2023 CJC Prelim H2 Bio 9744 P4.ANS (for sharing)

9744 / 04 / Prelim Examination / 2023 NAME: ________________________________________ CLASS: _________ INDEX: __________ CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 BIOLOGY 9744 / 04 Paper 4 Practical 25 August 2023 2 hours 30 min Candidates answer on the Question Paper Additional Materials: READ THESE INSTRUCTIONS FIRST Write your 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 a 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. This document consists of XX printed pages and X blank page. [Turn over Shift Laboratory For Examiner’s Use 1 2 3 TOTAL MARKING SCHEME

2 9744 / 04 / Prelim Examination / 2023 Answer all questions. 1 During photosynthesis in leaves, carbon dioxide enters through stomata and diffuses through intercellular air spaces to the mesophyll. Leaf discs submerged in solution can be used to investigate photosynthesis. To investigate the effect of carbon dioxide concentration on the rate of photosynthesis in leaf discs, you will: • prepare different concentrations of sodium hydrogencarbonate solution, as a source of dissolved carbon dioxide. • measure the rate of photosynthesis by recording the time taken for submerged leaf discs to reach the surface due to the build-up of oxygen in the air spaces. You are provided with: • 30 cm3 of 10.0 g dm–3 sodium hydrogencarbonate solution, labelled H1 • distilled water, labelled W • fresh, green leaves from plant species A, in a Petri dish labelled A (a) Carry out a serial dilution of the 10.0 g dm –3 sodium hydrogencarbonate solution, H1, to reduce the concentration of the sodium hydrogencarbonate solution by half between each of three successive dilutions, to give H2, H3 and H4. You are required to make up a sufficient volume of each concentration of sodium hydrogencarbonate solution in the specimen tubes provided so that, once the serial dilution has been completed, there is at least a volume of 10 cm3 for each solution. (i) Complete Fig. 1.1 on page 3 to show how you will carry out your serial dilution. For each specimen tube, • draw one curved arrow with a label, above the specimen tube, to show the volume and concentration of hydrogencarbonate solution added from the previous tube. • state the volume of W added to prepare the concentration. • state, under the specimen tube, the volume and concentration of hydrogencarbonate solution left for use in the investigation.

3 9744 / 04 / Prelim Examination / 2023 Fig. 1.1 [3]

4 9744 / 04 / Prelim Examination / 2023 Mark Allocation [C1] Correct final concentrations of 5.00, 2.50, 1.25 [Ignore d.p] with correct labelling of H1, H2, H3 and H4 at the bottom of each specimen tube [C2] Correct volumes and concentration to make up at least 10.0 cm 3 of H2, H3 and H4 (after all dilutions completed) and remaining volume left to use for all solutions are ≥ 10 cm3) [Note: for H4, volume remaining is either 20.0 cm3 (if there is not further removal) or 10.0 cm3 if there is volume removed] [P] All volumes to be listed / given to 1 d.p. and concentrations given to 3 s.f.

5 9744 / 04 / Prelim Examination / 2023 Read steps 1–14 and prepare the table in (a)(iii) before proceeding. 1 Using a plastic drinking straw, cut out a leaf disc by placing an open end of the straw on a leaf from plant species A, while supporting the leaf from behind with your finger. Push the straw through the leaf on to your finger to cut out a disc. The disc wi ll stick onto the end of the straw. Repeat until you have 12 leaf discs of uniform size. 2 Place the discs in a Petri dish containing distilled water, W. You may need to tap the straw a few times to detach the discs. 3 Remove the plunger of a 10 cm3 syringe. 4 Place all the leaf discs in the barrel of the syringe, using forceps. Make sure that the leaf discs are at the bottom of the syringe barrel. Replace the plunger of the syringe and push it down until it almost touches the leaf discs. 5 Draw up 5 cm3 of distilled water, W, from the Petri dish into the syringe. 6 Turn the syringe so that the nozzle is pointing upwards and tap the sides so that air bubbles rise to the top. Push the plunger in until the nozzle of the syringe is filled with water. 7 Place a finger tightly over the nozzle of the syringe to form an airtight seal. Firmly draw out the plunger as far as you can, as shown in Fig. 1.2, and then gently allow the plunger to return to its starting position. Fig. 1.2 8 Remove your finger from the nozzle and shake the syringe gently or tap the side to remove gas bubbles. The leaf discs should sink. 9 If discs are still floating on the surface, repeat steps 6-8 until nearly all leaf discs have sunk. You may have to repeat steps 6-8 several times. (ii) State the purpose of steps 6 to 8. …………………………………………………………………………………………..…… ……………………………………………………………………………………..………… ……………………………………………………………………………..………………... [1]

6 9744 / 04 / Prelim Examination / 2023 To remove any gases from the air spaces in the leaf discs (so that they will sink in sodium hydrogencarbonate solution) [Reject: ref. to gases on the outside / surrounding] 10 Carefully pull the plunger out of the syringe and pour the water and leaf discs back into the Petri dish. If any leaf discs remain in the syringe, use the glass rod to remove them. 11 Put one leaf disc into each of the specimen tubes containing the same volume of sodium hydrogencarbonate solutions. Swirl each tube and use a glass rod to push the leaf disc to the bottom. If any leaf disc floats it should be removed and replaced with a fresh leaf disc that sinks. 12 When all specimen tubes contain a leaf disc that has sunk to the bottom, p lace the specimen tubes 10 cm from a bench lamp. 13 Switch on the bench lamp and start a stopwatch. 14 Record the time taken for each leaf disc to reach the surface, in (a)(iii). If any leaf discs have not reached the surface after 15 minutes, record ‘more than 900’. (iii) Record your results in a suitable table in the space below. Concentration of sodium hydrogen carbonate solutions / g dm–3 Time taken for leaf disc to reach the surface / s 10.0 Shortest 5.00 2.50 1.25 Longest [H] – ruled table drawn, with Independent Variable on the leftmost column and with appropriate & correct column headings and units for both independent and dependent variables: - Concentration of sodium hydrogen carbonate solutions / gdm–3 - Time taken for leaf disc to reach the surface / s [Reject: short forms used for concentration; ‘sec’ instead of ‘s’ for seconds] [O] – Record all 4 concentrations to 3 sig. fig. and time as whole number; no units in body of table [T] – Correct Trend (records shortest time for the highest concentration of sodium hydrogencarbonate solution (H1), increasing time as concentration of sodium hydrogencarbonate decreases to minimu