2024 TJC H2 Bio P4 MS

1 [TURN OVER TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 2 BIOLOGY 9744/04 Paper 4 Practical Answers READ THESE INSTRUCTIONS FIRST Write your name, CG, Centre number, 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. This document consists of 18 printed pages and 2 blank pages. Shift Laboratory For Examiner’s Use 1 /29 2 /10 3 /16 Total /55 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 work or if you do no u s e 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 eac h question or part question.

2 Answer all questions. 1 You are provided with a solution, labelled E, containing an enzyme which coagulates (clots) milk. Calcium ions are required for this coagulation. You are required to: • carry out a trial test to think about sources of error • investigate the effect of substrate concentration on this en zyme-catalysed coagulation. When a mixture of milk, cal cium chloride solution and E is gently rotated in a boiling tube the coagulation goes through the stages shown in Fig. 1.1. Stage 4 is the end-point of the enzyme-catalysed coagulation as shown in Fig. 1.1. Fig. 1.1 You are provided with:  20% calcium chloride solution C, in a container labelled C  1% enzyme solution E, in a container labelled E  M i l k M, in a container labelled M  distilled water W, in a container labelled W. Both calcium chloride solution C and renin solution E are irrit ants. Suitable eye protection should be worn. If C or E comes into contact with your skin, wa sh off immediately under a tap. You are required to carry out a trial test (step 1 to step 16) before you start your investigation. Read step 1 to step 16 before proceeding. Proceed as follows. 1 You are provided with a beaker labelled water-bath. Use the hot and cold water to set up a water-bath in this beaker. The starting temperature of the water-bath should be between 35 °C and 40 °C. You will not need to maintain this temperature during steps 2 to 15. 2 Put 10.0 cm 3 of M into a boiling tube. 3 Repeat step 2 so that you have two boiling tubes containing M. stage 1 stage 2 stage 3 near the end point stage 4 end point film of milk flows / drains back into milk quickly film of milk drains slowly and sticks to inside of boiling tube small spots / clots stick to inside of boiling tube as film of milk drains back all the milk has coagulated

3 [TURN OVER 4 Put 1.0 cm3 of C into each boiling tube. 5 Gently shake each of the boiling tubes to mix M and C. 6 Take the temperature of the water-bath and record this temperature in (a)(ii) on page 4. 7 Put the boiling tubes into the water-bath and leave for at least 3 minutes. (a) (i) Explain why the boiling tubes are left in the water-bath for at least 3 minutes in step 7. [1] To allow contents of the test-tubes to reach the temperature of the water-bath. (@ to allow contents/solutions/mixture to equilibrate to temperature of the water bath) Reject if 1. students stated a range of temperature 2. refer to enzymes (Note: enzymes have not been added yet) 3. refer to maintaining optimum temperature 4. refer to temperature fluctuating 8 Remove one of the boiling tubes from the water-bath. The process of coagulation will start when E is added to the boiling tube. 9 Put 1.0 cm3 of E into the boiling tube, so that it runs down the side of the boiling tube and forms a layer on the surface of the mixture, as shown in Fig. 1.2. Fig. 1.2 10 Gently shake the boiling tube to mix the solutions and start timing. 11 Hold the boiling tube over a piece of black card on the table as shown in Fig. 1.3. 12 Gently rotate the boiling tube to form a film of milk on the inside of the boiling tube. boiling tube held at an angle boiling tube held at an angle

4 Fig. 1.3 13 Observe the film until the end-point is reached (stage 4 in Fig. 1.1). Ignore any small bubbles on the inside of the boiling tube. Stop timing. 14 Record in (a)(iii) the time taken to reach the end-point. If the end-point has not been reached in 3 minutes, stop the experiment and record ‘more than 180’. 15 Repeat step 8 to step 14 with the other boiling tube in the water-bath. 16 Take the temperature of the water-bath when the final boiling t ube has been removed and record this in (a)(ii). (ii) Temperature may be a source of error in this investigation. State the temperatures of the water-bath. temperature of water-bath taken in step 6: 40 °C temperature of water-bath taken in step 16: 36 °C Explain whether the temperature of the water-bath is a signific ant source of error in this investigation. [1] Temperature of water-bath is a significant source of error because the temperature dropped from 40oC to 36oC when the final tube was removed. Note: the reason for recording the temperature in step 6 and in step 16 is to alert student to fact that the temp was not maintained. (iii) Record your results in an appropriate table. [3] Solution Time taken to reach end-point / s M Reading 1 Readin g 2 Average 19 23 21 CH: Column heading with UNITS – 1 mark D : Records 2 readings – 1 mark Pr : data recorded whole number for second – 1 mark (iv) A significant source of error for this investigation is decidin g when the end-point is reached. Suggest one advantage of carrying out this trial test before investigating the effect of substrate concentration on this enzyme-catalysed reaction. [1]  To learn how to identify when the end-point reached

5 [TURN OVER (v) Complete Table 1.1 by stating:  t w o other possible sources of error that may have affected your results  an improvement to reduce the effect of each error. Table 1.1 error improvement 1. The reaction was not carried out at a constant temperature. which can affect rate of coagulation. Keep boiling tube in water-bath while observing clotting. 2. Solution E /Enzyme solution is not equilibrated to same temperature before adding to mixture. which can affect rate of coagulation. Prepare 5.0 ml of solution E into a clean test tube and place it in the same water-bath. 3. Rate of rotation is not standardized, which can affect rate of coagulation. Use a rotating machine / magnetic stirrer/ shaker to standardize the rotation rate. 4. Some solution E / enzyme is stuck at the side of the boiling tube (did not flow down into the mixture), resulting in differences in the volume of E used in each set-up.  Add solution E to the mixture directly. Or  Use a longer syringe to release solution E at the side of the boiling tube nearer to the mixture / deeper into the boiling tube . [4] vi) You are required to make up a final volume of 10.0 cm3 of five different concentrations of calcium chloride solution by proportional dilution = simple dilution. These must include 20% calcium chloride and 0% calcium chloride solutions. Show, in a table, how you will make up the calcium chloride sol ution using the 20% calcium chloride solution, C, and distilled water, W. [3] concentration of calcium chloride solution / % volume of calcium chloride solution / cm3 volume of distilled water/ cm3 20 10.0 0.0 15 7.5 2.5 10 5.0 5.0 5