NYJC 2023 J2 Prelim Paper 4 Qn (For Sharing)

9744 / H2 Biology / 04 NANYANG JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME CLASS BIOLOGY 9744/04 Paper 4 Practical 24 August 2023 Candidates answer on the Question Paper Additional Materials: As listed in the Confidential Instructions 2 hour 30 minutes READ THESE INSTRUCTIONS FIRST Write your name and CT on all the work you hand in. Give details of the practical shift and laboratory, where appropriate in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Shift Laboratory At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 Total This document consists of 20 printed pages and 0 blank page. [Turn over

9744 / H2 Biology / 04 2 Answer all the questions. 1 Some fruit contains large quantities of ascorbic acid (vitamin C). Ascorbic acid can be absorbed through the partially permeable wall of the gut. You will investigate the rate at which ascorbic acid from a 2 gdm–3 ascorbic acid solution diffuses across a partially permeable membrane. Dialysis (Visking) tubing acts as a partially permeable membrane. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard quantity A 2 gdm-3 ascorbic acid solution irritant 80cm3 W distilled water none 200cm3 D dialysis tubing in distilled water none 20cm I iodine solution irritant 25cm3 S starch solution none 20cm3 It is recommended that you wear suitable eye protection. You will need to: • allow ascorbic acid to diffuse out of the dialysis tubing into the distilled water surrounding the dialysis tubing • estimate the concentration of ascorbic acid that has diffused out of the dialysis tubing. Carry out step 1 to step 27. step 1 Tie a knot in the dialysis tubing as close as possible to one end, so that the end is sealed. step 2 To open the other end, wet the dialysis tubing and rub the tubing gently between your fingers and thumb. step 3 Put 10 cm 3 of ascorbic acid solution A into the open end of the dialysis tubing. step 4 Rinse the outside of the dialysis tubing by dipping it in the container of water labelled D. step 5 Carefully place the filled dialysis tubing bag into the large test-tube and secure position using an elastic band, as shown in Fig. 1.1.

9744 / H2 Biology / 04 3 Fig. 1.1 You will need to fill the large test -tube with a known volume of distilled water so that it just covers the liquid in the dialysis tubing. step 6 Use a syringe to add the distilled water to the large test-tube and record in (a)(i) the volume you added. (a) (i) State the volume of distilled water you added. volume of water ……………………………. cm3 [1] step 7 Start timing and leave the dialysis tubing bag in the distilled water for at least 20 minutes. While you are waiting continue with this question. You will need to dilute the 2 gdm –3 ascorbic acid solution, A, to provide a range of known concentrations. You will need to make up 20 cm3 of each concentration of ascorbic acid. Table 1.2 shows how to make up two of the concentrations you should use.

9744 / H2 Biology / 04 4 (ii) Decide which other concentrations of ascorbic acid to make and complete Table 1.2. Table 1.2 concentration of ascorbic acid / gdm-3 volume of ascorbic acid solution / cm3 volume of distilled water / cm3 0.0 0.0 20.0 2.0 20.0 0.0 [3] step 8 Using the beakers provided, make up the concentrations of ascorbic acid stated in Table 1.2. step 9 Put 1 cm3 of starch solution S into a clean test-tube. step 10 Put 5 cm3 of the 0 gdm –3 ascorbic acid solution (distilled water) into the same test tube. Shake gently to mix. step 11 Fill a syringe with 2 cm3 iodine solution I. step 12 Add one drop of I to the mixture of S and ascorbic acid solution, as shown in Fig. 1.2. Mix gently. Fig. 1.2

9744 / H2 Biology / 04 5 step 13 You should see a blue colour. This is the end-point you are looking for when you test the remaining ascorbic acid solutions (step 21). step 14 Record the volume of iodine solution you have added. step 15 Put 1 cm3 of starch solution S into a clean test-tube. step 16 Put 5 cm3 of the lowest concentration of the remaining ascorbic acid solutions into the same test-tube. Shake gently to mix. step 17 Fill the syringe containing iodine solution I to the 2 cm3 level again. step 18 Add one drop of I to the mixture of S and ascorbic acid solution as shown in Fig. 1.2. Mix well. step 19 Continue adding drops one at a time, mixing after each drop, until you see a blue colour. step 20 As soon as you see a blue colour, wait 10 seconds. If the blue colour disappears then add another drop. step 21 Continue adding drops until the mixture stays blue for at least 10 seconds. This is the end-point. step 22 Record the volume of iodine solution you have added. step 23 Repeat step 15 to step 22 with the other concentrations of ascorbic acid you prepared in step 8. Record your results in (a)(iii). (iii) Record your results in an appropriate table. [5]

9744 / H2 Biology / 04 6 step 24 Remove the dialysis tubing from the large test-tube and place it in the beaker labelled For waste. Stop timing and record the time that the dialysis tubing has been left in the distilled water (time from step 7 to step 24). time = ……………………………………… step 25 Pour the solution from the large test-tube into a small beaker. step 26 Use a syringe to remove a 5 cm3 sample of the solution from the small beaker. step 27 Repeat step 15 to step 22 using this sample. Record your result in (a)(iv). (iv) Record the volume of iodine added. ………………………………… (v) Complete Fig. 1.3 to show the positions of each of the concentrations of ascorbic acid, recorded in (a)(iii). Fig. 1.3 [1] (vi) Use your results in (a)(iii) and (a)(iv) to estimate the concentration of ascorbic acid in the solution outside the dialysis tubing bag. Show this estimate on Fig. 1.3 by placing the letter U in the correct position along the line. [1]

9744 / H2 Biology / 04 7 (vii) Calculate the rate of diffusion of ascorbic acid out of the dialysis tubing. Show your working. rate of diffusion = ……………………………………… [2] (viii) Identify two significant sources of error when finding the concentration of ascorbic acid in the sample from the large test-tube. [2] (ix) Explain two improvements to the investigation that would increase confidence in the estimation of ascorbic acid in the sample outside the dialysis tubing bag. [4]

9744 / H2 Biology / 04 8 (b) Iodine solution (iodine in potassium iodide solution) turns blue- black when starch is present in plant tissues. However, as ascorbic acid is also found in plant tissues, some scientists investigated the effect of testing for starch with iodine solution when there was ascorbic acid present. The concentration of ascorbic acid was 0.0001 moldm −3 and the concentration of starch solution was standardised. The percentage of starch which reacted with the iod