Cambridge A Level Biology 9700 — 2019 May/June Paper 3 · Variant 3

This document consists of 14 printed pages and 2 blank pages. DC (LEG/CGW) 156717/4 © UCLES 2019 [Turn over * 8 9 7 1 3 9 3 1 4 0 * BIOLOGY 9700/33 Paper 3 Advanced Practical Skills 1 May/June 2019 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. Cambridge Assessment International Education Cambridge International Advanced Subsidiary and Advanced Level For Examiner’s Use 1 2 Total

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3 9700/33/M/J/19 © UCLES 2019 [Turn over 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 the whole of Question 1 and Question 2. If you have enough time, think about how you can improve the confidence in your results, for example by recording one or more additional measurements. You will gain marks for recording your results according to the instructions. 1 Milk protein concentrates (MPCs) are used for manufacturing food products such as cheese and ice cream. Different types of milk contain different concentrations of protein. It is important for the food industry to know the concentration of protein in the milk used in the production of MPCs. The concentration of protein in milk can be measured using potassium hydroxide solution and copper sulfate solution. You will need to: • prepare a serial dilution of the proteins in the milk, M • carry out the test for protein on each concentration of milk. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 M 100% milk none 25 W distilled water none 100 P 5% potassium hydroxide solution harmful irritant 25 C 0.15% copper sulfate solution none 25 If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection.

4 9700/33/M/J/19 © UCLES 2019 You will need to make a serial dilution of 100% milk, M. The concentration of the milk should decrease by a factor of ten between each successive dilution. Fig. 1.1 shows the first two beakers you will use to make your serial dilution. (a)(i) Complete Fig. 1.1 by drawing as many extra beakers as you need for your serial dilution. For each beaker: • state, under the beaker, the volume and concentration of M available for use in the investigation • use one arrow with a label, above the beaker, to show the volume and concentration of M added to prepare the concentration • use another arrow with a label, above the beaker, to show the volume of W added to prepare the concentration.

5 9700/33/M/J/19 © UCLES 2019 [Turn over … … … … … … … … … 9 cm3 of 100% M to use 10 cm3 of 100% M 0 cm3 of W Fig. 1.1 [3]

6 9700/33/M/J/19 © UCLES 2019 Carry out the test for protein on different concentrations of milk using step 1 to step 9. The syringe labelled M must be used only for the 100% M. 1. Prepare the concentrations of milk as decided in (a)(i) and as shown in Fig. 1.1. Use a glass rod to mix the milk solution and water. 2. Label the test-tubes with the concentrations of milk as prepared in step 1. 3. Put 1 cm3 of each concentration into the appropriately labelled test-tube. 4. Label another test-tube 0.0% and put 1 cm3 of W into this test-tube. 5. Put 1 cm3 of P into each test-tube. Shake gently to mix. 6. Put 1 cm3 of C into each test-tube. Shake gently to mix. 7. Leave the test-tubes for at least 2 minutes. Shake gently to mix. Fig. 1.2 shows the key you need to use to record your results. A blue colour indicates that the concentration of protein is too low to be detected. Key colour symbol pink/purple ++++++ dark purple +++++ purple ++++ pale purple +++ blue ++ pale blue + Fig. 1.2 8. After step 7 observe the test-tubes. It may help to observe the colour with a piece of white card behind the test-tube. You may observe the same colour for more than one test-tube. 9. Record your results in (a)(ii) using the symbols shown in the key in Fig. 1.2.

7 9700/33/M/J/19 © UCLES 2019 [Turn over (ii) Record your results in an appropriate table for the known concentrations of milk. [4] You are provided with a different type of milk, X. The concentration of protein in X is unknown. You now need to: • carry out the test for protein on X using step 10 to step 12 • use your results in (a)(ii) to estimate the concentration of protein in X. 10. Label a test-tube with the letter X. 11. Put 1 cm3 of X into the test-tube labelled X. 12. Repeat step 5 to step 7, with X. (iii) After step 12, record your result for X using one of the symbols shown in the key in Fig. 1.2. result for X … [1] (iv) The 100% M contains 12 g of protein in 100 cm3. Using your results in (a)(ii) and (a)(iii), estimate the concentration of protein in X. Space for working concentration of protein in X = … g per 100 cm3 [1]

