Cambridge A Level Biology 9700 — 2012 May/June Paper 3 · Variant 3

This document consists of 12 printed pages. DC (LEO/CGW) 37143/7 © UCLES 2012 [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 ink. You may use a pencil for any diagrams, graphs or rough working. Do not use red ink, staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. You may lose marks if you do not show your working or if you do not use appropriate units. 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. * 6 5 8 7 8 7 5 1 1 7 * BIOLOGY 9700/33 Advanced Practical Skills 1 May/June 2012 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. For Examiner’s Use 1 2 Total

2 9700/33/M/J/12 © UCLES 2012 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 Question 1 and Question 2. • Plan your use of the time to make sure that you finish all the work that you would like to do. You will gain marks for recording your results according to the instructions. 1 When onion cells are placed into a sodium chloride solution with a higher concentration than the cells, water leaves the vacuoles and the cells become plasmolysed. In each concentration there will be cells which may show different states of plasmolysis. You are provided with four samples of onion tissue, each soaked in a different concentration of sodium chloride solution, labelled S1, S2, S3 and S4. labelled concentration of sodium chloride solution / mol dm–3 S1 0.8 S2 0.4 S3 0.2 S4 unknown You are required to: • observe and record the cells at different states of plasmolysis in S1, S2, S3 and S4 • use these results to answer (a)(iii) concerning the unknown concentration in S4. Fig. 1.1 will help you decide on the state of plasmolysis of the onion cells. no plasmolysis slight plasmolysis more plasmolysis complete plasmolysis Fig. 1.1 You are advised to read steps 1 to 10 before proceeding. Proceed as follows: 1. Label one dry and clean microscope slide S1 and put the slide on a paper towel. 2. Put a few drops of the sodium chloride solution from S1 onto the slide.

3 9700/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use 3. Remove a piece of the onion tissue from solution S1 and, using forceps or fingers, peel off the inner concave epidermis, as shown in Fig. 1.2. Fig. 1.2 4. Cut one piece of the epidermis that will fit under a coverslip. Replace the remaining epidermis into the solution in S1. 5. Place the epidermis in the sodium chloride solution on the slide as shown in Fig. 1.3. If the epidermis is folded, you may need to add more drops of sodium chloride solution so that it floats and uncurls. It is important to prevent the epidermis from drying out. epidermis solution slide paper towel Fig. 1.3 6. Cover the epidermis on the slide with a coverslip and use a paper towel to remove any excess liquid that is outside the coverslip. 7. Observe the states of plasmolysis of the cells using the microscope. 8. You may need to reduce the amount of light entering the microscope to observe the cells clearly. (a) (i) Describe how you will obtain accurate results to record the cells at different states of plasmolysis. … … …[1]

4 9700/33/M/J/12 © UCLES 2012 For Examiner’s Use (ii) Prepare the space below for recording your results. [4] 9. Record your results for S1 as you have described in (a)(i). 10. Repeat steps 1 to 9 with S2, S3 and S4. (iii) Use your results to complete the following statement. The sodium chloride concentration of the unknown sample, S4, is between … mol dm–3 and … mol dm–3. [1] (iv) Identify one significant source of error in using Fig. 1.1 to obtain your results. … … …[1] (v) Suggest how you would make three improvements to this investigation. … … … … … … …[3]

5 9700/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use A student investigated the effect of different sodium chloride concentrations on red blood cells. Red blood cells are destroyed (haemolysed) when placed in a sodium chloride solution with a lower concentration than the cells. The student’s results are shown in Table 1.1. Table 1.1 concentration of sodium chloride / × 10–2 mol dm–3 percentage of red blood cells destroyed 5.5 100 6.0 96 6.5 74 7.0 31 7.5 10 8.0 0 (b) (i) Plot a graph of the data shown in Table 1.1. [4] (ii) State the sodium chloride concentration at which 50% of the red blood cells are destroyed. Show on the graph how you obtained the concentration. [1] Sodium chloride concentration …[1]

6 9700/33/M/J/12 © UCLES 2012 For Examiner’s Use (iii) Explain what is happening between the red blood cells and the external solutions when 0 and 100% of red blood cells are destroyed. 0% red blood cells destroyed … … … 100% red blood cells destroyed … … …[3] [Total: 19]

