Biology 9700/35 October/November 2025: question paper and mark scheme

Question

Dialysis tubing is a partially permeable membrane. Some molecules such as glucose molecules can diffuse through pores in the membrane. You are required to investigate the diffusion of glucose through the pores in dialysis tubing using two different concentrations of glucose. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 R 20.0% glucose solution low 20 S 10.0% glucose solution low 20 G 1.0% glucose solution low 30 W distilled water low 100 Benedict’s Benedict’s solution harmful irritant 20 length of dialysis tubing D1 low – in distilled water length of dialysis tubing D2 low – in distilled water If any solution comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection. You will need to: • put two different concentrations of glucose solution into dialysis tubing surrounded by water • take a sample of the water surrounding the dialysis tubing • test the sample for the presence of glucose. * 0000800000003 * DFD 3 Carry out step 1 to step 10. step 1 Draw a mark 8 cm from the top of a large test‑tube, as shown in Fig. 1.1. 8 cm mark 8 cm from the top Fig. 1.1 step 2 Remove the dialysis tubing from beaker D1. Tie a knot in the dialysis tubing as close as possible to one end, so that the end is sealed. step 3 The whole length of the dialysis tubing needs to be separated to allow the tubing to be filled with solution. To do this, rub the whole length of the dialysis tubing gently between your finger and thumb. step 4 Put 10 cm3 of 20.0% glucose solution, R, into the open end of the dialysis tubing. step 5 Rinse the outside of the dialysis tubing by dipping it in the water in beaker D1. step 6 Put the dialysis tubing containing R into the large test‑tube and keep it in position using an elastic band as shown in Fig. 1.2. elastic band large test-tube dialysis tubing mark on test-tube 10 cm3 of glucose solution knot Fig. 1.2 * 0000800000004 * DFD 4 step 7 Put distilled water into the large test‑tube so that the top of the water is above the level of the glucose solution in the dialysis tubing. step 8 Start timing and leave the dialysis tubing in the distilled water for 15 minutes. step 9 Repeat step 1 to step 7 using the dialysis tubing in the container labelled D2 and the 10.0% glucose solution, S, instead of R. step 10 Start timing and leave the dialysis tubing in the distilled water for 15 minutes. While you are waiting, continue with preparing the glucose standards. Preparing glucose standards You will need to carry out a serial dilution of the 1.0% glucose solution, G, to reduce the concentration by half between each successive dilution. You will need to prepare four concentrations of glucose solution in addition to the 1.0% glucose solution, G. After the serial dilution is completed, you will need to have 10 cm3 of each concentration available to use. (a) (i) Complete Fig. 1.3 to show how you will prepare your serial dilution. Each beaker should have: • a labelled arrow to show the volume of glucose solution transferred • a labelled arrow to show the volume of distilled water, W, added • a label under the beaker to show the concentration of glucose solution. * 0000800000005 * DFD 5 0 cm3 of W 20 cm3 of 1.0% glucose solution, G 1.0% glucose solution Fig. 1.3 [3] * 0000800000006 * DFD 6 Carry out step 11 to step 19. step 11 Set up a boiling water‑bath ready for step 16. step 12 Prepare the concentrations of glucose solutions as shown in Fig. 1.3. step 13 Label 5 test‑tubes with the concentrations prepared in step 12. step 14 Put 1 cm3 of each glucose concentration into the appropriately labelled test‑tube. step 15 Put 1 cm3 of Benedict’s into each of the test‑tubes. Shake gently to mix. step 16 Put the test‑tube containing 1.0% glucose solution into the boiling water‑bath. Start timing. step 17 Record in (a)(ii) the time to the first colour change. If there is no colour change after 120 seconds, stop timing and record the time as ‘more than 120’. step 18 Remove the test‑tube from the boiling water‑bath. step 19 Repeat step 16 to step 18 with the other glucose concentrations. You will need the boiling water‑bath again in step 25. (ii) Record your results in an appropriate table. [5] * 0000800000007 * DFD 7 Carry out step 20 to step 23. step 20 Label a small test‑tube R1. step 21 After 15 minutes (step 8), put a 1 cm3 syringe into the water surrounding the dialysis tubing containing R, so that the end of the syringe is level with the mark on the test‑tube. Remove 1 cm3 from the water surrounding the dialysis tubing and put this into the test‑tube labelled R1. step 22 Label a small test‑tube S1. step 23 After 15 minutes (step 10), put a 1 cm3 syringe into the water surrounding the dialysis tubing containing S, so that the end of the syringe is level with the mark on the test‑tube. Remove 1 cm3 from the water surrounding the dialysis tubing and put this into the test‑tube labelled S1. You will determine the concentrations of glucose in R1 and S1 by: • carrying out the Benedict’s test on R1 and S1 • using your results to estimate the concentration of glucose in R1 and S1. Estimating the concentration of glucose in samples R1 and S1 Carry out step 24 to step 28. step 24 Put 1 cm3 of Benedict’s into the test‑tube labelled R1. Shake gently to mix. step 25 Put the test‑tube into the boiling water‑bath. Start timing. step 26 Record in (a)(iii) the time to the first colour change. If there is no colour change after 120 seconds, stop timing and record the time as ‘more than 120’. step 27 Remove the test‑tube from the boiling water‑bath. step 28 Repeat step 24 to step 27 with the test‑tube labelled S1. * 0000800000008 * DFD 8 (iii) Record your results for R1 and S1. result for R1 …… s result for S1 …… s [1] (iv) Use your results in (a)(ii) and (a)(iii) to estimate the percentage concentration of glucose in R1 and S1. percentage concentration of glucose in R1 = ……% percentage concentration of glucose in S1 = ……% [1] (v) Suggest a reason for the percentage concentrations of glucose estimated in R1 and S1 in (a)(iv). …… [2] (vi) Calculate the average rate at which the percentage concentration of glucose is increasing in the water surrounding the dialysis tubing containing R. Show your working and give your answer to two significant figures. [1] (vii) Suggest how you could modify this investigation to obtain a more accurate estimate for the concentration of glucose in sample R1. …… [2] * 0000800000009 * DFD 9 (viii) A possible source of error when carrying out step 21 is shown in Table 1.2. Complete Table 1.2 by stating the type of error as systematic or random, and the effect the error may have on the results. Table 1.2 systematic error source of error or effect on the results random error the line at 1.0 cm3 on the syringe used in step 21 actually measures a volume of 0.95 cm3 and not 1.0 cm3 [1] * 0000800000010 * DFD 10 (b) Fruits contain a range of naturally occurring sugars that make them taste sweet. These sugars include glucose, fructose and sucrose. Scientists measured the mass of these sugars in apple and pineapple. The results are shown in Table 1.3. Table 1.3 mass of sugar type of sugar / g per 100 g fruit apple pineapple glucose 2.3 1.3 fructose 6.9 2.3 sucrose 1.9 5.2 (i) Draw a bar chart of the data in Table 1.3 on the grid in Fig. 1.4. Use a sharp pencil. Fig. 1.4 [4] * 0000800000011 * DFD 11 (ii) Calculate the percentage difference in the mass of sucrose per 100 g of pineapple compared to the mass of sucrose per 100 g of apple. Show your working. percentage difference in the mass of sucrose = …… [1] [Total: 21] * 0000800000012 * DFD 12

