2025 EJC JC2 Prelim 9744 Biology P4 (A)

© EJC 2025 9744/04/J2H2PRELIM/2025 EUNOIA JUNIOR COLLEGE JC2 Preliminary Examinations 2025 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME ANSWERS CIVICS GROUP 2 4 - REGISTRATION NUMBER BIOLOGY Paper 4 Practical 9744/04 26 August 2025 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration 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 stapler, paper clips, highlighters, glue or correction fluid/tape. This document consists of 17 printed pages. For Examiner’s Use 1 2 3 Total 55 Answer all questions in the spaces provided in 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. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory

2 © EJC 2025 9744/04/J2H2PRELIM/2025 1 The enzyme amylase catalyses the hydrolysis (breakdown) of starch to reducing sugars, as shown in Fig. 1.1. Fig. 1.1 A student investigated the effect of temperature on the hydrolysis of starch by the enzyme amylase, which has an optimal temperature close to 40°C. The student carried out the following steps: • step 1: put 2 cm 3 of amylase into a test-tube • step 2: put 18 cm3 of starch solution into a different test-tube • step 3: put the test-tubes into a water-bath at 10°C • step 4: left the test-tubes for 3 minutes • step 5: put the starch solution into the test-tube containing the amylase • step 6: left the test-tube for 2 minutes • step 7: immediately determined the relative amount of reducing sugars in the test-tube • repeated steps 1 to 7 at 40°C and at 100°C. You are provided with three beakers, S1, S2 and S3. These three beakers contain the same products of the reaction involving starch and amylase as the test-tubes prepared by the student in step 6. Each beaker contains the products of the reaction produced at one of the three temperatures tested. You will determine: • the relative amount of reducing sugar present in each beaker • the presence or absence of starch in each beaker • which of the beakers S1 , S2 and S3 contain products of the amylase -catalysed reaction carried out at 10°C, 40°C and 100°C respectively. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 S1 products of the reaction between starch and amylase carried out at a particular temperature none 20 S2 products of the reaction between starch and amylase carried out at a particular temperature none 20 S3 products of the reaction between starch and amylase carried out at a particular temperature none 20 U products of the reaction between starch and amylase at an unknown temperature none 20 B Benedict’s solution irritant 30 iodine iodine solution irritant 15 If any solution comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection.

3 © EJC 2025 9744/04/J2H2PRELIM/2025 [Turn over To investigate the effect of temperature on the hydrolysis of starch by the enzyme amylase you will need to: • carry out the test for reducing sugars on S1, S2 and S3 • determine the relative amount of reducing sugar in each solution • carry out the test for starch on S1, S2, and S3 • determine the presence or absence of starch in each solution. (a) (i) Explain why the student left the test -tubes in the water bath for 3 minutes before adding the starch solution. [1] To allow for equilibration, whereby contents of the test-tubes reach the temperature of the water bath. To determine the relative amount of reducing sugar in each solution, the time to the first colour change will be measured using 5 cm3 of each solution. (ii) Describe how you will carry out the test for reducing sugars. [1] Add same volume / 5 cm3 of Benedict’s solution with solution to be tested, and heat in boiling water bath for 5 minutes. (iii) State how you will determine which solution has the highest amount of reducing sugar present. [1] Solution with the highest amount of reducing sugar will have the shortest time for first colour change. (iv) State the independent variable in this investigation. [1] temperature Carry out step 1 to step 5. step 1 Label one test-tube, S1. step 2 Put 5 cm3 of S1 into the test-tube. step 3 Repeat step 1 and step 2 for S2 and S3. step 4 Carry out the test for reducing sugars as you described in (a)(ii). If the time taken to the first colour change is longer than 120 seconds then record as ‘more than 120’. step 5 Record in (a)(v) the time taken to the first colour change for each solution. Carry out step 6 to step 11 to test for the presence of starch. step 6 Label a clean test-tube, S1. step 7 Put 5 cm3 of S1 into the test-tube. step 8 Repeat step 6 and step 7 for S2 and S3. step 9 Put 2 drops of iodine solution into each test-tube. Shake gently to mix. If any starch is present the solution will change to a blue-black colour. step 10 Observe the colour in each test-tube. step 11 Record in (a)(v) the colour for each solution.

4 © EJC 2025 9744/04/J2H2PRELIM/2025 (v) Record your results in an appropriate table. [4] Solution Time taken for first colour change for reducing sugar test / s Colour observed for starch test S1 S2 S3 1. Heading with appropriate units (time taken for first colour change for reducing sugar test / s, colour observed for starch test) R: units in body of table 2. Correct trend for results of reducing sugar test - Time taken: S3 < S1 < S2 - S2 needs to be recorded as “more than 120” (R: > 120) 3. Precision of timing: to whole number in seconds 4. Colour correctly described for each sample for starch test; negative test: yellow-brown / brown (S3) (R: orange) positive test: blue-black (S1 and S2) Note: S1 = 0.5% starch and 1% glucose S2 = 1% starch S3 = 10% glucose (vi) Complete Table 1.2 using your results in (a)(v). For reducing sugar content use only the words: none, low, medium or high. For presence of starch use only the words: present or absent. You may use each word once, more than once or not at all. Table 1.2 reducing sugar content presence of starch S1 low / medium present S2 none present S3 high absent 1. correct trend for reducing sugar based on candidate’s results; 2. correct results for starch based on candidate’s results; [2]

5 © EJC 2025 9744/04/J2H2PRELIM/2025 [Turn over (vii) Explain which of the beakers S1, S2 and S3 contain products of the amylase - catalysed reaction carried out at 100°C. [3] 1. S2 contained products of the amylase-catalysed reaction carried out at 100°C; 2. First colour change was not observed for S2 (A: S2 did not show colour change) for the reducing sugar test. This showed that none of the starch was hydrolysed to form reducing sugars. OR Presence of starch and absence of reducing sugar showed that starch was not hydrolysed to form reducing sugars. 3. This is because at 100°C, amylase was denatured and did not hydrolyse starch; U contains the products of the reaction involving starch and amylase solution in a water -bath at an unknown temperature. You will need to: • carry out the test for reducing sugars and the test for starch on U • compare the results for U with the results for S1, S2 and S3