TMJC 2023 H2 P4 Ans

1 CANDIDATE NAME CIVICS GROUP _____________________________________________________________________________ H2 BIOLOGY 9744 Paper 4 Practical 24 August 2023 2 hours 30 minutes Candidates answer on the Question Paper. _____________________________________________________________________________ READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name, civics group and 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 and graphs. Do not use staples, paper clips, glue or correction fluid/tape. Answer all questions in the spaces provided on the Question Paper. The use of 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 ___ printed pages Shift Laboratory For examiner’s Use 1 / 17 2 / 16 3 / 22 Total / 55 TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Suggested Answers

2 Question 1 You should read throug h the whole of this question carefully and then plan your use of time to make sure that you finish all that you would like to do. Yeast cells are able to respire both aerobically and anaerobically using glucose as a substrate. You are required to investigate the effect of temperature on the rate of respiration of yeast using a respirometer. A simple respirometer can be made by attaching a length of plastic tubing to a 10 cm 3 syringe, using a short section of rubber tubing. The respirometer may be supported with a retort stand and clamp. Fig. 1.1 shows a simple respirometer containing a yeast suspension. Fig. 1.1

3 In order to introduce the yeast suspension into the simple respirometers, the following steps are used: • Remove a sample of the yeast suspension in 20% glucose solution and place it into a boiling tube. • Make sure that the plunger is pushed fully into the barrel of the syringe. • Insert the plastic tubing into the yeast suspension in a boiling tube. • Withdraw the plunger until the yeast suspension reaches the 5 cm 3 mark on the syringe. • Lift the respirometer so that the glass tubing comes out of the yeast suspension. • Keep the apparatus vertical. Slowly withdraw the plunger so that the yeast suspension rises up the plastic tubing until the suspension is near to the top of the plastic tubing (See Fig. 1.1). • Mark the start position of the meniscus of the yeast suspension. Consider a strategy to allow you to compare the effect of temperature on the rate of respiration of yeast, making use of the apparatus provided. You will need to decide on a suitable range of temperature for this investigation. You are provided with: • simple respirometers • a suspension of yeast cells in a 20% glucose solution that has been maintained at 35°C for at least 15 minutes before the start of the examination • water at 30°C • water at 40°C • crushed ice • hot water at 70°C • a thermometer • a stopwatch • a retort stand. Determine the rate of respiration of yeast by measuring the movement of the meniscus down the plastic tubing.

4 (a) Describe how you will use the apparatus and materials provided to determine the effect of temperature on the rate of respiration. [10] Your plan should: • identify the independent and dependent variables. • Identify the variables you will need to control. • include a control. • have a clear and helpful structure such that the method you use is able to be repeated by anyone reading it, including scientific reasoning behind procedure. • use the correct technical and scientific terms. • include reference to safety measures to minimise any risks associated with proposed experiment. There is no need to describe how to set up respirometer in your methods (It has been described on page 3). 1. Independent & dependent Variables [compulsory – 1 mark each]: (a) Independent variable: Temperature / °C (b) Dependent variable: Distance moved by meniscus in 1 min / mm OR Time taken for meniscus to move 100mm /s 2. Variables to be kept constant and how: (any 1) Concentration of yeast /% or Volume of yeast /cm 3 Obtain yeast suspension from same stock suspension (e.g.20%). Use a syringe to draw fixed volume(e.g. 20cm3) of yeast suspension Diameter of glass tubing /mm Use the same glass tubing / same batch of glass tubings Depends on the dependent variable: Duration of experiment /s Or Distance moved by the meniscus /mm Use a stopwatch to ensure fixed duration e.g.1 min Use a ruler to ensure fixed distance of e.g. 100 mm AVP Rationale: These factors affect the distance moved by the meniscus/time take for meniscus to move (depends on dependent variable) and hence must be kept constant to ensure the accuracy of the experiment .

5 3. [preliminary test] Using the yeast suspension given, set up the respirometer according to given instructions, and allow the reaction to proceed and observe for 2 min. The meniscus should move down the glass tubing. This proves that the yeast is respiring. Proceed with the experiment. 4. Stir the yeast suspension thoroughly with a glass rod [Accept: shake to mix] to ensure a homogenous suspension. 5. R emove 20 cm3 of yeast suspension using syringe in 20% glucose solution and place it into 5 different boiling tubes respectively. [Accept: if student mention other suitable volumes (more than 5cm 3 or pour yeast suspension to certain level, e.g. fill ½ or 2/3 the boiling tube with yeast suspension] 6. Prepare 5 water bath of different temperatures ( 10, 20, 30, 40, 50 °C) using the iced and hot water provided, measured by thermometer. [Accept other temperatures of regular intervals, between 0 to 60°C] 7. Equilibrate yeast suspension by placing a boiling tube in 10°C water-bath [any other temp] for 2 min [Accept: specified timing that is 1min or more]. 8. After 2 min, set up the respirometer with the given instructions (on page 2). Mark the start position for the meniscus, using a marker. 9. [Extra pt]: Withdraw the plunger slightly, to allow the yeast suspension to be higher than the meniscus. 10. Ensure that the respirometer remains vertical throughout the experiment. Either 11. (a) Immediately start time using a stopwatch (when the yeast suspension reached the ‘start’ point) and allow the reaction of proceed for 1 min [accept 30s to 2min]. (b) After 1 min, mark the end position of the meniscus and record the distance moved by the meniscus (between start and stop mark), using a ruler. OR 12. (a) Use a ruler to measure 20 cm [Accept: 5cm to 30cm] from start position and mark the end position. (b) Start the stopwatch and measure the time taken for yeast suspension to move 20cm.

6 13. Repeat steps 2 to 5 using fresh yeast suspension at 10 °C, to obtain 3 replicates, to calculate average, so as to minimize errors and improve accuracy. ‘ Repeat steps 2 to 5 for the other 4 temperatures. Repeat the entire experiment one more time to ensure reproducibility. 14. Control [compulsory]: Replace yeast suspension with equal volume of distilled water at 35°C / at every temperature. This is to show that any movement of the meniscus is due to the production of carbon dioxide during respiration of yeast. 15. Risk and precautions [compulsory]: • Yeast is an irritant to the skin / eyes. Wear gloves / goggles to protect skin / eyes. • Hot water may scald skin. Use mittens, cloth to