JPJC 2023 JC2 H2 Prelim P4 ANS

9744 / 04 [Turn over NAME : CLASS : JURONG PIONEER JUNIOR COLLEGE JC2 Preliminary Examination 2023 BIOLOGY Higher 2 9744/04 17 August 2023 Paper 4 Practical 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your class, index number and name 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 Shift Laboratory For Examiner’s Use 1 2 3 Total This document consists of 16 printed pages.

2 JPJC/JC2 H2 Biology/Prelims/2023 Answer all questions. 1 There are molecules on the surface of yeast cells which cause the cells to stick together. When a yeast suspension is placed in a test-tube some of the cells sink slowly to the bottom. (a) (i) Show clearly on Fig. 1.1 what you would expect the contents of the test-tube to look like after 10 minutes. You will gain marks for clear annotations. Fig. 1.1 [2] 1. Line draw level with half -way mark + more yeast drawn towards bottom of tube or another line to show a separate region ; 2. One annotation/label/description e.g. yeast cells sink ; You are required to investigate the effect of the independent variable, pH, on the sedimentation of a yeast cell suspension over a period of 10 minutes. (ii) State the time intervals you will use and what you will use the graph paper scale to measure. ............................................................................................................................... [2] 1. Uses 10 minutes + o ne/two minutes intervals ; R: if does not divide into 10 e.g. 3 minutes 2. Measures or describes measuring e.g. (use graph paper) to find height + description of what is measured e.g. from halfway mark to top of sediment or bottom of tube to top of sediment/AW ;

3 JPJC/JC2 H2 Biology/Prelims/2023 [Turn over You are provided with: • a suspension of yeast cells, Y, in a beaker labelled Y • calcium chloride solution, C, in a container labelled C • buffer pH 3, pH 4, pH 5 and pH 6 in containers labelled pH 3, pH 4, pH 5 and pH 6. Proceed as follows. 1 Label one test-tube for each pH. 2 Use the marker provided to mark a line half -way along the length of each test -tube as shown in Fig. 1.1. You will need to put 1 cm 3 of C in each test-tube, and then an equal volume of Y and each buffer solution so that the mixture will fill the test -tube to the half -way mark as shown in Fig. 1.2. Fig. 1.2 (iii) Use the test -tube labelled T and the other apparatus provided and decide on the volume of Y and the volume of each buffer solution to use. Describe all the steps you used to work out the volumes. ............................................................................................................................... [1] 1. Describes all following steps: add 1 cm 3 C + measure volume up to the half- way line + divides volume by half ; State the volume of Y and the volume of each buffer solution to use. volume of Y ........................................4.5 cm 3 (4-4.5 cm3)........... volume of each buffer solution ........................ (10cm3 is more than half of test tube) [1] 1. Volume of Y equal to volume of buffer AND cm 3 on both ; Allow up to 1 decimal place i.e. to 0.1 cm3

4 JPJC/JC2 H2 Biology/Prelims/2023 3 Put the volume of buffer solution labelled pH 3 , stated in (iii), into the test -tube labelled pH 3. 4 Put 1 cm3 of C to the same test-tube. 5 Repeat steps 3 and 4 with each of the other buffer solutions pH 4, pH 5 and pH 6. 6 Stir the yeast suspension Y with a glass rod. 7 Put the volume of Y, stated in (iii), into each test-tube to make the total volume up to the half-way mark. 8 Put a bung or cork into the test-tube and invert the test-tube twice to mix well. Repeat with each test-tube. 9 Immediately start timing. At your selected times, record your observations. You may need to lift each test-tube to eye level to take each reading. Take care not to disturb the contents of the test-tube. (iv) Prepare the space below and record your observations. Table showing the length of halfway mark to top of sediment OR bottom of tube to top of sediment at each time interval pH time / minutes height / mm OR height / mm 3 2 3 37 4 4 36 6 6 34 8 9 31 10 11 29 4 2 2 38 4 3 37 6 4 36 8 7 33 10 10 30 5 2 1 39 4 2 38 6 2 38 8 3 37 10 3 37

5 JPJC/JC2 H2 Biology/Prelims/2023 [Turn over 6 2 1 39 4 1 39 6 1 39 8 1 39 10 1 39 OR time/min height / mm at each pH pH 3 pH 4 pH 5 pH 6 2 4 6 8 10 1. Table with all cells drawn with suitable column / row headings with correct units; pH (at top or left) , time / min(utes), height/length/dept h/AW with mm R: if units anywhere else except headings 2. Collects results for all four pH (ECF if alr penalised in (a)(ii) regarding number of data) ; 3. Recording height to correct precision (whole number) ; 4. Different results/observations for different pH (minimum 2 pH) for final set of data at 10 min ; [4] (v) Use your results to state the effect of pH on the yeast suspension. ............................................................................................................................... [1] 1. (yeast settles) more / higher rate of sedimentation at some pH OR correct example of pH with results ; R: activity OR 2. According to candidates’ results e.g. As pH increases from pH 3 to pH 6, rate of sedimentation increases / there is more sedimentation ; (vi) Identify two significant sources of error in this experiment. ............................................................................................................................... [2] 1. Difficulty in measuring/determining/judging the length/boundary/top of layer (due to bubbles on surface) 2. D ifficulty in lining up the graph paper with the test tube (which might be different for each reading) ; 3. Difficulty in taking readings/adding solutions/mixing solutions at the same time for different pH solutions (so timing was different) ;

6 JPJC/JC2 H2 Biology/Prelims/2023 (vii) Suggest how you could make three improvements to this investigation. ............................................................................................................................... [3] 1. IV: Repeat the experiment with more buffer solutions ; 2. DV: Use ruler with smaller divisions ; 3. DV: Set up each pH separately / stagger timing ; 4. CV: Hold test-tube vertically in retort stand/attach graph paper to test-tubes ; 5. Carry out repeats or replicates ; (viii) Suggest a suitable control that could have been set up for this investigation. ............................................................................................................................... [1] 1. Replace pH solutions with equal volume / (according to (a)(iii) cm3 of distilled water ; [Total: 17]

7 JPJC/JC2 H2 Biology/Prelims/2023 [Turn over 2 Fig. 2.1 is a photomicrograph of a transverse section through part of a stem. magnification × 100 Fig. 2.1

8 JPJC/JC2 H2 Biology/Prelims/2023