Biology 9700/33 October/November 2025: question paper and mark scheme

Question

Dialysis tubing is a partially permeable membrane. Glucose molecules can diffuse through the dialysis tubing. You are required to investigate the diffusion of glucose across dialysis tubing. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 G 20.0% glucose solution low 50 W distilled water low 200 Benedict’s Benedict’s solution harmful irritant 40 length of dialysis tubing D 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 glucose solution into dialysis tubing surrounded by water • take samples of the water surrounding the dialysis tubing • test for the presence of glucose in each sample of water. * 0000800000003 * DFD 3 Carry out step 1 to step 11. 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 D. 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 gently between your finger and thumb. step 4 Put 10 cm3 of 20.0% glucose solution, G, 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 D. step 6 Put the dialysis tubing containing G 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. You are required to take samples of the water surrounding the dialysis tubing every 5 minutes for 15 minutes. You will collect three samples. step 9 Label three test-tubes with the times the samples of water will be taken (5, 10 and 15). step 10 After 5 minutes (step 8), put a 1 cm3 syringe into the water surrounding the dialysis tubing 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 5. Repeat this action to remove another 1 cm3 from the water surrounding the dialysis tubing and put this into the test-tube labelled 5. The test-tube labelled 5 will now contain a 2 cm3 sample. Do not stop timing. step 11 Repeat step 10 at 10 minutes and at 15 minutes using the appropriately labelled test-tubes. You need to carry out a dilution of the 20.0% glucose solution, G, to make a 1.0% glucose solution. You will need 20 cm3 of this 1.0% glucose solution. Complete Table 1.2 to show the volume of distilled water, W, you will use to make 20 cm3 (a) (i) of a 1.0% glucose solution. Table 1.2 volume of 20.0% glucose solution, G volume of distilled water, W / cm3 / cm3 1 …… [1] step 12 Prepare the 1.0% glucose solution as shown in Table 1.2. You will need to carry out a serial dilution of the 1.0% glucose solution you have prepared in step 12 as shown in Fig. 1.3. You must 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 from step 12. After the serial dilution is completed, you will need to have 10 cm3 of each concentration available to use. * 0000800000005 * DFD 5 (ii) 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. 1.0% glucose solution 0.5% glucose solution 0.25% glucose solution 0.125% glucose solution 0.0625% glucose solution Fig. 1.3 [2] * 0000800000006 * DFD 6 step 13 Set up a boiling water-bath ready for step 18 and step 22. step 14 Prepare the concentrations of glucose solution as shown in Fig. 1.3. step 15 Label 5 test-tubes with the concentrations of glucose solution shown in Fig. 1.3. step 16 Put 2 cm3 of the 1.0% glucose solution into the appropriately labelled test-tube. (iii) You are required to carry out the Benedict’s test on the glucose solutions that you have prepared in step 14. State the volume of Benedict’s solution you will use for each reducing sugar test. Explain why you have selected this volume. volume of Benedict’s solution …… cm3 explanation …… [1] step 17 Put the volume of Benedict’s solution stated in (a)(iii) into the test-tube labelled 1.0%. Shake gently to mix. step 18 Put this test-tube into the boiling water-bath and record in Table 1.3 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 19 Remove the test-tube from the boiling water-bath. step 20 Repeat step 16 to step 19 using 2 cm3 of each of the other concentrations of glucose solution. (iv) Complete Table 1.3 to record your results. Table 1.3 percentage concentration of glucose 1.0 0.5 0.25 0.125 0.0625 [1] * 0000800000007 * DFD 7 You are required to carry out the Benedict’s test on the three samples collected from the water surrounding the dialysis tubing (5, 10 and 15). step 21 Put the volume of Benedict’s solution stated in (a)(iii) into the test-tube labelled 5. Shake gently to mix. step 22 Put this test-tube into the boiling water-bath and record in (a)(v) 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 23 Remove the test-tube from the boiling water-bath. step 24 Repeat step 21 to step 23 for the other samples (10 and 15). (v) Record your results in an appropriate table. [4] (vi) State one source of error when carrying out the Benedict’s test. …… [1] (vii) Use your results in (a)(iv) and (a)(v) to estimate the percentage concentration of glucose in the samples taken at 5, 10 and 15 minutes. percentage concentration of glucose in sample 5 = …… percentage concentration of glucose in sample 10 = …… percentage concentration of glucose in sample 15 = …… [1] * 0000800000008 * DFD 8 (viii) Suggest a reason for the percentage concentrations of glucose estimated in (a)(vii). …… [1] * 0000800000009 * DFD 9 Question 1 continues on page 10. * 0000800000010 * DFD 10 (b) A dialysis membrane, similar to dialysis tubing, is used in the treatment of kidney disease. During this treatment, the blood of a person with kidney disease is passed through a dialysis machine to remove unwanted waste products from the blood. The machine contains dialysate which is a solution of glucose and ions. Blood flows through the dialysis machine and is separated from the dialysate by a membrane. Some molecules diffuse from the blood into the dialysate. This is shown in Fig. 1.4. molecules diffusing into the dialysate blood from person with kidney disease dialysate (solution of glucose and ions) dialysis membrane separates the blood from the dialysate Fig. 1.4 Scientists studied the movement of two molecules, P and Q, found in the blood of a person with kidney disease. They wanted to see if these two molecules would remain in the blood or move out of the blood across the dialysis membrane into the dialysate. The scientists took samples of blood from a person using a dialysis machine every 5 minutes for 20 minutes and recorded the concentration of P and Q in these samples. The results are shown in Table 1.4. Table 1.4 time sample was taken concentration of P in the concentration of Q in the from the blood / min blood / arbitrary units blood / arbitrary units 0 200 400 5 205 280 10 200 150 15 195 90 20 200 75 * 0000800000011 * DFD 11 (i) Plot a line graph of the data in Table 1.4 on the grid in Fig. 1.5. Use a sharp pencil. Fig. 1.5 [4] * 0000800000012 * DFD 12 (ii) Calculate the percentage decrease in concentration of Q between 5 minutes and 20 minutes. Show your working and give your answer to two significant figures. …… % [2] (iii) Suggest a reason for the rate of decrease in the concentration of Q from 0 to 10 minutes and from 10 to 20 minutes. 0 to 10 minutes …… 10 to 20 minutes …… [2] [Total: 20] * 0000800000013 * DFD 13 Question 2 starts on page 14. * 0000800000014 * DFD 14

