Cambridge A Level Biology 9700 — 2016 Feb/March Paper 3 · Variant 3

This document consists of 11 printed pages and 1 blank page. DC (ST/SW) 105818/5 © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 0 0 4 0 8 1 5 0 2 5 * BIOLOGY 9700/33 Advanced Practical Skills 1 February/March 2016 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. 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 an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. 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. For Examiner’s Use 1 2 Total

2 9700/33/F/M/16 © UCLES 2016 Before you proceed, read carefully through the whole of Question 1 and Question 2. Plan the use of the two hours to make sure that you finish all the work that you would like to do. If you have enough time, think about how you can improve the accuracy of your results, for example by obtaining and recording one or more additional measurements. You will gain marks for recording your results according to the instructions. 1 The concentration of protein in a person’s urine may be measured to identify certain health problems. You are required to: • prepare different concentrations of the protein solution, P • standardise and carry out the tests for protein concentration • record the results of tests for the known concentrations of protein and an unknown sample, U • estimate the concentration of protein in U. The protein concentration can be measured by using potassium hydroxide solution and copper sulfate solution. Fig. 1.1 shows the result of adding potassium hydroxide solution and copper sulfate solution to a sample containing protein. result (purple) add potassium hydroxide solution (colourless) then add copper sulfate solution (pale blue) sample containing protein Fig. 1.1

3 9700/33/F/M/16 © UCLES 2016 [Turn over Fig. 1.2 shows an example of a solution containing no protein (pale blue) and an example of a solution containing a high concentration of protein (dark purple), after testing. pale blue solution dark purple solution Fig. 1.2 You are provided with: labelled contents hazard volume / cm3 P 1.0% protein solution none 25 U sample of unknown protein concentration none 10 W distilled water none 25 K potassium hydroxide solution corrosive 15 C copper sulfate solution none 15 You are advised to wear suitable eye protection, especially when using the potassium hydroxide solution, K. If K comes into contact with your skin, wash off with cold water. (a) When carrying out a practical procedure, the hazards of using the solutions need to be considered. Then the level of risk needs to be assessed as low or medium or high. State the hazard with the greatest level of risk when using the solutions, then state the level of risk of the procedure: low or medium or high. hazard … level of risk … [1]

4 9700/33/F/M/16 © UCLES 2016 (b) (i) Table 1.1 shows how to make up two of the concentrations of protein solution you will use. Decide which concentrations of protein solution to prepare using simple dilution of the 1.0% protein solution, P. Complete Table 1.1 to show how you will prepare the other concentrations. Table 1.1 volume of 1.0% protein solution, P / cm3 volume of distilled water, W / cm3 percentage concentration of protein solution 5 0 0 5 1.0 0.0 [3] Proceed as follows: 1. Prepare the concentrations of protein solution, as shown in Table 1.1, in the beakers provided. 2. Put 1 cm3 of the 1.0% protein solution into a test-tube. 3. Put 1 cm3 of K into the same test-tube. Shake gently to mix. 4. Using the syringe labelled C, put 1 cm3 of C into the same test-tube. Shake gently to mix. You are required to standardise this test (step 2 to step 4) to be able to use the results to estimate the concentration of protein in U. (ii) State which variable you will need to standardise when testing the other protein solutions and U. …[1] Read step 5 to step 8 before proceeding. 5. Carry out the standardised test for each of the protein solutions prepared in step 1. 6. Record your observations of the colour of each solution in (b)(iii).

5 9700/33/F/M/16 © UCLES 2016 [Turn over 7. In a test-tube rack, put the test-tubes in order of palest blue to darkest purple. 8. Record in (b)(iii) each colour as a number using the scale shown in Fig. 1.3. 0 1 2 3 4 5 6 7 8 9 10 palest blue darkest purple Fig. 1.3 (iii) Prepare the space below and record your observation for each test-tube as a colour and its number, using the scale in Fig. 1.3. [5] 9. Carry out the standardised test with a sample of U. (iv) Using the scale in Fig. 1.3 and the result for this test of U, state the number that represents the colour when compared with the results in (b)(iii). number for U … Use your results to estimate the concentration of protein in U. estimated concentration of protein in U … [1] (v) Identify one significant source of error when estimating the concentration of protein in U. … …[1]

