TJC 2023 H2 Prelim P4 ANS Sharing

1 [TURN OVER TEMASEK JUNIOR COLLEGE 2023 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER BIOLOGY 9744/04 Paper 4 Practical 30 August 2023 2 hour 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. 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 16 printed pages. Shift Laboratory For Examiner’s Use 1 / 17 2 / 17 3 / 21 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 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.

2 Answer all questions. 1 (a) You will investigate the effect of different temperatures on the permeability of the cell surface membrane of beetroot cells. Beetroot is a vegetable that contains a red pigment in its cells. When beetroot tissue is put into water, the red pigment can move out of the cells through the cell surface membrane, changing the water to a red colour. You are provided with: labelled contents hazard volume / cm 3 B 4 pieces of beetroot none - W distilled water none 100.0 The red pigment in beetroot cells can stain clothing and skin. Use blunt forceps to handle beetroot tissue and, if any pigment comes into contact with your skin, wash it off immediately under cold water. It is recommended that you wear suitable eye protection. You will need to:  put beetroot tissue in water at different temperatures  leave the beetroot tissue in the water for a period of time  record the intensity of colour in the water at each temperature. (i) The temperature range that you will use must include a minimum temperature of 25˚C and a maximum temperature of 65˚C. State other temperatures that you will use in your investigation. [1] 35˚C, 45˚C, 55˚C  Must have at least 3 other temperatures between the range  Must have regular intervals Read step 1 to step 13 before proceeding. Proceed as follows. 1 Cut the beetroot pieces into 2 mm thick discs. You will need at least 25 discs. 2 Put all the discs that you have cut into the beaker labelled D and cover them with approximately 30 cm3 distilled water, W. 3 Stir with a glass rod. 4 Pour off the water into the beaker labelled For waste, leaving the discs in the beaker labelled D. 5 Put all the discs on a paper towel and blot them to remove excess water.

3 [TURN OVER 6 Set up and maintain a water-bath at 25˚C, using the beaker labelled water-bath. The water- bath will be needed in step 9. 7 Put five discs into one test-tube. 8 Put 10 cm3 of distilled water, W, into the test-tube with the five discs. 9 Put this test-tube into the water-bath for four minutes. You will need to maintain the water-bath at the correct temperature throughout these four minutes. 10 After four minutes, remove the test-tube with the discs from the water-bath. 11 Pour the water from this test-tube into a second test-tube, leaving the discs in the first test-tube. 12 Repeat step 1 to step 11 until all of the temperatures stated in (a)(i) have been tested, finishing with the maximum temperature of 65˚C. 13 Observe the colour intensity of the water in each of the test-tubes in the test-tube rack. 14 Using only the symbols shown in Table 1.1 to represent intensity of colour, decide the intensity of colour in each of the test-tubes in the test-tube rack. Record your results in (a)(ii). Table 1.1 intensity of colour symbol dark red ++++++ decreasing intensity of red colour +++++ ++++ +++ ++ no colour + (ii) Record your results in an appropriate table, using only the symbols shown in Table 1.1. Temperature / °C Intensity of colour 25 + 35 ++ 45 +++ 55 ++++ 65 +++++ CH – Column heading with units, no units in table D – record data for all 5 temperatures (ecf (a)(i)), no repeated data Tr – Temperature increase, intensity increase (look at 25, and 65) P – only symbols [4]

4 (iii) Use your knowledge of cell surface membranes to explain the results that you recorded in (a)(ii). [3] General ideas: 1. Reference to phospholipid bilayer / fatty acid tails 2. Reference to proteins denatured 3. Increased fluidity of membrane 1. Cell surface membrane is made up of a phospholipid bilayer 2. As temperature increases, more proteins in the membrane will be denatured, 3. Membrane will be more fluid, allowing more pigment to exit the cell. (iv) Identify three significant sources of error in this investigation. [3] (v) Suggest how you would make improvements to reduce two of the sources of error identified in (a)(iv). [2] Source of error [3] Improvement [2] 1. Difficult to identify intensity of colour, subjective and prone to human error. Note: ½ mark if “intensity” is missing. 1. Use a colorimeter to detect intensity of colour 2. Difficult to maintain temperature throughout the experiment. R: Temperature not maintained (step 9). 2. Use thermostatically-controlled water- bath. 3. Not all pigment removed from beetroot tissue. These pigments would diffuse into the distilled water before the experiment resulting in inaccuracy. 3. Wash beetroot several times until no red colour in water. 4. Difficult to accurately cut 2 mm thick discs resulting in discs with different total surface area. 4. Use vernier caliper to measure 2 mm. Accept: Prepare thicker discs (e.g., 5mm) which are easier to measure and cut accurately. 5. Beetroot pieces were prepared from different beetroot in which the amount of pigments might differ from each other. 5. Ensure beetroot pieces provided were from the same beetroot.

5 [TURN OVER 6. Difficult to identify intensity of colour, subjective and prone to human error 6. Use a colorimeter to detect intensity of colour 7. Difficult to maintain temperature 7. Use thermostatically-controlled water- bath 8. Not all pigment removed from beetroot tissue before experiment 8. Wash beetroot several times until no red colour in water 9. Difficult to accurately cut 2 mm thick discs 9. Use vernier caliper to measure 2 mm (b) A scientist investigated changes in the mean width of stomata in the leaves of a plant growing in hot, dry conditions. The scientist measured the widths of stomata at different times of day, from dawn to midnight. Fig. 1.1 shows where the scientist measured the width of each stoma. Fig. 1.1 The scientist calculated the mean width of stomata for each time of day. The results are shown in Table 1.2. Table 1.2 time of day mean width of stomata / arbitrary units (au) dawn 86 morning 36 noon 10 evening 6 midnight 95

6 Use the grid provided to plot a graph in an appropriate form to display the data shown in Table 1.2. [4] 1. S: (x-axis) even width of bars; (scale on y-axis) label every 10 squares; 2. P: correct plotting of five bars; bars in order of table; equal spacing between bars; 3. A: (x-axis) time of day; (y-axis) mean width of stomata / au; 4. BF: five separate bars; bars drawn with even lines; labelled appropriately; R: shading of bars [Total: 17] time of day mean width of stomata / arbitrary units (