8 9700/33/M/J/19 © UCLES 2019 (v) Identify one significant source of error in the investigation described in step 1 to step 12. Explain why this is a source of error. source of error … explanation … … [1] (vi) Suggest three improvements to this investigation (step 1 to step 12) so that a more accurate estimate of the concentration of protein in X can be obtained. … … … … … … … [3] (b) A student carried out some research into the percentage mass of protein in the milk from different mammals. The results are shown in Table 1.2. Table 1.2 type of mammal percentage mass of protein buffalo (B) 4.05 camel (C) 2.35 horse (H) 0.80 goat (G) 3.60 sheep (S) 3.25

9 9700/33/M/J/19 © UCLES 2019 [Turn over Plot a bar chart of the data in Table 1.2 on the grid in Fig. 1.3. Use a sharp pencil for drawing graphs. Fig. 1.3 [4]

10 9700/33/M/J/19 © UCLES 2019 (c) Pepsin is an enzyme that breaks down proteins. A student investigated the effect of changing pH on the activity of pepsin. After mixing the milk, buffer and pepsin, the activity of pepsin was measured by recording the mass of protein remaining, in arbitrary units. All other variables were standardised. The student plotted a graph of the results, shown in Fig. 1.4. 10 8 6 4 mass of protein remaining / arbitrary units 2 0 2 3 4 pH of reaction 5 6 Fig. 1.4 (i) Describe the trend shown in Fig. 1.4. … … [1]

11 9700/33/M/J/19 © UCLES 2019 [Turn over (ii) Suggest an explanation for the results between pH2 and pH6. … … … … … … … [3] [Total: 21]

12 9700/33/M/J/19 © UCLES 2019 2 K1 is a slide of a stained transverse section through a plant stem. You are not expected to be familiar with this specimen. Use a sharp pencil for drawings. You are expected to draw the correct shape and proportions of the different tissues. (a) (i) Draw a large plan diagram of the transverse section through the plant stem on K1. Use one ruled label line and label to identify the epidermis. [5]

13 9700/33/M/J/19 © UCLES 2019 [Turn over (ii) Observe the central region of the plant stem on K1. Select four adjacent, touching cells. Each cell must touch at least two other cells. Make a large drawing of this group of four cells. Use one ruled label line and label to identify the cell wall of one cell. [5]

14 9700/33/M/J/19 © UCLES 2019 (b) Fig. 2.1 is a photomicrograph of a stained transverse section through a root of a different type of plant. You are not expected to be familiar with this specimen. Z 317 μm scale bar Fig. 2.1 ( i) Use the scale bar and the line Z on Fig 2.1 to calculate the actual width of the root. Show all the steps in your working and use appropriate units. actual width of the root = … [5]

15 9700/33/M/J/19 © UCLES 2019 (ii) Prepare an appropriate table for you to record observable differences between the stem on K1 and the root in Fig. 2.1. Record the observable differences in your table. [4] [Total: 19]

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This document consists of 8 printed pages. © UCLES 2019 [Turn over Cambridge Assessment International Education Cambridge International Advanced Subsidiary and Advanced Level BIOLOGY 9700/33 Paper 3 Advanced Practical Skills 1 May/June 2019 MARK SCHEME Maximum Mark: 40 Published 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 International will not enter into discussions about these mark schemes. Cambridge International is publishing the mark schemes for the May/June 2019 series for most Cambridge IGCSE™, Cambridge International A and AS Level and Cambridge Pre-U components, and some Cambridge O Level components.

