Cambridge A Level Biology 9700 — 2008 May/June Paper 3 · Variant 1

This document consists of 10 printed pages and 2 blank pages. SPA (FF/DT) T58783/4 © 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. You are advised to spend one hour on each question. BIOLOGY 9700/31 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 The length of the smallest division on the stage micrometer scale For Examiner’s Use 1 2 Total * 1 6 7 0 8 2 7 9 4 1 *

2 © UCLES 2008 For Examiner’s Use 9700/31/M/J/08 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 carry out tests, using only the reagents provided, to identify each of the solutions S1, S2 and S3. One of the solutions is glucose, another a protein and the third a carbohydrate other than glucose. You are required to identify each of the solutions, S1, S2 and S3. You must use only the reagents provided. (a) (i) Prepare and use the space below to record the test used, observations and conclusions. [5]

3 © UCLES 2008 [Turn over For Examiner’s Use 9700/31/M/J/08 (ii) Describe and explain how you identified the carbohydrate that was not glucose. … … … … … … … [3] (iii) Use your results and the information in Table 1.1 to estimate the concentration of the glucose solution. Table 1.1 colour glucose concentration / mol dm–3 blue 0.00 green 0.01 yellow 0.05 red 0.10 concentration of glucose solution … [1] (iv) Identify two sources of error in estimating the concentration of the solution. 1 … … 2 … … [2]

4 © UCLES 2008 For Examiner’s Use 9700/31/M/J/08 (v) If you were to repeat this experiment to make a more accurate estimation of the glucose concentration, state how you would carry out your investigation. … … … … … … … … [3] (b) A student carried out an investigation on starch suspensions with various concentrations testing for starch with iodine in potassium iodide solution. To find the concentration of starch, the student used a colorimeter to determine the mean transmission of light through the solutions. Five replicates were run, starting with fresh materials each run. The data in Table 1.2 were obtained. Table 1.2 percentage concentration of starch suspension transmission of light / arbitrary units first run second run third run fourth run fifth run mean 0.0 92 91 92 94 89 92 0.5 61 60 59 60 58 60 1.0 41 41 42 43 41 42 1.5 31 30 30 29 31 2.0 25 23 25 23 24 24 2.5 22 23 21 23 21 22 (i) Complete Table 1.2 by calculating the missing value. [1] (ii) When the student performed this investigation, the transmission for a 2.5% suspension of starch in the first run was 95 arbitrary units. Explain why the student discarded this result and repeated the experiment with a freshly made solution. … … [1]

5 © UCLES 2008 [Turn over For Examiner’s Use 9700/31/M/J/08 (iii) Plot a graph of percentage concentration of starch suspension against the transmission of light using the student’s results. [3] (c) The student’s hypothesis was: Transmission of light is proportional to the concentration of starch suspension. Draw an appropriate conclusion to the student’s experiment. You should include in your conclusion whether the experimental data support the hypothesis and produce a revised hypothesis, if necessary. … … … … [2] [Total : 21]

6 © UCLES 2008 For Examiner’s Use 9700/31/M/J/08 2 J1 is a slide of a stained transverse section through the leaf of a xerophyte. You are also provided with an eyepiece graticule that has been fitted to the eyepiece of your microscope and a stage micrometer scale. (a) (i) Draw a large low-power plan diagram of a part of J1 as shown in Fig. 2.1. Labels are not required. drawing of this part required Fig. 2.1 [4]

7 © UCLES 2008 [Turn over For Examiner’s Use 9700/31/M/J/08 (ii) Fig. 2.2 is a photomicrograph of part of J1. tip of trichome base of trichome Fig. 2.2 Carefully examine a similar area of J1 using the high-power of your microscope. Put a ring round the number written on the objective lens. ×40 4 mm ¹
₆" other …… Identify a trichome (hair). Count the number of eyepiece graticule divisions across the width of the base of the trichome. number of eyepiece graticule divisions … Remove the slide J1 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 scale. Count the number of eyepiece graticule divisions that match an exact number of stage scale divisions. number of eyepiece graticule divisions … number of stage micrometer scale divisions … Use this information to calculate the actual width of the trichome on your slide J1. Show your working. actual width of trichome …µm [4]

8 © UCLES 2008 For Examiner’s Use 9700/31/M/J/08 (iii) Suggest how an error in measuring the trichome could occur. … … … [1] (iv) Suggest the purpose of the trichomes on the leaf of the xerophyte. … … … [1]

9 © UCLES 2008 [Turn over For Examiner’s Use 9700/31/M/J/08 (b) In the space below, make a large high-power drawing of three cells from the inner layer (at X) and three cells from the outer layer (at Y) of J1, as shown in Fig. 2.3. X Y Fig. 2.3 three cells from the inner layer (at X) three cells from the outer layer (at Y) [4]

10 © UCLES 2008 For Examiner’s Use 9700/31/M/J/08 (c) Fig. 2.4 is a photomicrograph of a transverse section of a leaf of another xerophyte. × 50 Fig. 2.4 Prepare the space below so that it is suitable for you to compare and contrast the section on slide J1, with the section shown in Fig. 2.4. Record your observations in the space that you have prepared. [5] [Total : 19] [Paper total : 40]