7 9700/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use 2 Cell surface membranes are made up of proteins and phospholipids. The phospholipids form a bilayer. Egg yolk is a source of protein and oil is a source of lipids. These can be used to investigate the effect of mixing egg yolk with oil and with water. You are required to observe the effect of: • mixing oil and water • adding egg yolk to oil • mixing the egg yolk with oil and water. You are provided with: labelled contents Y egg yolk (in a syringe) O oil W distilled water You are advised to read steps 1 to 10 before proceeding. Proceed as follows: 1. Label a test-tube, P, and half-fill with water. 2. Use a syringe to put 5 cm3 of oil down the inside of test-tube P to form a layer on top of the water. 3. Repeat steps 1 and 2 with a test-tube, labelled Q. 4. As shown in Fig. 2.1, hold test-tube P near the top and rapidly move the test-tube five times to partly mix the oil and water. Fig. 2.1 5. Observe the contents of P and Q.

8 9700/33/M/J/12 © UCLES 2012 For Examiner’s Use (a) (i) Complete Fig. 2.2 to show your observations. Label and annotate P and Q in Fig. 2.2 to describe your observations. P Q Fig. 2.2 [1] 6. Hold the syringe, labelled Y, in the test-tube, labelled Q, so that you can release one drop close to the surface of the oil. 7. Observe the contents of Q. (ii) Complete Fig. 2.3 to show your observations. Label and annotate Q in Fig. 2.3 to describe your observations. Q (with egg yolk) Fig. 2.3 [3]

9 9700/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use 8. As shown in Fig. 2.4 put a bung in the test-tube labelled Q. Shake the test-tube vigorously to mix the oil and water thoroughly so that the egg yolk is broken up. bung direction of shaking Fig. 2.4 9. As shown in Fig. 2.4 put a bung in the test-tube labelled P. Shake the test-tube vigorously to mix the oil and water. 10. After two minutes, observe the contents of P and Q. (iii) Complete Fig. 2.5 to show your observations. Label and annotate P and Q in Fig. 2.5 to describe your observations. P Q (with egg yolk) Fig. 2.5 [2]

10 9700/33/M/J/12 © UCLES 2012 For Examiner’s Use Fig. 2.6 is a photomicrograph of normal human blood cells. magnification × 250 Fig. 2.6 (b) (i) Make a large drawing of three different types of blood cell. Mark on the photomicrograph the cells that you have drawn. [4]

11 9700/33/M/J/12 © UCLES 2012 [Turn over For Examiner’s Use (ii) Prepare the space below so that it is suitable for you to show the observable differences between the red blood cells and the white blood cells shown in Fig. 2.6. Record your observations in the space you have prepared. [5] Question 2 continues on page 12

12 9700/33/M/J/12 © UCLES 2012 For Examiner’s Use Fig. 2.7 is a photomicrograph of human red blood cells that have lost water through their surface membrane causing them to change shape. J K L M N magnification × 1430 Fig. 2.7 (iii) Use the magnification to calculate the mean actual diameter, in μm, of a crenated red blood cell using the labelled cells in Fig. 2.7. Draw the red blood cell, labelled J, and show where you measured this cell. You may lose marks if you do not show your working or if you do not use appropriate units. … μm [6] [Total: 21] Copyright Acknowledgements: Question 2, Fig. 2.6 ED RESCHKE/PETER ARNOLD INC./SCIENCE PHOTO LIBRARY Question 2, Fig. 2.7 ED RESCHKE/PETER ARNOLD INC./SCIENCE PHOTO LIBRARY 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 2012 question paper for the guidance of teachers 9700 BIOLOGY 9700/33 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, 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. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the May/June 2012 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 2012 9700 33 © University of Cambridge International Examinations 2012 Mark scheme abbreviations: ; separates marking points / alternative answers for the same point R reject A accept (for answers correctly cued by the question, or by extra guidance) 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 ora or reverse argument mp marking point (with relevant number) ecf error carried forward I ignore ACE Analysis, Conclusions and Evaluation (skills) MMO Manipulations, Measurement and Observation (skills) PDO Presentation of Data and Observations (skills)

Page 3 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (a) (ii) [4] table with all cells drawn AND heading (top row or left of recorded data column) concentration of sodium chloride solution/mol dm-3; mp1 Do not give mark if • units in cells of headed column (any correct heading – column or row) state(s) of plasmolysis; PDO recording 2 mp2 Do not give mark if • headings for method variables • records more than one cell for 0.8, 0.4. 0.2, or S1,S2,S3 AND S4 AND records state of plasmolysis for each cell or number of cells in each state; mp3 Do not give mark if • just record a single result for each solution or plasmolysed to non-plasmolysed has recorded for 0.8 or S1 in context of complete or more plasmolysis highest number of cells AND has recorded for 0.2 or S3 in context of no or slight plasmolysis highest number of cells; MMO collection 2 mp 4 Ignore • turgid or flaccid Expected Answers 1 (a) (i) [1] Idea of more than single cell or cells in field of view or that eyes can see or Idea of repeat or more readings / observations; MMO decision 1 Do not give mark if • ref. to observe over time or at different times • ref. to staining • any ref. to measuring

