from those recorded. (b) Estimate the concentration of sucrose in X1. ACE interpretation [1] correct concentration from results, mol/dm3 or mol dm–3; Match any one correct. Or allow between correct values but no made up estimate and must have units M or molar or mole(s)/l or per litre

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 (c) Describe and explain the results from all the solutions that you made. 3 MMO decisions [3] concentration from results table, correct increase/decrease/no change in length; correct ref to direction of water movement, correct ref to water potential gradient; by osmosis; Ignore X1. Allow for their results even if wrong. Allow general statement. If no change then water moving in both directions/no net water movement. Higher or high to low/er WP ora. If no changes in length recorded, allow 20mm/2cm – final length. (d) (i) Describe and explain the results from all the solutions that you made. 2 ACE interpretation [2] changes are small/accuracy of measuring/ruler +/–1mm/parallax error; widths are not standard; syringe qualified with ref. to uncertainty/large size vs coarse measurement; evaporation of solution; strips float/not immersed; no/not enough repeats/replicates; times different/not possible to add/remove at same time; Mark any correct. Reject bubbles in syringe. Reject if just syringe not accurate. Must have +/– (ii) Suggest how you could improve this experiment. ACE improvements [3 max] more concentrations/examples (at least 2) any between those given; smaller syringe/syringe with lower uncertainty/finer divisions; method/how to remove bubbles in syringe; longer strips; cover solution; repeat/use more strips; use burette/graduated pipette; use vernier callipers; do one experiment at a time/timed sequence/AW; (e) (i) Complete the Table 1.1 by calculating the missing value. PDO display [1] 5.6, –1.4; Only these answers.

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 (ii) When the student performed this investigation, the diameter of cell 2 in 0.20 mol dm–3 solution was 3.1 µm. Explain why the student discarded this result and repeated the experiment with freshly made solutions. MMO decision [1] reading should have been more/too low/reading anomalous/not reliable/does not fit trend; Allow idea of e.g. reading is odd/completely different. Ignore just some error. O x-axis conc.(sucrose)/mol dm–3 or mol/dm3; M or molar or mole(s)/l or per litre S/P scale x-axis 0.2 to 2cm and y-axis uses half or more plotting crosses or dot in circle ONLY, correct for correct graph i.e. mean diameter of red blood cells only; Allow ecf from their figures/ crosses in circles Ignore if 0 not at origin but if scale starts at 0.2 then must have 0.2. Reject if mean change. Reject 1 mm or more blobs in circles. Ignore shape of circles. L either ruled/straight lines joining each point/ ruled line of best fit with 2 one side and one the other/one on the line and two each side of the line; If join the dots, then allow only 1mm/half square extension beyond first and last point. If line of best fit then allow 2mm/one square at 0.8/high concentration and to the axis for 0.05/low concentration end Reject line if more than 1mm thick (f) The greater the concentration of sucrose solution, the greater the diameter of red blood cells. ACE conclusions [2] hypothesis wrong/incorrect; as the concentration increases, the diameter of cells decreases/inversely proportional; ORA Needs clear statement. Idea of correct relationship may quote figures to get same idea. Reject idea that not totally wrong.

Page 6 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 2 (a) (i) Draw a LARGE, LOW-POWER plan diagram of part of specimen K TS Ranunculus. 1 MMO collection, 3 PDO layout [4] (quarter that is) 4 to 7 vascular bundles drawn, sharp, clear unbroken lines; no cells, larger than 6 cms in any one direction; distance of outer epidermis to top of nearest vascular bundle less than top of vascular bundle to pith; largest vascular bundle at least twice size of smallest vascular bundle; Ring 3 errors on simple diagram then reject. Use acetate square, accept if any line outside. Ignore labels. If more than a quarter drawn, then max1 point 2 only. Reject if no pith drawn or a dotted line.

Page 7 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 (ii) Use this information to calculate the actual width of the vascular bundle. 2 MMO collection, 1 PDO recording, 1 PDO display [4] How to mark the calculation. Step 1: W
(1) X Y Z Step 2: Calculate the answer USING their figures (Z/Y × X × W) ×1000 Step 3: Answer correct AND rounded correctly to 1 decimal place only. Round 0.5 up or down. If close, check where they may have rounded differently.


Answer correct BUT not rounded or rounded incorrectly.

Answer wrong. Go back to working MUST show Z/Y × X × W – all figures must be there and doing the correct thing in whatever order OR have calculated it correctly (ignore decimal figures).
AND Look for ×1000 or × 103. Must be shown not implied.
Either between 2 and 3.5 any 1 decimal place OR between 20 and 35.5 only allow .5 no other decimals.

Page 8 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 (iii) Suggest how an error in measuring the vascular bundle could occur. ACE interpretation [1] thickness of lines/difficult to line up scales/depth of focus/not knowing where edge of vascular bundle is; Allow focussing problem/blurring/aligning. Ignore can’t count/do a mean/average/other excuses. Reject scale not calibrated correctly. Ignore parallax. (iv) Make a LARGE, HIGH-POWER drawing of 5 cells to include a companion cell. 1 MMO collection, 3 MMO decisions [4] 5 complete cells, all touching (one group of five cells); sharp, clear unbroken lines, larger than 6 cm in any one direction; (companion cell) smallest cell drawn less than a quarter of the largest cell (phloem sieve tube), no more than one nucleus in a smaller cell, no sieve plates; all cells have single line walls, no shaded walls, no intercellular spaces; Reject if more than 6 cells/no marks for textbook diagrams. 3 rings for errors reject touching cell wall lines/incomplete cell walls. Use acetate square. Reject if drawing not like slide e.g. too much detail drawn sieve plate and pores between cells or nuclei in cells.

Page 9 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9700 32 2 (b) (i) Suggest the purpose of the region Y (collenchyma cells) in corner of stem. ACE conclusion [1] support stem/keep shape of stem/makes corner; Allow strengthening (ii) Compare and contrast TS Ranunculus with Fig 2.2. 2 MMO collection, 1 PDO recording, 2 ACE interpretation [3 max] organise as a table/venn diagram/ruled connected boxes, correctly labelled; (1) comparative statements opposite each other/in one sentence; (1) THREE from: K1 (Ranunculus) Fig 2.4 (pith) space in middle/no pith, no space/has pith; (shape) circular/no corners, no protrusions/AW/Y, square/has (4) corners protrusions/AW/has Y; (vascular bundles) lots/many, all round/evenly spaced, rounded shape/oval, big and small, arranged around sides, few/not as many; mainly in corners/square; shape described/curved; big and small; arranged round sides; AVP; no trichomes/AW, trichomes; First table ignore additional e.g. similarities separate table minimum. Allow similarities vs differences as column headings. Allow for one statement as comparison. Reject two separate lists. Reject spherical.