2023 ASRJC JC2 H2 Biology Prelims Paper 4 (ANS)

ASRJC BIOLOGY DEPT 9744/2023/J2PRELIM/P4 [Turn over H2 ANDERSON SERANGOON JUNIOR COLLEGE HIGHER 2 2023 JC2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS INDEX NUMBER BIOLOGY 9744/04 Paper 4 Practical 30 August 2023 Wednesday 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. READ THESE INSTRUCTIONS FIRST Write your name, class and index number 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, glue or correction fluid. 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. 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. This document consists of 15 printed pages and 1 blank page. Shift Laboratory For Examiner’s Use 1 2 3 Total /55

1 ASRJC BIOLOGY DEPT 9744/2023/J2PRELIM/P4 Answer all questions. 1 Plant cells con tain en zymes that catalyse metabolic reactions. Some of these enzymes catalyse the release of oxygen from hydrogen peroxide. A plant extract solution can be produced which will contain these enzymes. When hydrogen peroxide and a plant extract solution are mixed, oxygen is released. The oxygen forms bubbles that make a foam on the surface. You are required to investigat e the effect of pH on the progress of the enzyme-catalysed reactions by: • changing the pH using buffers • measuring the height of the foam produced by the release of oxygen. To follow the progre ss of this reaction, you will nee d to measure the height of foam at different times for a total of 3 minutes. (a) (i) Decide how often you will take these measurements , including the final height of foam at 3 minutes. State the times when you will measure the height of foam. [1] Must state at least 5 timings to measure, at regular intervals → preferred: 30s, 60s, 90s, 120s, 150s, 180s [must] (ii) Fig. 1.1A shows how a test-tube will be set up at the start (0 minutes). Fig. 1.1B shows the test-tube after 3 minutes. Fig. 1.1 The top of the foam may not form an even layer, so you will need to decide where to measure the layer of the foam. Draw a double-headed arrow on Fig. 1.1B to show where you will measure this layer of foam. [1] 1. top and bottom of arrow to appropriate height;

2 ASRJC BIOLOGY DEPT 9744/2023/J2PRELIM/P4 You are provided with: labelled contents volume / cm3 E plant extract solution 40 H hydrogen peroxide solution 70 B4 buffer pH4 10 B5 buffer pH5 10 B7 buffer pH7 10 B9 buffer pH9 10 B10 buffer pH10 10 U unknown buffer 10 D liquid detergent 10 If any of these liquids come into contact wit h your skin, wash off im mediately un der cold water. It is recommended that you wear suitable eye protection. Temperature affects the rate of an enzyme -catalysed reaction and ma y be a significant source of error. You are required to measure the temp erature of the room befo re the start of the investigation and when all the measurements have been recorded. Proceed as follows: Read step 1 to step 9. 1. Measure the temperature of the room and record this measurement in (b)(iii) on page 6. 2. Put 1 cm3 of buffers B4, B5, B7, B9, B10 into separate test-tubes. 3. Put 2 cm3 of E into each test-tube. Gently shake to mix well. 4. Put 1 drop of D into each test-tube. Do not mix. The reaction will start as soon as H is added to the mixture of E and buffer. 5. Put 5 cm3 of H into one of the test-tubes. 6. Immediately start timing. 7. Using the str ip of gr aph paper pr ovided, measure the height of the foam as decided in (a)(ii), at each of your sampling times as stated in (a)(i), until you have recorded the final measurement at 3 minutes. Record your measurements in (b)(i). If the foam flows over the top of the test-tube, stop timing. Record the measurement of the height of the foam to the top of the test -tube and add an asterisk (*) to show that the foam has flowed over. 8. Repeat step 5 to step 7 with each of the other buffer solutions.

3 ASRJC BIOLOGY DEPT 9744/2023/J2PRELIM/P4 9. Measure the temperature of the room now that all the measurements have been recorded. Record the temperature in (b)(iii). (b) (i) Record your results for the height of foam in an appropriate table below. [4] pH Height of foam at specific time interval / mm 30s 60s 90s 120s 150s 180s 4 0 0 2 3 3 3 5 2 2 3 3 4 4 7 4 6 6 6 8 8 9 4 4 5 5 5 6 10 3 4 4 4 4 4 1. table drawn and correct headings: pH and height of foam/mm ; 2. records results for 5 pH values and all time intervals stated in (a)(i); 3. height of foam recorded as whole mm ; 4. correct trend → maximum height of foam at 180s at pH 7 ; (ii) Using your raw results for pH 5: • State the highest height of foam ........................ mm. • State the first time when this height was reached ........................ seconds. Using these measurem ents, calculate the rate of production of oxygen, as millimetres per second (mm s-1). Show your working. 1. shows maximum height of foam for pH 5 divided by time ; 2. answer to the appropriate degree of accuracy (to 2 or 3 sf) ; rate of oxygen production = ................................................... mm s–1 [2] (iii) State the temperature of the room before the start of the investigation. ........................ °C State the temperature of the room after all the measurements have been recorded. ........................ °C State the difference between this temperature and the temperature of the room at the start of the investigation. difference = ......................... °C Explain whether temperature is a significant source of error in this investigation. [1] unlikely a significant source of error because did not differ significantly/ temperature was the same throughout (and independent and dependent variable was not temperature) + correct recording of temperature to 1 d.p.

4 ASRJC BIOLOGY DEPT 9744/2023/J2PRELIM/P4 You are now required to estimate the pH of the buffer in U using the same procedure. 10. Put 1 cm3 of U into a test-tube and repeat step 3 to step. Record your results in (b)(iv). (iv) Record the maximum height of foam using U. 1. states the height of foam for U in mm, to whole number; .......................... mm [1] (v) Using the result in (b)(iv) and the results in (b)(i), estimate the pH of U. 1. estimates the correct pH using the result stated in (b)(iv) , in comparison w ith maximum heights of foam for each buffer of know n pH after 3 minutes in results table in (b)(i) (U is actually pH 5 → accept range between 4 to 7) pH ...................................... [1] (vi) This procedure investigated the effect of pH on the activity o f the enzymes in a plant extract solution. To modify this procedure for investigating the effect of substrate concentration on the activity of enzymes in