12 9701/32/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 Level MARK SCHEME for the May/June 2008 question paper 9700 BIOLOGY 9700/31 Paper 31 (Advanced Practical Skills 1), 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 LEVEL – May/June 2008 9700 31 © UCLES 2008 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

Page 3 Mark Scheme Syllabus Paper GCE A LEVEL – May/June 2008 9700 31 © UCLES 2008 Question Sections Learning outcomes Indicative material mark 1 (a) (i) MMO collection MMO decisions PDO recording Use their apparatus to collect an appropriate quantity of ..observations including subtle differences in colour. Sufficient distinct observations are made to identify the dissolved substances in a solution. Present …observations in a single table of results. Include in table of results columns for raw data and for deductions. Use column headings that …conform to accepted scientific conventions. all starch/iodine tests, negative/no colour change/orange/red; S2, violet/purple/mauve; S1, glucose, S2, protein, S3, carbohydrate/sucrose/non- reducing sugar; (all correct) single table drawn with all cells ruled; (1st/top) solution, colour changes/tests shown, conclusions/identification shown; 2 1 2 (ii) MMO decisions Qualitative observations consistent with materials supplied. Identify the dissolved substances in a solution. idea of blue/negative test with Benedicts; therefore not glucose; boil with acid/HCl, neutralise with sodium bicarbonate, repeat benedict’s test; 3 (iii) ACE interpretation Describe the patterns and trends shown by tables. correct estimate with colour change from their results, with units; 1 (iv) ACE interpretation Identify the most significant sources of error in an experiment. two from difficult to judge colour/may be between colours; volumes used different from those used for table; volume of Benedicts may have been different; heating time/temperature may have been different 2 max

Page 4 Mark Scheme Syllabus Paper GCE A LEVEL – May/June 2008 9700 31 © UCLES 2008 (v) ACE improvements Suggest modifications to an experimental arrangement that will improve the accuracy of the experiment or the accuracy of the observations that can be made, including the use of new methods or strategies to investigate the question. S1 use same volume/example of volume as for known glucose; add same/excess volume of Benedicts to S1 and known glucose; heat/boil for same length of time; repeat all measurements; use more known concentrations of glucose; e.g. of accurate use of equipment/buretter/graduated pipette; 3 max 1 (b) (i) PDO display Use correct number of significant figures for calculated quantities. 30; 1 (ii) MMO decisions Replicate readings or observations as necessary. anomalous/does not fit trend/pattern/described; 1 (iii) PDO layout Select which variables to plot and plot appropriately on clearly labelled x- and y- axes. Choose scales for the graph axes that allow the graph to be read easily, such as 1, 2 or 5 units to a 20mm square. Make the best use of the space available, using over half of the length and width of the grid. Plot all points to an appropriate accuracy. Follow IOB recommendations for putting lines on graphs. O percentage concentration of starch on x-axis, and mean transmission of light/arbitrary units on y-axis ; S scale, more than half grid(x and y) used for plotted area; P all points correctly plotted with crosses/dots (in circles), points joined with ruled lines/curve through all points; 3 (c) ACE conclusion Draw conclusion from an experiment…considering whether the experimental data supports a given hypothesis ..making further predicitions. idea that data does not (totally)support the hypothesis; as concentration of starch suspension increases the transmission of light changes slower/less after 1.5/2.0%; 1 1 Total 21

Page 5 Mark Scheme Syllabus Paper GCE A LEVEL – May/June 2008 9700 31 © UCLES 2008 2 (a) (i) MMO collection PDO layout Follow instruction given in the form of written instructions or diagrams. Use their apparatus to collect an appropriate quantity of data. Make drawings large, unshaded. Use fine, clear unbroken lines showing clear outlines of structures. half drawn, no cells drawn, no shading; (half) larger than 9 cm width and fine clear, unbroken lines; vascular bundles correctly placed; proportions correct; 4 (ii) MMO collection PDO recording PDO display Follow instruction given in the form of written instructions or diagrams. Make measurements using …graticules. Record raw readings of quantities to same degree of precision. Show working in calculations, key steps in working. number of epg divisions across trichome correct; correct answer and units for calculation; whole numbers of epg divisions; (epg divisions/no. of stage divisions) x epg divisions for trichome; 2 1 1 (iii) ACE interpretation Identify the most significant sources of error in an experiment. parallax/not knowing where base is; 1 (iv) ACE conclusion Draw conclusions from interpretations of observations. traps water/reduces evaporation; 1 (b) MMO collection MMO decisions Follow instruction given in the form of written instructions. Qualitative observations consistent with materials supplied. Show all structures that can be seen in a defined part of the specimen. 8–12 cells drawn; shape of cells as on slide; cell walls drawn; 2 correct labels;; 1 3 max

Page 6 Mark Scheme Syllabus Paper GCE A LEVEL – May/June 2008 9700 31 © UCLES 2008 (c) MMO collection ACE interpretation PDO recording Use their apparatus to collect an appropriate quantity of data or observations, including subtle differences in colour or other properties of materials. Describe and summarise key points of a set of observations. Make and record sufficient accurate measurements and observations. hairs/no hairs; rolled leaf/not rolled; circular/semicircular; vascular bundles separate/vascular bundles in middle; more vascular bundles/fewer vascular bundles; comparative statements opposite each other; organised as a table/venn diagram/ruled connected boxes, correctly headed; 2 + 1 (3) max 1 max 1 Total 19 Paper Total 40