2024 NJC H2 Bio P4 MS

© NJC 20249744/04/SH2 Preliminary Examination[Turn over H NATIONAL JUNIOR COLLEGE, SINGAPORE Senior High 2 Preliminary Examination Higher 2 CANDIDATE NAME MARK SCHEME BIOLOGY CLASS 2bi2_____ REGISTRATION NUMBER Biology Paper 4 Practical 9744/04 26 August 2024 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 CM42 CM43 CM44 For Examiner’s Use 1 20 2 20 3 15

2 © NJC 20249744/04/SH2/H2 Biology/Preliminary Examination Total 55 This document consists of 19 printed pages and 1 blank pages.

3 © NJC 20249744/04/SH2/H2 Biology/Preliminary Examination Answer all questions. 1 Yeast can convert different respiratory substrates into carbon dioxide via cellular respiration. You will investigate the effect of different respiratory substr ates on the rate of respiration in yeast. Hydrogencarbonate indicator is a pH indicator which can be used to measure the amount of carbon dioxide produced by the respiring yeast cells. When carbon dioxide dissolves in water, carbonic acid is formed, reducing the pH and changing the colour of the indicator solution. The initial pH of the reaction mixture containing yeast and respiratory substrate may be slightly different depending on the type of respiratory substrate. This can be standardised by using sodium bicarbonate solution to adjust pH so that the starting c olour corresponds to the colour number 6 on the hydrogencarbonate indicator colour chart provided. You are provided with: ● yeast suspension, labelled Y ● alginate solution, labelled A ● calcium chloride solution, labelled C ● respiratory substrate 1, labelled S1 ● respiratory substrate 2, labelled S2 ● respiratory substrate 3, labelled S3 ● hydrogencarbonate indicator, labelled H ● sodium bicarbonate solution, labelled B ● hydrogencarbonate indicator colour chart Read steps 1–12 before starting the investigation. Proceed as follows. 1 Add about 30cm 3 of C into a 50cm3 beaker. 2 Stir Y to suspend the yeast cells. Transfer 3.0cm3 of Y into another 50cm3 beaker. 3 Add 6.0cm3 of A into the beaker containing Y, taking care not to introduce air bubbles into the