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 2 of 8 Generic Marking Principles These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the specific content of the mark scheme or generic level descriptors for a question. Each question paper and mark scheme will also comply with these marking principles. GENERIC MARKING PRINCIPLE 1: Marks must be awarded in line with: • the specific content of the mark scheme or the generic level descriptors for the question • the specific skills defined in the mark scheme or in the generic level descriptors for the question • the standard of response required by a candidate as exemplified by the standardisation scripts. GENERIC MARKING PRINCIPLE 2: Marks awarded are always whole marks (not half marks, or other fractions). GENERIC MARKING PRINCIPLE 3: Marks must be awarded positively: • marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate • marks are awarded when candidates clearly demonstrate what they know and can do • marks are not deducted for errors • marks are not deducted for omissions • answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the question as indicated by the mark scheme. The meaning, however, should be unambiguous. GENERIC MARKING PRINCIPLE 4: Rules must be applied consistently e.g. in situations where candidates have not followed instructions or in the application of generic level descriptors.

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 3 of 8 GENERIC MARKING PRINCIPLE 5: Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may be limited according to the quality of the candidate responses seen). GENERIC MARKING PRINCIPLE 6: Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or grade descriptors in mind.

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 4 of 8 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

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 5 of 8 Question Answer Marks 1(a)(i) 1. labels under the 2nd, 3rd, 4th and 5th beakers 10(.00)%, 1(.00)%, 0.1(0)%, and 0.01% ; 2. shows transfer of 1 cm3 from 1st beaker to 2nd beaker and 1 cm3 from 2nd beaker to 3rd beaker and 1 cm3 from 3rd beaker to 4th beaker ; 3. shows 9 cm3 of W added to 2nd, 3rd and 4th beakers ; 3 1(a)(ii) 1. heading for percentage concentration of milk ; 2. heading for symbol or colour ; 3. records results for at least four concentrations of milk ; 4. shows correct trend ; 4 1(a)(iii) records result for X using one of the symbols in the key ; 1 1(a)(iv) estimates the concentration of protein in X ; 1 1(a)(v) identifies a source of error such as the difficulty in judging the exact shade of colour ; 1 1(a)(vi) 1. makes a range of concentrations of milk with narrower intervals ; 2. uses a colorimeter ; 3. carry out the testing of X at the same time as the test for proteins on each concentration of milk ; 3

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 6 of 8 Question Answer Marks 1(b) 1. x-axis labelled as type of mammal + y-axis labelled as percentage mass of protein ; 2. equal width of bars + scale on y-axis is 1 to 2 cm, labelled at least every 2 cm ; 3. correct plotting of five bars in the order in the table ; 4. five separate bars, drawn with vertical lines meeting horizontal lines exactly + labelled correctly ; 4 1(c)(i) describes trend as pH increases the percentage mass of protein remaining increases ; 1 1(c)(ii) any three from: 1. enzyme becomes denatured as pH increases (above pH2) ; 2. the shape of the active site changes ; 3. substrate cannot bind to the active site ; 4. fewer enzyme substrate complexes form ; 3

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 7 of 8 Question Answer Marks 2(a)(i) K1 is TS Erica stem 1. minimum size + at least two layers of tissue ; 2. draws whole stem + at least three layers of tissue ; 3. correct shape of stem ; 4. correct proportion of inner vascular area to the other tissues ; 5. label line and label to identify the epidermis ; 5 2(a)(ii) 1. minimum cell size + lines thin and continuous ; 2. draws only four cells + each cell touching at least two others ; 3. draws at least one cells with at least five sides ; 4. two lines drawn around each cell, three lines where cells touch ; 5. label line and label to identify the cell wall ; 5 2(b)(i) 1. measures scale bar within range ; 2. measures length of line Z within range ; 3. measurement of scale bar multiplied by 1000 + divided by 317 ; 4. shows measurement of line Z divided by the answer to mp3 ; 5. uses correct units ; 5

9700/33 Cambridge International AS/A Level – Mark Scheme PUBLISHED May/June 2019 © UCLES 2019 Page 8 of 8 Question Answer Marks 2(b)(ii) organises comparison into three columns with one column for features, one headed K1 and one headed Fig 2.1 ; records observable differences between K1 and Fig. 2.1 ; ; ; e.g. K1 has fewer layers of tissues than Fig. 2.1 K1 has a smooth, continuous outer layer while Fig. 2.1 has a rough outer layer cells of K1 are larger than the cells of Fig. 2.1 4