Question

M1 is a slide of a stained transverse section through a plant stem. (a) (i) Draw a large plan diagram of the region on M1 indicated by the shaded area in Fig. 2.1. Use a sharp pencil. Use one ruled label line and label to identify the xylem. draw this region Fig. 2.1 [5] * 0000800000013 * DFD 13 (ii) Observe the xylem vessel elements in the stem on M1. Select a group of four adjacent xylem vessel elements. Each xylem vessel element must touch at least one other xylem vessel element. • 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] DFD 14 * 0000800000015 * DFD 15 (b) Fig. 2.2 is a photomicrograph of a stained transverse section of a stem from a different plant to M1. Fig. 2.2 Identify three observable differences, other than colour, between the stem section on M1 and the stem section in Fig. 2.2. Record these three observable differences in an appropriate table. [4] * 0000800000016 * DFD 16 (c) Fig. 2.3 shows a photomicrograph of a stage micrometer scale that is being used to calibrate an eyepiece graticule. One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines. The length of one division on the stage micrometer in Fig. 2.3 is 1.0 mm. stage micrometer 0 10 20 30 40 50 60 70 80 90 100 eyepiece graticule Fig. 2.3 (i) Calculate the actual length of one eyepiece graticule unit shown in Fig. 2.3. Give your answer in micrometres (μm). Show your working and give your answer to three significant figures. actual length of one eyepiece graticule unit = …… μm [3] * 0000800000017 * DFD 17 (ii) Fig. 2.4 is the same photomicrograph as that shown in Fig. 2.2. This was taken with the same microscope and the same lenses used to take the photomicrograph in Fig. 2.3. The eyepiece graticule has been placed across the length of a vascular bundle. 0 10 20 30 40 50 60 70 80 90 10 0 Fig. 2.4 Use the calibration of the eyepiece graticule unit from (c)(i) to calculate the actual length of the vascular bundle in Fig. 2.4. Show your working and use appropriate units. actual length of the vascular bundle = …… [2] [Total: 19] DFD 18 DFD 19 * 0000800000020 * DFD 20