6 9700/33/F/M/16 © UCLES 2016 (c) Scientists may use another method to measure the protein concentration in urine samples. A sample of urine is put into a test-tube and an equal volume of reagent X is added. When the mixture is shaken, a cloudy precipitate of protein forms. (i) State two of the variables which need to be standardised when using this method to compare different samples of urine. Describe a method which can be used to standardise each of these variables. variable 1 … description … … … variable 2 … description … … … [3] A colorimeter can be used to measure the quantity of light absorbed (absorbance) by a solution. After adding reagent X, a scientist used a colorimeter to obtain the absorbance of: • six solutions of known protein concentration • a urine sample (of unknown protein concentration). A calibration graph was drawn by plotting the absorbance against the known concentrations of protein in the six solutions. The graph can be used to estimate the concentration of protein in the urine sample. Table 1.2 shows the results for the absorbance of solutions of known protein concentration. Table 1.2 protein concentration / µg cm–3 absorbance 0 0.00 100 0.06 200 0.36 450 0.28 760 0.47 900 0.52

7 9700/33/F/M/16 © UCLES 2016 [Turn over You are required to use a sharp pencil for graphs. (ii) Plot a graph of the data shown in Table 1.2. [4] (iii) Draw a circle on the graph to show the anomalous result. [1] (iv) Use your graph to estimate the concentration of protein in a urine sample with an absorbance of 0.49. Show on your graph how you estimated the concentration of protein. concentration of protein … [2] [Total: 22]

8 9700/33/F/M/16 © UCLES 2016 2 You are provided with two samples of onion that have been kept in two different solutions, S1 or S2. You are required to: • make slides of the inner epidermis of onions that have been kept in S1 and S2 • observe and draw two cells from each epidermis. 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 S1 onto the slide. 3. Remove a piece of the onion from S1 and, using forceps or fingers, peel off the inner epidermis, as shown in Fig. 2.1. inner epidermis Fig. 2.1 4. Cut one piece of the inner epidermis that will fit under a coverslip. Put the remaining inner epidermis back into S1. 5. Place the inner epidermis on the slide as shown in Fig. 2.2. If the epidermis is folded, you may need to add more drops of S1 so that it floats and uncurls. Note: It is important to prevent the epidermis from drying out, so add more drops of S1 if needed. epidermis solution slide paper towel Fig. 2.2 6. Cover the epidermis with a coverslip and use a paper towel to remove any excess solution that is outside the coverslip. 7. Repeat step 1 to step 6 using the piece of onion in S2 and mount the piece of inner epidermis in S2, on a slide labelled ‘S2’.

9 9700/33/F/M/16 © UCLES 2016 [Turn over (a) Use the microscope to select an area of cells on each of the slides S1 and S2 that shows the effect of keeping the epidermis in the solution. Adjust the amount of light entering the microscope to observe cells clearly. You are required to use a sharp pencil for drawings. (i) Draw two adjacent (touching) cells from each slide. Use one ruled label line and label to identify the cell wall of one of the cells. two cells from S1 two cells from S2 [5] (ii) Using your observations of the cells drawn in (a)(i), state which of the solutions, S1 or S2, had a more negative water potential than the onion cells. solution … Explain the reason for your answer. … … … … … [3]

10 9700/33/F/M/16 © UCLES 2016 Fig. 2.3 is a photomicrograph of human red blood cells that have been kept in a solution. This has caused most of the cells to change shape (become crenated). D Z E H G F magnification ×1430 Fig. 2.3 (b) (i) Draw the cells labelled D and Z. cell D cell Z [3]

11 9700/33/F/M/16 © UCLES 2016 (ii) Annotate the drawings in (b)(i) to describe one observable difference between cell D and cell Z. [1] (iii) Suggest one reason for the observable difference between cell D and cell Z. … …[1] (c) (i) Use the magnification to find the actual diameter, in μm, of the cells labelled D, E, F, G and H in Fig. 2.3. For each cell, measure the diameter at the position shown by the line. You may lose marks if you do not show your working. D … μm, E… μm, F… μm, G… μm, H… μm [3] (ii) Using the actual diameters calculated in (c)(i), calculate the mean actual diameter of a crenated red blood cell. You may lose marks if you do not show your working or if you do not use appropriate units. mean actual diameter …[2] [Total: 18]

12 9700/33/F/M/16 © UCLES 2016 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. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. 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.

