HCI 2024 Prelim H2 Bio P4 Qn

© Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 HWA CHONG INSTITUTION JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 23S7__ CENTRE NUMBER INDEX NUMBER BIOLOGY Paper 4 Practical Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. 9744/04 26 August 2024 2 hours 30 minutes INSTRUCTIONS TO CANDIDATES There are two question booklets ( I and II) to this paper. Write your name, CT group, Centre number and index number in the spaces provided at the top of this cover page and on the lines provided at the top of the cover page of Booklet II. 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. Answer all questions in the spaces provided on the question paper. INFORMATION FOR CANDIDATES 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. The number of marks is given in brackets [ ] at the end of each question or part question. You are reminded of the need for good English and clear presentation in your answers. This document consists of 16 printed pages. Shift Laboratory For Examiners' Use 1 / 30 2 / 25 Total / 55

2 © Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 QUESTION 1 A group of students investigated the growth of different varieties of yeast. The students learnt that the rate of respiration can be used as a measure of the growth of a yeast culture, which depends on a variety of factors. One such factor is the activity of enzymes that are responsible for hydrolysing sucrose into reducing sugars to be used as respiratory substrate. You will investigate the activity of the enzymes in yeast cells, which will be immobili sed in sodium alginate beads. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 Y yeast cell suspension none 40 A sodium alginate solution harmful irritant 20 C calcium chloride solution harmful irritant 30 S sucrose solution none 100 B Benedict’s solution harmful irritant 30 If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. You will investigate the activity of yeast enzymes by using different numbers of beads of immobilised yeast cells in sucrose solution, S. Carry out steps 1 – 9 to immobilise the yeast cells in sodium alginate beads. 1 Put 10 cm3 of A into a beaker. 2 Stir the yeast cell suspension Y with a glass rod. 3 Put 10 cm3 of Y into the beaker containing A and mix well. Do not introduce bubbles into the mixture. 4 Put 20 cm3 of C into another beaker. 5 Use a 10 cm3 syringe to collect 10 cm3 of the mixture of A and Y.

3 © Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 6 Hold this syringe over the beaker containing 20 cm3 of C (step 4), as shown in Fig. 1.1. Fig. 1.1 7 Hold the barrel of the syringe with one hand while slowly pressing down on the plunger with the other hand so that a drop of the mixture is released into solution C. The drop will form a bead. 8 Repeat step 7 to make at least 31 beads. The immobilised yeast beads must be left in the beaker for 5 minutes. 9 After 5 minutes tip the beads and the solution into a Petri dish. You will test the activity of the yeast enzymes by using different numbers of beads (1, 2, 4, 8 and 16) in sucrose solution. Carry out steps 10 – 20. 10 Label five beakers 1, 2, 4, 8 and 16 and label five test-tubes 1, 2, 4, 8 and 16. 11 Put 1, 2, 4, 8 or 16 beads into each of the appropriately labelled beakers, as shown in Fig. 1.2. Fig. 1.2 slowly press down to release one drop at a time mixture of A and Y calcium chloride solution, C plunger barrel of syringe one drop released yeast bead 1 2 4 8 16

4 © Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 12 Put 10 cm3 of sucrose solution, S, into each of the beakers containing the beads. 13 Start timing and leave for 5 minutes. While you are waiting set up a water-bath ready for step 14 and step 19. In step 19 you will use the water -bath to carry out the test for reducing sugars using Benedict’s solution, B. 14 Heat the water-bath to around 90 °C to 100 °C. 15 At the end of 5 minutes (step 13) stir the contents of each beaker. 16 Use a syringe to transfer 2 cm3 of the solution from beaker 1 into the test-tube labelled 1. 17 Repeat step 16 for each of the beakers and test-tubes labelled 2, 4, 8 and 16. 18 Put 2 cm3 of Benedict’s solution, B, into each of the test-tubes labelled 1, 2, 4, 8 and 16. 19 Put test-tube 1 into the water-bath and time how long before the appearance of the first colour change. If there is no colour change after 2 minutes, stop timing and record as ‘more than 120’. Record your result in (a)(ii). 20 Repeat step 19 for the other test-tubes, 2, 4, 8 and 16. (a)(i) State the independent variable in this investigation. [1] (a)(ii) Record your results in an appropriate table. [4]

5 © Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 (a)(iii) Explain your results in (a)(ii). [2] (a)(iv) Other than lack of replicates and repeats , identify one main source of error in this investigation and suggest an improvement to reduce the effect of this error. source of error: improvement: [2] (a)(v) A student set up a beaker as a control experiment. The result of the control experiment showed that the sucrose was hydrolysed by an enzyme. Suggest what substances the student put in the beaker for the control experiment. [1] (a)(vi) The procedure described in step 1 to step 20 investigated the effect of changing the number of yeast beads on the rate of hydrolysis of sucrose. Describe how you would modify the procedure to investigate the effect of changing the concentration of the sucrose solution on the rate of hydrolysis of sucrose. [2]

6 © Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 Another factor which could affect the rate of respiration is the variety of yeast. Respiration rates can be measured using the redox indicator TTC. • During respiration, hydrogen ions are removed from reducing sugars to reduce hydrogen carriers such as NAD and FAD. • A redox indicator can be used as a hydrogen carrier in experimental conditions instead of NAD or FAD. • The colour change of the redox indicator can be measured using a colorimeter. Carry out a preliminary experiment to determine how the colour change of TTC would be like. Using a 10 cm 3 syringe, add 5 cm 3 of yeast cell suspension Y into a conical flask, followed by 10 cm3 of sucrose solution, S and 1 cm3 of TTC, T as shown in Fig. 1.3. Observe the colour of TTC. Fig. 1.3 (b)(i) Record the colour change of TTC after 10 minutes. [1] (b)(ii) Explain why the colour change of TTC in (b)(i) can only be observed after 10 minutes and not immediately upon addition. [2] yeast suspension Y mixed with sucrose solution S and T

7 © Hwa Chong Institution 2024 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 (c) Three different varieties of yeast, commonly used in food manufacture, are compressed yeast, active dry yeast and instant yeast.