NJC 2023 SH2 H2 Biology Paper 4 Student

© NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination [Turn over NATIONAL JUNIOR COLLEGE, SINGAPORE Senior High 2 Preliminary Examination Higher 2 CANDIDATE NAME BIOLOGY CLASS 2bi2_____ REGISTRATION NUMBER Biology Paper 4 Practical 9744/04 17 August 2023 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name, Biology class, and registration number on all the work you hand in. Give details of the practical shift and laboratory in the boxes provided. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs. Do not use staples, 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 workings 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 the brackets [ ] at the end of each question or part of question. Shift 1 2 3 Laboratory BI23 BI24 CM43 CM44 For Examiner’s Use 1 19 2 17 3 19 Total 55 This document consists of 18 printed pages and 2 blank pages.

2 © NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination Answer all questions. 1 Baker’s yeast, Saccharomyces cerevisiae, converts sugars to ethanol and carbon dioxide under anaerobic conditions. You will investigate the effects of different concentrations of ethanol on the rate of respiration in yeast. (a) Describe and explain the expected effect of increasing ethanol concentration on the rate of respiration in yeast. [4] You will set up the apparatus as shown in Fig. 1.1. Fig. 1.1 rubber tubing yeast, sucrose, and water and/or ethanol

3 © NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination [Turn over You are provided with: • 5.0 g dried yeast Y, in a container labelled Y • 10.0 g sucrose S, in a container labelled S • 120 cm3 5.0 % ethanol E1, in a container labelled E1 • 120 cm3 10.0 % ethanol E2, in a container labelled E2 • 200 cm3 distilled water W, in a beaker labelled W E1 and E2 contain ethanol, which is harmful and flammable. Suitable eye protection should be worn. The lid on the plastic vial should be kept on, when not in use. Read steps 1-11. Proceed as follows. 1 Set up a water bath and maintain it at about 37 °C. 2 Measure 100 cm3 of W and pour it into a conical flask. 3 Weigh 1.0 g of Y and 2.0 g of S and add them to the conical flask. Shake to mix the content. 4 Incubate the conical flask in the water bath for 5 minutes. 5 Fill the burette with water. Invert the burette and clamp it on a retort stand, as shown in Fig 1.1. 6 Attach the rubber bung (with the rubber tubing) to the conical flask. 7 Insert the rubber tubing through the open end of the burette. Ensure that the apparatus is set up as shown in Fig. 1.1. 8 After 5 minutes of incubation, note the initial volume of water in the burette. 9 Measure the volume of carbon dioxide given off for 8 minutes by the amount of water displaced. 10 Repeat steps 1-9 using 100 cm3 of E1. 11 Repeat steps 1-9 using 100 cm3 of E2.

4 © NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination (b) Record your results in an appropriate table. [3] (c) Use the grid provided to display your results. [4]

5 © NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination [Turn over (d) Without quoting numerical values, explain how this experiment allows you to m onitor respiration in yeast. [3] (e) Describe two main sources of error in the procedure and discuss how they may reduce the confidence in your results recorded in (b). [4] (f) Suggest a negative control for this experiment to prove the action of yeast in converting sugars to ethanol and carbon dioxide. [1] [Total: 19]

6 © NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination 2 Fig. 2.1 shows Elodea canadensis (Canadian pondweed) which is an aquatic plant commonly used in aquarium tanks to help control algae and keep the water clear. Fig. 2.1 Fig. 2.2 shows how Elodea form dense mats on the surface of water in an aquarium tank. Fig. 2.2 Studies suggest that one mechanism by which Elodea inhibits algae is via competing for light for photosynthesis.

7 © NJC 2023 9744/04/SH2/H2 Biology/Preliminary Examination [Turn over (a) (i) Design an experiment to show that the rate of photosynthesis in Elodea is dependent on light intensity. In your plan you must use: • a room which can be made dark • table lamp • Elodea (Canadian pondweed) • ruler • scalpel • sodium hydrogen carbonate powder • weighing balance • measuring cylinder • distilled water • boiling tube • delivery tube • gas syringe • rubber bung • thermometer • stopwatch • beaker • retort stand Your plan should: • identify the dependent variable and independent variable • identify variables you will need to control • have a clear and helpful structure so that the method described could be repeated by anyone reading it • be illustrated by relevant diagrams, if necessary • include details to ensure that results are accurate and repeatable as possible • indicate how results will be recorded and analysed • use the correct technical and scientific terms • include reference to safety measure to minimi se any risks associated with the proposed experiment

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