Cambridge A Level Biology 9700 — 2024 May/June Paper 3 · Variant 5

1 Beetroot is a root vegetable that contains a red pigment in its cells. When beetroot is put in ethanol, the red pigment is released from the beetroot tissue and the ethanol changes to a red colour. You will investigate the effect of different concentrations of ethanol on the release of red pigment from beetroot tissue. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 4 beetroot cylinders in B none - distilled water flammable E 50% ethanol 100 harmful W distilled water none 300 If any solution comes into contact with your skin, wash off immediately under cold water. You should wear suitable eye protection. You will need to make different concentrations of ethanol, using proportional dilution of the 50% ethanol, E. You will need to prepare 20 cm3 of each concentration, using E and W. Table 1.2 shows how to prepare two of the concentrations of ethanol you will use. Decide which other concentrations of ethanol you will use. (a) (i) Complete Table 1.2 for the other concentrations you will use. Table 1.2 percentage concentration volume of E volume of W of ethanol / cm3 / cm3 50 20.0 0.0 0 0.0 20.0 [2] Carry out step 1 to step 14. step 1 In the beakers provided, prepare the concentrations of ethanol as shown in Table 1.2. step 2 Label large test-tubes with the concentrations of ethanol stated in Table 1.2. step 3 Put 10 cm3 of each concentration of ethanol into the appropriately labelled large test-tubes. step 4 Cut the beetroot cylinders into 2 mm thick discs, using a single-edged blade. You will need 10 discs for each concentration of ethanol. step 5 Put the discs into a small beaker and cover with distilled water, W. step 6 Stir with a glass rod. step 7 Pour the surrounding liquid into the beaker labelled For waste. step 8 Blot the discs on a paper towel to remove excess water. step 9 Put 10 discs into each of the large test-tubes. Start timing and leave for 10 minutes. While you are waiting use your time to continue with other parts of Question 1. step 10 Label small test-tubes with the ethanol concentrations shown in Table 1.2. step 11 After 10 minutes (at the end of step 9) stir the contents of each large test-tube. step 12 Pour the liquid from each large test-tube into the appropriately labelled small test-tube. The discs should remain in the large test-tubes. Fig. 1.1 shows the key you need to use to record your results. Key no colour + very pale red (lowest intensity) ++ +++ ++++ +++++ deep red (highest intensity) ++++++ Fig. 1.1 step 13 Observe the colour of the liquid in each small test-tube. step 14 Record your observations in (a)(ii) using the symbols shown in the key in Fig. 1.1. (ii) Record your observations in an appropriate table. [5] (iii) Describe the trend in your results. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iv) With reference to your results in (a)(ii), explain the effect of ethanol on cell membranes. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (v) State the dependent variable in this investigation. ..................................................................................................................................... [1] (vi) State one variable that was standardised and describe how it was standardised. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (vii) Identify one source of error in this investigation. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (viii) Describe how you would modify the procedure to investigate the effect of temperature on the permeability of beetroot cell membranes. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) Researchers investigated the effect of drinking beetroot juice on blood pressure. Two groups of people were used in the investigation. • One group was given 500 cm3 of beetroot juice to drink. • A control group was given 500 cm3 of water to drink. • The mean blood pressure of each group was measured at intervals. • The difference in mean blood pressure between the two groups was calculated. Table 1.3 shows the results of the investigation. Table 1.3 time after drinking difference in mean blood pressure / minutes compared to control group / kPa 0 0.0 25 – 0.28 80 – 0.57 125 – 0.92 160 –1.33 220 – 0.87 (i) Plot a graph of the data shown in Table 1.3 on the grid in Fig. 1.2. Fig. 1.2 [4] (ii) After 100 minutes, the mean blood pressure for the control group was 15.79 kPa. Use your graph in Fig. 1.2 to calculate the mean blood pressure after 100 minutes for the group that was given beetroot juice. Show your working. mean blood pressure after 100 minutes = .................................................. kPa [2] [Total: 22]

