2022 HCI JC2 H2 Biology Prelims Paper 4 QP

© Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 HWA CHONG INSTITUTION JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 21S7 __ CENTRE NUMBER INDEX NUMBER BIOLOGY Paper 4 Practical No additional materials are required. 9744/04 31 August 2022 2 hours 30 minutes INSTRUCTIONS TO CANDIDATES There are three questions to this paper. Write your name, CT group, Centre number and index number in the spaces provided at the top of this cover page. 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 17 printed pages. Shift Laboratory For Examiners' Use 1 / 20 2 / 15 3 / 20 Total / 55

2 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 QUESTION 1 Cheese-making is a process that concentrates protein, fat and other nutrients from milk. This process involves coagulating the casein protein in milk. Coagulation of milk occurs when the protein and lipid molecules in milk aggregate together forming a solid substance that is separated from the liquid component. Coagulation of milk can be caused by acidification of milk, the action of an enzyme (such as rennin), or a combination of the two. It has been found that t he usage of fruit extracts as a commercially- produced milk coagulant can increase the flavour and texture of the final cheese. You are required to:  make and record observations on the coagulation of milk by acid and rennin,  investigate the relative effective ness of acid and rennin in milk coagulation by measuring the time taken for milk coagulation to occur,  determine whether a fruit extract that is often used to make commercial coagulants contain acids, rennin, or both, as its active ingredient. You are provided with:  one slice of pineapple P, in a plastic bag,  diluted hydrochloric acid solution, in a container labelled H,  diluted rennin enzyme, in a container labelled E,  milk, in a container labelled M. Diluted hydrochloric acid H is corrosive. Suitable eye protection and gloves should be worn. If H comes into contact with your skin, wash off immediately under tap water. Care should be taken when using hot water. Proceed as follows. The coagulation of M by H can be observed using the following steps: 1 Add 5.0 cm3 of M to a test-tube. 2 Add 1.0 cm3 of H to the M in the same test-tube. Gently push the plunger of the syringe so that H runs slowly down the side of the test-tube to the bottom. This is shown in Fig. 1.1 (a).

3 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 Fig. 1.1(a) 3 Tilt the tube and rotate it slowly as shown in Fig. 1.1(b). Do not shake the tube. Fig. 1.1 (b) (a) (i) Record your observations of the sides of the test-tube. [1] 4 Repeat the procedure in steps 1 to 3, using a new sample of M, clean glass apparatus and E instead of H to observe the coagulation of M. (a)(ii) State how your observations from addition of E differ from your answer in (a)(i). [1] Milk and H push gently syringe test-tube H running slowly down the side of the test-tube test-tube held at an angle M and H rotate test-tube slowly

4 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 (a)(iii) Based on your observations in (ii), state whether H or E is more effective as a milk coagulant. [1] (iv) Confidence in the results of this investigation may be limited by lack of replication and sources of error. Describe two other significant sources of error in this procedure. [2] (a)(v) Suggest how you could make two improvements to the procedure so that a more accurate estimate of the relative effectiveness on coagulation could be obtained. [2] (b) In some commercially produced milk coagulant s, fruit extracts are used. Pineapple contains numerous enzymes as well as acid that could act as coagulants. A student wished to investigate the relative effectiveness of using pineapple extract , PE, to coagulate milk, as compared to H and E. 5 Cut the piece of pineapple P into smaller pieces on a white tile. 6 Use the mortar and pestle to crush and grind the pineapple pieces to obtain a mash. 7 Label a large plastic vial ‘PE’. 8 Filter the mash through the sieve into the large plastic vial labelled PE. Discard the soiled gloves. You may use a new pair when answering Question 2. While you are collecting filtrate PE, continue to read through this Question Paper up to step 9 and complete (b)(ii).

5 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 (a)(i) Use the information provided to plan a method that you can use to determine if PE coagulates milk by its acidity or by the presence of coagulating enzymes such as rennin. The time taken for coagulation can be recorded, up to a maximum of 120 seconds. You will carry out this method in step 9. You do not need to:  plan to carry out repeats and replicates  include details of how to test the samples for coagulation  include details of how the pineapple extract can be obtained. In your plan, you must use:  milk, M  pineapple extract, PE  thermometer and boiling water bath. You may select from any of the other apparatus and materials provided. Your plan should:  have a clear and helpful structure such that the method you use is able to be repeated by anyone reading it  include details to ensure that the results are as accurate and repeatable as possible  use the correct technical and scientific terms  only make use of the apparatus and materials provided.

6 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 [5] Before proceeding further, use the container labelled hot water to collect approximately 400 cm3 of hot water from where it is provided in the laboratory. The container labelled tap water can be filled as necessary from the tap. 9 Carry out your method described in (b)(i) to determine if the coagulative properties of pineapple is due to acidity, enzyme or both. (a)(ii) Use the space provided to record your results in a suitable format. [3]

7 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 (a)(iii) Based on your results, state and explain whether the coagulative properties of pineapple is due to acidity, enzymes or both. [4] (a)(iv) State an assumption that needs to be made in order for your results to be valid. [1] [Total: 20]

8 © Hwa Chong Institution 2022 9744 H2 Biology / JC2 Preliminary Examinations / Paper 4 QUESTION 2 Another way to make cheese is through the use of a starter culture containing bacteria and yeast, mixed with a substrate. Different substrates can be used, such as glucose and maltose. The chemical tetrazolium chloride (TTC) can be used in investigating the