2026 DHS H2 Prelim Paper 4 answers with marker's comments

© DHS 2026 9477/04 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 BIOLOGY Paper 4 Practical You must answer on the question paper. 9477/04 1 September 2026 2 hours 30 minutes You will need: The materials and apparatus listed in the confidential instructions. INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. ● Write your name, centre number/index number and class in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen. Do not use correction fluid or tape. ● Do not write on any bar codes. ● You may use an approved calculator. ● Write the details of the shift and laboratory in the boxes provided. INFORMATION ● The total mark for this paper is 50. ● The number of marks for each question or part question is shown in brackets [ ]. Shift Laboratory For Examiner’s Use 1 20 2 18 3 12 Total 50 This document has 20 pages. Any blank pages are indicated.

2 © DHS 2026 9477/04 [Turn over Suggested Answers QUESTION 1 Plant extract has both starch and ascorbic acid. A scientist would like to investigate how the result of starch test is affected by the presence of ascorbic acid. You are required to: • set up a Visking tubing containing plant extract, P, which contains ascorbic acid, as shown in Fig. 1.1. • investigate the diffusion of ascorbic acid from P into water surrounding the Visking tubing, V, over a period of 15 minutes. • decide the level of distilled water, W, to put into the beaker • remove samples of the water surrounding the Visking tubing at 5-minute intervals for 15 minutes, starting at 0 minute. Fig. 1.1 Samples of water surrounding the Visking tubing will be removed for testing in a test-tube, so you need to take this into account when you decide the level of water to put into the beaker. (a) (i) Draw on Fig. 1.1 the level of the water • before you remove any samples (label ‘before’), • after the total volume of water needed for all the tests has been removed (label ‘after’). two levels drawn labelled with ‘before’ + ‘after’ + water level after lower than before [1] lowest level still covers contents of Visking tubing [1] [2] ‘before’ ‘after’ • water level must still cover contents of Visking tubing; • water level must be lower than ‘before’;

3 © DHS 2026 9477/04 [Turn over To compare the concentration of ascorbic acid in the samples, you are required to find the volume of iodine solution, I. You will need to add drops of I until a blue colour appears, as shown in Fig. 1.2. When this blue colour lasts for more than 5 seconds, this indicates the endpoint and the volume of I that has been added should be recorded. Fig. 1.2 (ii) In order to compare the ascorbic acid concentrations, state one variable which you will need to standardise when finding the volume of I added to each sample. Describe how you will standardise this variable. variable: volume of (ascorbic acid / W) / starch [Reject: volume of water to be removed] description: use a 3-cm3 syringe (Accept: appropriate capacity) to draw 3 cm3 of ascorbic acid / 1 cm3 of starch; Marker’s comments: [Scope] Some students did not mention the apparatus to be used and/or did not mention the exact volume to be used. [Misconception] Some students talked about standardising the size of the drop of iodine solution to be added by using the same syringe, but this is not an acceptable answer as 1) it cannot be controlled, and 2) the differences in the size of the drop is insignificant and the resultant volume of iodine solution used is more important rather than counting number of drops. [2]

4 © DHS 2026 9477/04 [Turn over Proceed as follows: 1. Put 1 cm3 of starch, S into the four test -tubes you will require in order to test the samples of water. 2. Tie a knot in the Visking tubing as close as possible to one end so that it seals the end. 3. To open the other end, wet the Visking tubing and rub the tubing gently between your fingers. 4. Put 6 cm3 of P into the open end of the Visking tubing. 5. Rinse the outside of the Visking tubing by dipping it into the water in the container labelled V. 6. Put the Visking tubing into an empty beaker as shown in Fig. 1.1. 7. Make sure the open end of the Visking tubing is held in place by a paperclip. You will start timing as soon as you add distilled water, W (steps 8 and 9). You should read steps 8 to 17 before proceeding. 8. Put W into the beaker to the level you decided in (iii). 9. Immediately start timing and remove 3 cm3 of first sample of water and put into a prepared test- tube (as in step 1). 10. Test the sample (as in steps 11 to 17). 11. Shake the test-tube gently to mix the contents. 12. Fill a 1 cm3 syringe with 1 cm3 of I. 13. Wipe off any drops of I from the outside of the syringe with a paper towel. 14. Add one drop of I to the mixture in the test-tube as shown in Fig. 1.2. 15. Mix gently and if there is no colour change add another drop. 16. Continue adding drops, one at a time, until the blue colour appears. Wait 5 seconds to see if the endpoint has been reached. If the blue colour disappears then add another drop. 17. Repeat step 16 until the mixture stays blue for at least 5 seconds. (iii) Record the volume of I needed to reach the endpoint. volume: 0.05 cm3 (Accept: 0.05 cm3 – 0.20 cm3) [Reject: No units] [number should be same as table] Marker’s comments: [Misconception] Some students gave the wrong precision, such as 1 d.p. or 3 d.p.. In this case here, a 1 cm 3 syringe was used, so the precision should be 2 d.p.. Do not simply ‘memorise’ common decimal places or inflate them – you have to see the instrument used in the experiment. [1]

5 © DHS 2026 9477/04 [Turn over 18. After 5 minutes, gently mix the water surrounding the Visking tubing and then remove the next sample, put it into a different (prepared) test-tube and repeat steps 11 to 17. 19. Repeat step 18 for 10-minute and 15-minute samples. Record your results in (a)(iv) here. (iv) Record your results in the space below. Time / min Volume of iodine / cm3 0 0.05 5 0.25 10 0.30 15 0.40 1 Correct heading with units ; 2 Records results at four timings (0, 5, 10, 15) ; 3 Increasing trend of volume of iodine ; 4 Volume to 2d.p. + Time in whole number ; [4] Marker’s comment: Independent variable must be in the first column. This is a result table; other data e.g. prep volume, final/initial volume, number of drops, should not be in this table. The time here is set as independent variable, it is not measured, so it does not need decimal places for precision. (v) Using result in (iv), describe and explain the relationship between the volume of iodine added and the amount of ascorbic acid in the sample. [quote data from iv] As time increased from 0 to 15 min, volume of iodine added increased from 0.05 cm3 to 0.04 cm3; [explain] this is because, as time increased, more ascorbic acid moves from Visking Tubing into W; [explain] In the presence of increasing ascorbic acid concentration, you would need more iodine to test for the same volume of starch;

6 © DHS 2026 9477/04 [Turn over [3] Marker’s comment: Many students did not “use result in (iv)” and so missed the data mark. Some students try to explain the chemical reaction between ascorbic acid and iodine. BUT there is no past knowledge for you to make reference