Mark scheme: 1(a)(i) 1 states at least three additional concentrations of ethanol ; 2 states the correct volumes of ethanol and water to make 20 cm3 for each concentration ; 2 1(a)(ii) 1 heading for independent variable: percentage concentration of ethanol ; 2 heading for dependent variables: colour intensity / symbol ; 3 states results for all the concentrations made ; 4 correct trend for results: the highest concentration has a more intense colour than lowest concentration ; 5 records results using scale provided ; 5 1(a)(iii) describes the trend to match candidate’s results ; 1 1(a)(iv) 1 (ethanol) denatures the proteins in the cell surface membrane ; 2 (ethanol) dissolves the phospholipids (and cholesterol) ; 3 causing, increase in permeability / increase in fluidity ; 3 1(a)(v) intensity of colour ; 1 1(a)(vi) states one variable that was standardised and a description of how it was standardised ; e.g. amount of beetroot and cutting 10 discs of beetroot time the beetroot was left in the ethanol for and a stated time (e.g. 10 minutes) ; 1 1(a)(vii) states a suitable source of error ; e.g. difficulty of judging the final colour of the solution 1 1(a)(viii) uses one stated concentration of ethanol ; states using at least five different temperatures ; 2 1(b)(i) 1 label on x-axis: time after drinking / minutes and label on y-axis: difference in mean blood pressure compared to control group / kPa ; 2 scale on x-axis: 50 to 2 cm and scale on y-axis: 0.2 to 2 cm and labelled at least every 2 cm ; 3 correct plotting of all six points using small crosses or dots in circles ; 4 points joined with a smooth, thin line and joined point-to-point through all the points ; 4 Question Answer Marks 1(b)(ii) 1 shows interpolation on graph at 100 minutes ; 2 shows 15.79 (mean blood pressure for control group) minus the value from interpolation ; 2

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2 N1 is a slide of a stained transverse section through a plant leaf. (a) (i) Draw a large plan diagram of part of the leaf section on N1 to show the different tissues. The section that you choose to draw should include four vascular bundles. Use one ruled label line and label to identify one vascular bundle. [5] (ii) Observe the cells in the epidermis of the leaf on N1. Select two guard cells and two adjacent epidermal cells. Each cell must touch at least one other cell. • Make a large drawing of this line of four cells. • Use one ruled label line and label to identify the cell wall of one guard cell. [5] (b) Fig. 2.1 is a photomicrograph of a transverse section of a leaf from a different type of plant. A B scale bar 100μm Fig. 2.1 (i) Identify three observable features, other than colour, that are different between the leaf section on N1 and the leaf section in Fig. 2.1. Record these three observable features in an appropriate table.

Mark scheme: 2(a)(i) 1 uses most of the available space and no shading ; 2 draws the draws at least four vascular bundles and no cells included ; 3 draws the correct number of tissue layers ; 4 draws at least one large air space ; 5 label line and label to one vascular bundle; 5 2(a)(ii) 1 uses most of the available space and lines continuous, thin and sharp ; 2 draws only four cells and each cell touches at least one other cell ; 3 two lines around each cell and three lines where cells touch ; 4 both guard cells smaller than adjacent cells ; 5 label line and label to cell wall of one guard cell ; 5 2(b)(i) records only observable differences ; three correct differences between N1 and Fig. 2.1 ;;; e.g. feature N1 Fig. 2.1 shape of section spiral angular number of vascular bundles more fewer position of vascular bundles peripheral / close to edges central palisade mesophyll layer thin thick / bilayer 4 Question Answer Marks 2(b)(ii) 1 correct measurements of the scale bar and the line A–B ; 2 shows the length of A–B divided by the length of the scale bar and multiplied by 100 3 correct answer and uses appropriate units ; 3 2(b)(iii) correct answer and recorded to two significant figures ; 1

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