Page 4 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (a) (iii) [1] correct with their results (however shown e.g. % plasmolysed cells) and uses only • 0.8 to 0.4 • 0.4 to 0.2 • 0.2 to 0(.0)); ACE interpretation 1 Do not give mark if • no results for S4 • any other values (a) (iv) [max 1] cause of error WITH idea of error mp 1 (dependent variable) idea of state of plasmolysis cells on slide and in Fig 1.1 idea of difficult to judge / distinguish / see / observe or not enough states shown / only 4 or some cells between diagrams not the same or different; mp 2 qualitative; ACE interpretation MAX 1 Ignore • ref. to colour or stain • ref. to measurements

Page 5 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (a) (v) [max 3] mp 1 (independent variable) (concentration of sodium chloride) idea of use more concentrations or serial dilution; (dependent variable) more diagrams for more stages of plasmolysis; mp 2 Do not give mark if • to stain or colour repeat or replicate (in context of each solution); mp 3 Do not give mark if • more cells (standardised variables) idea of leave / soak (cells / onion) for longer or same time or until no further plasmolysis; mp 4 Do not give mark if • ref. to measure at different times use same onion or same part of onion or same age or fresh onion; mp 5 Do not give mark if • same cell ACE improvements MAX 3 mp 6 idea of same volume or e.g. with cm3 of solutions and measuring method; Do not give mark if • amount

Page 6 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 1 (b) (i) [4] mp 1 x-axis concentration (of) sodium chloride / NaCl solution / × 10–2 mol dm-3 AND y-axis percentage or % (of ) red blood cells destroyed; mp 2 scale as x-axis 0.5 to 2 cm labelled each 2 cm AND y-axis 20 to 2 cm labelled each 2 cm ; mp 3 correct plotting of • six points only • as small cross (does not go outside 2 mm × 2 mm square ) or dot (in circle) or cross in circle; Do not give mark if • plotted 50% with same as other points • blobs or dots alone • if blob in circle bigger than 1mm diameter PDO layout 4 mp 4 six plots with ruled lines exactly point to point or curve through 6 points AND (quality) smooth line less than 1 mm line thickness ; Do not give mark if • any extrapolation (b) (ii) [2] shows reading off at 50%; MMO collection 1 mp 1 correct reading from graph AND × 10–2 mol dm–3 ; ACE interpretation 1 mp 2 Can have mark if • line crosses at halfway between vertical lines then MUST read half square value e.g. 6.775 • line crosses nearer right vertical then can have only either half square value or value of right vertical • line crosses nearer left vertical then can have only either value of left vertical or half way value

Page 7 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (b) (iii) [3] Ignore ref. to plasmolysis, water potential, isotonic, hyper/hypotonic, haemolysis for any correct reference in context of water moving osmosis; mp 1 Must have • ref to only water moving correct idea of movement of water in 0% no net movement of water; mp 2 Do not give mark if • no movement of water ACE conclusion 3 mp 3 correct idea of movement of water in 100% idea of water moving into cells; Do not give mark if • ref. to no water out [Total: 19]

Page 8 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 2 (a) (i) [1] MMO decision 1 idea of describing difference in (P) (in top layer only) bubbles or drop(lets) or gas or air; Ignore • emulsion or immiscible Do not give mark for • bubbles either labelled or drawn on Q (a) (ii) [3] Ignore explanations e.g. hydrophobic molecules, etc. mp 1 identifies layers correctly (on top) oil AND (layer underneath) water; (Idea of position ) labels egg or yolk AND drawn or described egg / drop somewhere in bottom half of oil and top half of water or layer between oil and water; MMO decisions 2 mp 2 Ignore • emulsion or immiscible • additional drawings of egg e.g. on surface or tails into lower layer detail (anywhere) draws egg as drop or distinct rounded shape (not layer); PDO recording 1 mp 3 Ignore tails Do not give mark if • layer • If egg all at bottom of tube only happens if shaken

