Cambridge A Level Biology 9700 — 2023 May/June Paper 3 · Variant 5

1 You will be investigating the effect of salt concentration on the movement of water in potatoes. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 P 5 lengths of potato none – W distilled water none 150 S 1 mol dm–3 salt solution none 150 It is recommended that you wear suitable eye protection. (a) You will need to make different concentrations of salt solution using proportional dilution of the 1.00 mol dm–3 salt solution, S. You will need to prepare 40 cm3 of each concentration. Table 1.2 shows two of the concentrations you will use. Decide which other concentrations of salt solution you will use. (i) Complete Table 1.2 to show how you will prepare the other concentrations. Table 1.2 final concentration of volume of S volume of distilled water, salt solution / cm3 W / mol dm–3 / cm3 1.00 40 0 0.00 0 40 [2] Carry out step 1 to step 11. step 1 Prepare the concentrations of salt solution, as shown in Table 1.2, in the beakers provided. step 2 Cut 10 discs of potato for each of the concentrations prepared in step 1. Each disc should be approximately 3 mm thick. step 3 Place 10 discs in a line as shown in Fig. 1.1. centimetre 1 2 3 4 5 6 7 8 9 not to scale discs Fig. 1.1 step 4 Measure the total length of the 10 discs and record this value in 1(a)(ii). step 5 Put the 10 discs into the beaker containing 1 mol dm–3 salt solution. step 6 Repeat step 3 to step 5 with the other discs and the salt solutions you prepared in step 1. step 7 Start timing and leave for 30 minutes. Use this time to continue with other parts of Question 1. step 8 After 30 minutes (step 7), discard the 1 mol dm–3 salt solution from around the discs and tip the discs onto some paper towel. step 9 Place the 10 discs in a line as in Fig. 1.1 and measure their total length. Record this value in 1(a)(ii). step 10 Repeat step 8 and step 9 for the other salt concentrations. step 11 Calculate the change in length for each line of 10 discs. (ii) Record your results in an appropriate table, including raw results and processed results. [5] (iii) Explain your results for the 0.0 mol dm–3 salt solution (distilled water). ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iv) Suggest why a line of 10 discs was measured instead of a single disc. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (v) Identify one significant source of error in this investigation. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Use your results to estimate a salt concentration where there is no net movement of water into or out of the potato. salt concentration .......................................... mol dm–3 [1] (vii) Describe two improvements to your procedure that would make the estimate in 1(a)(vi) more accurate. 1 ........................................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (b) The salt content of unprocessed food was measured. The values are shown in Table 1.3. Table 1.3 salt content of food type unprocessed food / mg per 100 g food potatoes (P) 10.0 tuna (T) 40.0 bran (B) 25.0 chicken (C) 50.0 salmon (S) 95.0 (i) Plot a bar chart of the data shown in Table 1.3 on the grid in Fig. 1.2. Use a sharp pencil. [4] Fig. 1.2 The salt content of the same foods that had been processed was also measured. The values are shown in Table 1.4. Table 1.4 salt content of food type processed food / mg per 100 g food potatoes (P) 200.0 tuna (T) 300.0 bran (B) 1000.5 chicken (C) 350.5 salmon (S) 1800.0 (ii) Calculate the percentage increase in salt content when salmon is processed. Show your working and write your answer to two significant figures. increase in salt content ..................................................... % [2] (iii) State the independent variable in this study. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 21]

Mark scheme: 1(a)(i) 1 at least 3 additional concentrations ; 2 volumes of S and W add up to 40 ; 2 1(a)(ii) 1 heading for concentration of salt and mol dm-3 ; 2 headings for initial length and final length and mm ; 3 records result for each concentration prepared ; 4 records changes in length ; 5 records correct trend, lowest concentration has greatest increase ; 5 1(a)(iii) 1 0.0 mol dm-3 salt solution has higher water potential than potato cells ; 2 water moves into potato cells by osmosis ; 2 1(a)(iv) measuring the change in length of a single disc more inaccurate than measuring a line of 10 discs ; 1 1(a)(v) not all the discs were exactly 3 mm in thickness ; 1 1(a)(vi) correct estimate of salt concentration where there was no net movement of water into or out of the potato ; 1 1(a)(vii) 1 using smaller intervals of salt concentrations around the value of the candidates’ estimate ; 2 use a more precise method of cutting discs ; 2 1(b)(i) 1 labels on x-axis: food type and labelled P, T, B, C, S and label on y-axis: salt content of unprocessed food / mg per 100 g food ; 2 even width of bars and scale on y-axis: 20 to 2 cm, labelled at least every 2 cm ; 3 correct plotting of 5 bars ; 4 separate bars drawn with vertical lines and meeting horizontal lines exactly ; 4 1(b)(ii) 1 shows (1800 – 95) divided by 95 and multiplied by 100 ; 2 correct answer to two significant figures ; 2 1(b)(iii) food type or processed and unprocessed food ; 1

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2 M1 is a slide of a stained transverse section through a plant leaf. (a) (i) Draw a large plan diagram of the region of the leaf on M1 indicated by the shaded region in Fig. 2.1. Use a sharp pencil. draw this region Fig. 2.1 Use one ruled label line and label to identify the lower epidermis. [5] (ii) Observe one of the central vascular bundles of the leaf on M1. Select a group of four adjacent xylem vessel elements. Each xylem vessel element must touch at least two other xylem vessel elements. • Make a large drawing of this group of four xylem vessel elements. • Use one ruled label line and label to identify the wall of one xylem vessel element. [5] (b) Fig. 2.2 shows a photomicrograph of a stage micrometer scale that is being used to calibrate an eyepiece graticule. The length of one division on this stage micrometer is 1 mm. stage micrometer 0 10 20 30 40 50 60 70 80 90 100 eyepiece graticule Fig. 2.2 (i) Use Fig. 2.2 to calculate the actual length of one eyepiece graticule unit. Show your working and include appropriate units. actual length = ......................................................... [3]

Mark scheme: 2(a)(i) 1 uses most of the available space and draws minimum number of tissues ; 2 draws only the midrib and no cells ; 3 shows a V-shaped midrib ; 4 shows a large central vascular bundle below a distinct area of cells ; 5 label line and label to the lower epidermis ; 5 2(a)(ii) 1 uses most of the available space and lines continuous, thin and sharp ; 2 each of four xylem vessel elements touching at least two other vessel elements ; 3 draws two lines around each cell and three lines where cells meet ; 4 correct shape of xylem vessel elements, angular with straight walls ; 5 label line and label to the wall of one xylem vessel element ; 5 2(b)(i) 1 states correct number of graticule units per 1 mm division (19) ; 2 shows one divided by 19 ; 3 correct answer and units ; 3 2(b)(ii) 1 states correct number of graticule units across leaf depth (38) ; 2 correct calculation and answer to two significant figures ; 2 2(b)(iii) suggests a correct function of the large air spaces as being related to gases in the leaf or buoyancy ; 1 2(b)(iv) any three from: feature M1 Fig. 2.3 epidermis thick angular ; palisade mesophyll present no distinct palisade mesophyll ; stomata present absent ; vascular bundle central in midrib no central vascular bundle ; 3

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