Question

K1 is a slide of a stained transverse section through a root. (a) (i) Draw a large plan diagram of the region on K1 indicated by the shaded area in Fig. 2.1. Use a sharp pencil. Use one ruled label line and the label T to identify a tissue involved in transport of substances throughout the plant. draw this region Fig. 2.1 [5] * 0000800000015 * DFD 15 (ii) Observe the cells in the centre of the root on K1. Select a group of four adjacent cells. Each cell must touch at least one of the other cells. Make a large drawing of this group of four cells. [4] * 0000800000016 * DFD 16 (b) Fig. 2.2 is a photomicrograph of a stained transverse section through the root of a different plant to K1. One difference between the section in Fig. 2.2 and the section on K1 has been labelled. Identify three other observable differences between the section in Fig. 2.2 and the section on K1. Draw three label lines on Fig. 2.2 to label the three differences you have identified. You should complete the labels to describe the differences you observe. The width of …… the cortex tissue is …… smaller in Fig. 2.2 than on K1 magnification ×35 Fig. 2.2 [4] * 0000800000017 * DFD 17 (c) A student was asked to find the area of the vascular tissue in a transverse section of root. The student grew one plant for three weeks and took a section from one of the roots. This section is shown in Fig. 2.3. A B magnification ×35 Fig. 2.3 The vascular tissue is the central region of the section. Assume that the vascular tissue is a circle. The line A–B is the diameter of the vascular tissue. (i) Calculate the actual area of the vascular tissue. Use the formula: area = πr2, where π = 3.14. actual area of the vascular tissue = …… mm2 [4] * 0000800000018 * DFD 18 (ii) The student wrote a hypothesis which stated that: The area of vascular tissue in a root section changes as the plant grows. Suggest modifications to the method used in (c) to investigate this hypothesis. …… [3] [Total: 20] DFD 19 * 0000800000020 * DFD 20