YIJC 2023 [H2] Prelim.P4 (ANS)

@YIJC 9744/04/PE/2022 [Turn over YISHUN INNOVA JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO. H2 BIOLOGY 9744/04 30 Aug 2022 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name and class in the spaces at the top of this page. Write in dark blue or black pen only. You may use a soft pencil for any diagrams or graphs. Do not use paper clips, highlighters, 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. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory For Examiner’s Use 1 25 2 12 3 18 Total 55 This document consists of 14 printed pages and 2 blank pages.

2 @YIJC 9744/04/PE/2023 [Turn over Answer all questions 1 The enzyme amylase breaks down starch to form reducing sugars. It has been found that drinking tea affects the activity of amylase. You will investigate the effect of different concentrations of tea extract on the breakdown of starch by amylase. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume/cm3 E amylase solution harmful irritant 50 T1 100% tea extract none 20 S starch solution none 50 W distilled water none 150 iodine iodine solution irritant 20 If any solution comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection. You will need to carry out a serial dilution of the 100% tea extract, T1, to reduce the concentration by half between each successive dilution. You are required to make up a sufficient volume of each tea extract so that, once the serial dilution has been completed, there is a volume of at least 5.0cm 3 for each concentration prepared. (a) (i) Complete Table 1.2 to show you will make t he concentration of the tea extract T1, T2, T3, T4 and T5. Table 1.2 Tea extract T1 T2 T3 T4 T5 percentage concentration of tea extract 100 50 25 12.5 6.25 percentage concentration of tea extract to be diluted 100 50 25 12.5 volume of the tea extract to be diluted / cm3 5.0 5.0 5.0 5.0 volume of distilled water W / cm3 5.0 5.0 5.0 5.0 1 100, 50, 25, 12.5, 6.25 (% concentration of tea extract ) and 100, 50, 25, 12.5 (% concentration of tea extract to be diluted); 2 At least 5.0 cm3 for volume of the tea extract to be diluted ; 3 Equal volume of distilled water W added to the volume of tea extract to be diluted and precision to be kept to 1 decimal point ; Penalised only once for incorrect precision for MP2 and MP3

3 @YIJC 9744/04/PE/2023 [Turn over [3] Read steps 1 – 12. Proceeds as follows. 1 Prepare the concentrations of tea extract as shown in Table 1.2. 2 Label the test-tubes with the concentrations you prepared in step 1. 3 Put 1cm3 of each concentration of tea extract into the appropriately labelled test-tube. 4 Put 1cm3 of E into each of the labelled test-tubes. Shake gently to mix. 5 Using the beakers labelled hot water and cold water, set up and maintain a water -bath with water between 30°C and 40°C. 6 Put the test-tubes from step 4 into the water-bath. 7 Label a white tile, as shown in Fig. 1.2, with: • the times 2, 4, 6, 8 and 10 (minutes) • the percentage concentrations of tea extract you prepared in step 1. 8 Put drops of iodine solution onto the white tile as shown in Fig. 1.1. You will need one row of drops of iodine solution for each of the concentrations of tea extract you prepared in step 1. Fig. 1.1

4 @YIJC 9744/04/PE/2023 [Turn over 9 Put 2cm3 of starch solution S into each test-tube (in the water-bath). Shake gently to mix. Start timing. 10 After 2 minutes: • use a pipette to remove a sample of the solution from the test-tube labelled 100% • put 1 drop of the solution onto the spot of iodine solution labelled 2 (minutes) on the row labelled 100 (%) • put 1 drop of the next solution onto the spot of iodine solution labelled 2 (minutes) on the row labelled with your next concentration of tea extract • r epeat for the other concentrations of tea extract you prepared in step 1 , so that all of the drops of iodine solution in the 2 minute column have been used. 11 Repeat step 10 at intervals of 2 minutes until there is no blue-black colour. This is the end-point. Note: you will not see the original colour of the iodine due to the presence of the tea. If the iodine continues to turn blue-black at 10 minutes, stop sampling and record this as ‘more than 10’. 12 Record in (a)(ii) the time taken to reach the end-point. (ii) Record your results in an appropriate table. 1 heading for independent variable: percentage concentration of tea, and before heading for dependent variable and no units in body of table ; 2 heading for dependent variable: time taken to reach end-point and min (unit) and no units in body of table ; 3 readings for all samples and time for the highest concentration of tea more than for the lowest concentration of tea ; 4 results recorded in whole minutes ; Percentage concentration of tea extract Time taken to reach end-point / min 100 50 25 12.5 6.25 [4] (iii) State the trend for your results. As the percentage conc. of tea extract decreases from 100% to 6.25%,

5 @YIJC 9744/04/PE/2023 [Turn over the time taken to reach end-point decreases from … to … ; [1] (iv) Tea is a competitive inhibitor of amylase. Explain how tea can act as a competitive inhibitor of amylase. 1 inhibitor competes with the starch for the active site because (compound in) tea extract has a similar shape to starch ; 2 (compound in) tea extract tea is complementary to the active site and binds to active site to form enzyme-inhibitor complex ; 3 fewer enzyme-substrate complexes formed hence rate of starch hydrolysis is reduced ; [3] (v) The volume of the drops of iodine solution in step 8 was not standardised. Suggest one improvement to step 8. 1 use a syringe to place a fixed volume of iodine on the spotting tile ; [1] (vi) Identify two possible sources of error in step 9 and suggest improvements to reduce the effect of these errors. 1 starch solution not at same temperature as T and E ; 2 incubate reagents at 40 °C for equilibration ; OR OR 3 starch is added at different times to each of the test tube ; 4 carry out each test separately so that time taken for starch hydrolysis is fixed ; OR 5 uneven mixing of reagents results in uneven rate of hydrolysis ; 6 mix for a stated time; Either MP1, 2 OR MP3, 4, OR MP5, 6 [4]

6 @YIJC 9744/04/PE/2023 [Turn over (b) Caffeine is a chemical found in tea and many other drinks. A student investigated the concentration of caffeine in different types of drink. Table 1.2 shows the student’s raw data and processed data. Table 1.2 type of drink raw data processed data volume of one serving /cm3 mass of caffeine per serving /mg concentration of caffeine / mg cm–3 black tea (BT) 220 40 0.18 filter coffee (FC) 350 195 decaffeinated tea (DT) 220 5 0.02 cola light (CL) 330 33 0.10 espresso coffee (EC) 30 48 1.60 green tea (GT) 220 18 0.08 (i) Complete Table 1.2 by calculating the concentration of caffeine in filter coffee. Show your working. Concentration of caffeine in filtered coffee = 195 / 350 = 0.56 ; 1 working (195 / 350) 2 correct answer and precision (2 d.p.) ; [2]

7 @YIJC 9744/04/PE/2023 [Turn over