NJC 2023 SH2 H2 Biology Paper 4 Mark Scheme

© NJC 20239744/04/SH2/H2 Biology/Preliminary Examination[Turn over H 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

2 © NJC 20239744/04/SH2/H2 Biology/Preliminary Examination This document consists of 18 printed pages and 2 blank pages.

3 © NJC 20239744/04/SH2/H2 Biology/Preliminary Examination[Turn over 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. As the concentration of ethanol increases, the rate of respiration decreases; Ethanol is organic and thus dissolves and disrupts phospholipid bilayer; This destroys the integrity of membrane essential for respiration, namely the inner mitochondrial membrane; Membrane proteins such as electron carrier and ATP synthase on the inner mitochondrial membrane become non-functional; Enzymes are also denatured by the high ethanol concentration by the disruption of hydrogen bonding or hydrophobic interactions; High concentration of ethanol inhibits anaerobic respiration / leads to end product inhibition thus there is a decrease in CO2 released; R: Change in pH, decrease in frequency of effective collision (ethanol is not within the cell) [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

4 © NJC 20239744/04/SH2/H2 Biology/Preliminary Examination 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 % ethan