Page 9 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (a) (iii) [2] Ignore explanations precipitate suspensions solutions emulsions mp 1 (P) description P in (a) (iii) compared to P in (a) (i) looking for something other than labels of contents. idea of cloudy or hazy(ier) or milky or describes colour e.g. white or yellow or cream(y) or ref. to difference in bubbles described e.g. if no bubbles in P in (a)(i) then allow any bubbles labelled here or if bubbles in lower layer in P in (a)(i) then could have more bubbles in P here; MMO decision 2 mp 2 (annotated description (not contents) of • compare Q from (a)(ii) to Q in (a)(iii) (drawn and) labelled • egg / yolk at bottom of tube or in lower layer or lower half of test-tube • or labelled (meniscus curved in (a)(ii) to) meniscus flat(ter) or not / less curved • top layer foam or froth • bubbles • any valid ref. to cloudier or hazier or milkier or more white or turbid or dense • any valid ref. to different colours recorded; Do not give mark if • oil, water and yolk drawn as separate layers • labels only as mixture or emulsion

Page 10 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (b) (i) [4] PDO layout 1 mp 1 no shading or dashed line inside cell AND largest blood cell larger than 30mm AND clear, sharp, unbroken lines in all cell surface membranes drawn; Do not give mark if • less than three cell surface membranes or if any cell surface membrane has • drawn two lines • any ruled lines • any line more than 1 mm • any feathery or broken or dashed or gap • any ‘tail’ or overlap • drawn over the print of question on Fig.2.6 shows in any way three different types of cell AND draws both white blood cells with a nucleus and at least one red blood cell; mp 2 Ignore any labels for cells mp 3 drawn neutrophil larger than both of other two types of cells; MMO collection 3 mp 4 (in neutrophil) correct shape of nucleus AND (in other white blood cell) nucleus fills more than half the cell and positioned closer to or in contact with membrane on one side; (b) (ii) [5] PDO recording 1 mp 1 organise as a table with only three columns or rows separated by lines (no cells needed) Ignore numbered columns AND headings in any order only Do not give mark if divide wbc into 2 columns / rows red blood cells / rbc and white blood cells / wbc; AND third column / row contains examples of features only observable differences (at least two) recorded ; MMO decision 1 mp 1 Do not give mark if • any function or ref. to ‘not visible’ contents e.g. haemoglobin or organelles • two white blood cells given

Page 11 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 Max 3 feature red blood cells white blood cells mp 1 (size) small(er) larger; mp 2 (number) many or more few(er); mp 3 (nucleus presence) absent or no(ne) present or yes; mp 4 (cytoplasm) (surface) (granul(ar/les)) light(er) (red) or less dense smooth not rough no(one) / absent or agranular dark(er) (red) rough or textured yes / present or granular; mp 5 (grouping) idea of together or group or sticky or clump separate or not in groups; mp 6 (type) one or same two or different types; ACE interpretation 3 Ignore • functions • ref. to colour • shape of cell or nucleus • 3-D descriptions such as spherical, biconcave, ball, disc • tick and cross without a key • diagrams Can have difference on one side if e.g. use more or –er with vague answer in other column If no organisation then give mark only if difference in same sentence or following sentences Do not give mark if • for each feature the difference is not opposite each other • or e.g. red blood cell difference i difference ii white blood cell difference i difference ii

Page 12 Mark Scheme: Teachers’ version Syllabus Paper GCE AS/A LEVEL – May/June 2012 9700 33 © University of Cambridge International Examinations 2012 (b) (iii) [6] MMO collection 1 mp 1 shows at least one value for each of J, K, L, M and N or the same number of values from each cell; Ignore use of metres or µm MMO decision 1 mp 2 shows mm at least once on values 8 or higher; shows addition of at least five values AND shows division by number of values; mp 3 Can have • alternative signs for division Do not give mark for • Σx/n unless x and n have key shows at least one conversion of mm to µm by showing • multiplication by 1000 or 103 AND shows figure divided by1430; PDO display 2 mp 4 Can have • alternative signs for multiplication (or *) • or alternative signs for division Do not give mark if • metres anywhere • no mm anywhere PDO layout 1 mp 5 draws only one ‘bumpy / spiky’ cell with no shading; AND do not give mark if • any feathery or broken or dashed or gap or overlap or tail in the outline of cell • drawn over the print of question MMO collection 1 mp 6 shows any one measurement across a drawn cell (if more than one cell drawn then must be labelled J); Do not give mark if • cell has smooth shape e.g. oval, round etc. [Total: 21]