Cambridge A Level Biology 9700 — 2019 May/June Paper 3 · Variant 5

1 Blood plasma contains proteins. The concentration of protein in blood plasma may change according to the health of a person. The concentration of protein in blood plasma can be measured to identify possible health problems. In this investigation you will be using protein solutions, P and U, instead of blood plasma. You will need to: • prepare a serial dilution of solution P • carry out the test for protein on each concentration of protein solution • carry out the test for protein on the unknown concentration of protein, U • estimate the concentration of protein in U. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 P 1% protein solution none 30 protein solution of unknown U none 10 concentration W distilled water none 100 5% potassium hydroxide harmful K 20 solution irritant C 0.15% copper sulfate solution none 20 If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. (a) You will need to: • make a serial dilution of 1.0% protein solution, P, which reduces the concentration by half between each successive dilution • prepare 10 cm3 of each concentration of protein solution. Fig. 1.1 shows the first two beakers you will use to make your serial dilution. (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 protein solution available for use in the investigation • use one arrow with a label, above the beaker, to show the volume and concentration of protein solution 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. 20 cm3 of ............................ 1.0% protein ............................ solution P 0 cm3 of W ............................ ...........................10 cm3 of 1.0% protein solution P ........................... to use ........................... ............................ ............................ ............................ [3] Fig. 1.1 Carry out the test for protein on the different concentrations of protein using step 1 to step 7. 1. Prepare the concentrations of protein solution as decided in (a)(i) and shown in Fig. 1.1. Use a glass rod to mix the protein solutions and water. 2. Label the test-tubes with the concentrations of the protein solutions 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 K 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. You will see a range of colours depending on the concentration of protein present. Table 1.2 shows the range of colours and the letters you will use to record your observations in (a)(ii). Table 1.2 colour letters to use very pale blue/colourless VP pale blue PB blue B pale purple PP purple P dark purple DP (ii) After step 7 you will see some of the colours in Table 1.2. Record the colours, in an appropriate table, by using the letters in Table 1.2. You may use the same letters for more than one test-tube. It may help to observe the colour with a piece of white card behind the test-tube. [5] You now need to estimate the concentration of U using your results. 8. Label a test-tube U and put 1 cm3 of U into this test-tube. 9. Repeat step 5 to step 7 then record the colour of U in (a)(iii). (iii) State the colour of U after step 7. .......................................................... [1] (iv) Complete Fig. 1.2 to show the position on the line of each of the percentage concentrations of protein solution in (a)(i). Using your results in (a)(ii) and (a)(iii), put the label U on Fig. 1.2 to show an estimate of the concentration of protein in U. 0.000 1.000 percentage concentration of protein Fig. 1.2 [1] (v) Suggest how you could change the independent variable to have more confidence in your estimate of the concentration of protein in U. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (vi) Suggest the apparatus that could be used to measure the concentration of protein in U more accurately. ..................................................................................................................................... [1] (b) The concentration of protein in blood plasma from five people with the same infection was measured for 11 days. The results are shown in Table 1.3. Table 1.3 time / days concentration of protein in blood plasma / g dm–3 person 1 person 2 person 3 person 4 person 5 mean 0 57 53 52 59 54 55 3 91 89 94 90 86 90 6 120 115 115 120 130 120 8 87 106 82 81 86 11 53 62 59 54 57 57 (i) Complete Table 1.3 by calculating the mean at 8 days. Space for working. [1] (ii) Plot a graph of the mean values shown in Table 1.3 on the grid in Fig. 1.3. Use a sharp pencil for drawing graphs. Fig. 1.3 [4] (iii) Explain, using your knowledge of the immune system, the increase in the concentration of protein in blood plasma between day 0 and day 6. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] [Total: 21]

Mark scheme: 1(a)(i) 1. 0.5%, 0.25%, 0.125% and 0.0625% (labels under the 2nd, 3rd, 4th and 5th beakers) ; 2. shows transfer of 10 cm3 from 1st beaker to 2nd beaker and 10 cm3 from 2nd beaker to 3rd beaker and 10 cm3 from 3rd beaker to 4th beaker ; 3. shows 10 cm3 of W added to 2nd, 3rd and 4th beakers ; 3 1(a)(ii) 1. heading for percentage concentration of protein ; 2. heading for colour ; 3. records results for at least four concentrations of protein ; 4. uses letters for the colours for all the concentrations ; 5. shows correct trend ; 5 1(a)(iii) states the colour for U ; 1 1(a)(iv) shows an estimate of the concentration of protein in U ; 1 1(a)(v) 1. makes a range of concentrations of protein solutions with narrower intervals ; 2. uses proportional dilution ; 2 1(a)(vi) colorimeter ; 1 1(b)(i) 84 ; 1 Question Answer Marks 1(b)(ii) 1. x-axis labelled as time / days + y-axis labelled as concentration of protein in blood plasma / g dm–3 ; 2. scale on x-axis is 2 to 2 cm, labelled at least every 2 cm + scale on y-axis is 20 to 2 cm, labelled at least every 2 cm ; 3. points plotted accurately with a small cross or a small dot in a circle ; 4. five points connected plot to plot or with a line of best fit ; 4 1(b)(iii) any 3 from: 1. the increase in the concentration of protein in blood plasma was caused by bacteria / bacterium / virus / foreign antigen ; 2. correct reference to plasma cells ; 3. production of antibodies ; 4. antibodies are proteins ; 3

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2 L1 is a slide of a stained transverse section through a plant leaf. You are not expected to be familiar with this specimen. The transverse section may contain more than one bulge, as shown in Fig. 2.1. largest bulge Fig. 2.1 (a) Select a field of view so that you can observe: • the largest bulge • the different tissues shown by the shaded area in Fig. 2.1. Use a sharp pencil for drawing. You are expected to draw the correct shape and proportions of the different tissues. (i) Draw a large plan diagram from the selected field of view which has: • part of the epidermis • the vascular tissue • any other observable tissues. Use one ruled label line and label to identify the upper epidermis. [6] (ii) Observe the upper epidermis of the leaf on L1. Select a line of four adjacent, touching cells that make up this tissue. Each cell must touch at least one of the other cells. Make a large drawing of this line of four cells. Use one ruled label line and label to identify the cell wall of one cell. [5] Fig. 2.2 is a photomicrograph of a stained transverse section through the leaf of a different type of plant. You are not expected to be familiar with this specimen. X magnification ×14 Fig. 2.2 (b) Use the magnification and the line X on Fig. 2.2 to calculate the actual depth of the midrib. Show all the steps in your working and use appropriate units. actual depth of midrib = ......................................................... [5]

Mark scheme: 2(a)(i) L1 is TS beech leaf 1. minimum size + at least two layers of tissue ; 2. draws only the midrib ; 3. correct proportion of the vascular area to the other tissues ; 4. shows subdivision of the vascular tissue ; 5. draws at least three layers of tissue ; 6. label line and label to identify the upper epidermis ; 6 2(a)(ii) 1. minimum cell size + lines thin and continuous ; 2. draws only four cells + each cell touching at least one other cell ; 3. draws at least one cell longer than it is deep ; 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) 1. measures depth of midrib along line X within range + units ; 2. shows conversion from mm to µm by multiplying by 1000 ; 3. shows division by 14 ; 4. correct answer ; 5. answer stated to the appropriate degree of accuracy ; 5 Question Answer Marks 2(c) records three observable differences between L1 and Fig. 2.3 ; ; ; e.g. L1 has more vascular bundles than Fig. 2.3 L1 has more midribs than Fig. 2.3 L1 has a thicker epidermis than Fig. 2.3 3

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