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the March 2016 series 9700 BIOLOGY 9700/33 Paper 3 (Advanced Practical Skills), 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 should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the March 2016 series for most Cambridge IGCSE® and Cambridge International A and AS Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – March 2016 9700 33 © Cambridge International Examinations 2016 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 accepted) 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 AVP Alternative valid point (examples given as guidance)

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – March 2016 9700 33 © Cambridge International Examinations 2016 1 (a) (hazard and level of risk) corrosive + medium or high ; [1] (b) (i) 1 at least four percentage concentrations of protein ; 2 volumes of P for three percentage concentrations of protein ; 3 volumes of P and W for three percentage concentrations of protein make 5 cm3 ; [3] (ii) volume of, sample / protein solution, to test or volume of reagents (potassium hydroxide solution / K and copper sulfate solution / C) ; [1] (iii) 1 table drawn + heading for percentage concentration of protein ; 2 headings for colour / observation + (scale) number ; 3 records results for at least four concentrations of protein ; 4 appropriate result for 1% protein solution ; 5 appropriate result for solution with lowest concentration of protein ; [5] (iv) stated protein concentration of U matched to number and results in (b)(iii) ; [1] (v) appropriate error identified ; e.g. difficulty of judging colour [1] (c) (i) 1 two correct variables ; ; e.g. volume of urine sample + volume of reagents (K and C) 2 shaking or mixing of solutions 3 correct description of any one method ; e.g. using syringe to standardise volume stated method to standardise mixing [3] (ii) 1 (x-axis label) protein concentration / µg cm–3 + (y-axis label) absorbance ; 2 (scale on x-axis) 200 to 2 cm, labelled at least each 2 cm + (scale on y-axis) 0.2 to 2 cm, labelled at least each 2 cm ; 3 correct plotting of six points as small crosses or dots in circles ; 4 six plots + thin smooth line of best fit to zero or ruled lines exactly point to point ; (not including anomalous result) [4] (iii) circle around plotted point on graph at 200, 0.36 ; [1] (iv) 1 shows how to read off concentration of protein from graph at 0.49 ; 2 correctly estimates concentration of protein + µg cm–3 ; [2]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – March 2016 9700 33 © Cambridge International Examinations 2016 2 (a) (i) 1 sharp and continuous line for outer walls of cells ; 2 size at least 50 mm across largest cell + no shading ; 3 two touching cells drawn for each slide ; 4 both cells in S1 drawn with cell surface membrane pulled away from cell wall ; 5 label line + label to cell wall of one of the cells ; [5] (ii) 1 (solution) S1 ; 2 correct explanation in terms of water potential ; 3 direction of water movement + cell (surface) membrane away from cell wall / plasmolysis ; [3] (b) (i) 1 cell D: wavy outline ; 2 cell D: 9–11 folds ; 3 cell Z: smooth outline with sharp, continuous line ; [3] (ii) cell D annotation: wavy / folded, cell (surface) membrane or cell Z annotation: cell (surface) membrane, smooth / not folded ; [1] (iii) (cell D and cell Z) have different water potentials or cell D has higher water potential than (surrounding) solution or cell Z has same water potential as (surrounding) solution ; [1] (c) (i) 1 correct measurements for all cells + recorded as whole numbers (or to 0.5) + units in mm ; 2 (for all five cells) shows division by 1430 ; 3 (for all five cells decides on correct conversion of mm to µm) multiplies by 1000 ; [3] (ii) 1 shows addition of measurements from (c)(i) + division by 5 ; 2 answer shown to whole number or to appropriate accuracy + µm ; [2]