NCHS_Bio_P3

1 Name: Register Number: Class: PRELIMINARY PRACTICAL ASSESSMENT 2021 SECONDARY FOUR EXPRESS SCIENCE (BIOLOGY) 3 Aug 2021, Tuesday Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your name, class and index number in the spaces provided on the question paper. Write in dark blue or black pen. You may use a pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions If working is needed for any question it must be shown with the answer. Omission of essential working will result in loss of marks. Calculators should be used where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. The total marks for this paper is 15. This paper consists of 5 printed pages including the cover page.

2 You are advised to read the whole question before you start. 1(a) Yeasts are unicellular fungi that can survive both in the presence and absence of oxygen. In the presence of oxygen, yeasts undergo aerobic respiration, breaking down carbohydrates into carbon dioxide and water. In the absence of oxygen, yeasts undergo a naerobic respiration and break down carbohydrates into carbon dioxide and alcohol. You are provided with glucose solution, and a suspension of yeast. You will compare the metabolism of glucose in this species of yeast at two different temperatures. Use the following method: Step 1 Label 2 test tubes A and B. Step 2 Using tap water and the hot water provided, prepare a beaker half -filled with water at room temperature, 30 -32oC. The temperature of the water in the beaker should be maintained at this temperature throughout the experiment. Step 3 Using a spatula, gently stir the suspension of yeast in the beaker labelled ‘yeast’. Add 4 cm3 of this yeast suspension to test tube A using a syringe. Step 4 Add 1 cm3 of glucose solution (labelled G) into test tubes A and gently shake the mixture. Step 5 Place test tubes A into the beaker of water at 35 oC for 2 minutes. Step 6 During the 2-minute waiting time, prepare a test tube half-filled with water. Step 7 Connect the rubber bung and delivery tube to test tube A only, as shown below. Step 8 Submerge the open end of the delivery tube into the test tube of water. Step 9 Count the number of gas bubbles produced in the test tube of water in the next 2 minutes.

3 Step 10 Draw a table in 1(a)(i) to record the number of bubbles produced. Step 11 Remove the rubber bung and delivery tube from test tube A. Step 12 Prepare a water bath with the temperature of 70oC. The temperature should be maintained at 70oC throughout the experiment. Step 13