VJC 2023 H2 9744 P3 QP

1 VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION HIGHER 2 CANDIDATE NAME: ……………………………………………………….………………. CT GROUP: ………………..……… BIOLOGY Paper 3 Long Structured and Free-response Questions 9744 /03 20 September 2023 2 hours Candidates answer on the Question Paper. No Additional Materials are required. This document consists of 22 printed pages and 2 blank pages. [Turn over] READ THESE INSTRUCTIONS FIRST Write your name and CT group in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question in the space 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 working or if you do not use appropriate units. The number of marks is given in bracket [ ] at the end of each question or part question. For Examiner’s Use Section A 1 /28 2 /12 3 /10 Section B /25 Total

2 Section A Answer all the questions in this section. 1 Cells respond to changes in their internal as well as external environment. Unicellular eukaryotes such as yeasts respond to changes in the glucose concentration in the environment. Glucose is the preferred carbon source for Baker’s yeasts (Saccharomyces cerevisiae) which metabolises glucose by a purely glycolytic process (fermentation), producing ethanol even under aerobic conditions. Presence of glucose represses the uptake and metabolism of other carbon sources such as galactose and maltose. When the glucose has been consumed, the cell switches to aerobic metabolism of the ethanol. (a) (i) State the difference in the number of ATP produced from one molecule of glucose between fermentation and aerobic respiration. [1] (ii) Suggest why yeast cells undergo fermentation even in the presence of oxygen. [2]

3 (b) Several components of the signalling pathway involved in glucose repression in yeast have been identified. These are shown in Fig.1.1 . Snf1 is a protein kinase and binding of Mig1 to the promoter interferes with the binding of other proteins. Fig 1.1 (i) With reference to the information given in Fig 1.1, explain how the presence of glucose in the environment is able to bring about the repression of GAL1 gene. [4]

4 Mig1 binds to promoter sites with these features: ● 17 base pairs long ● Includes a region of five repeating adenine-thymine pairs ● Includes a region of six repeating cytosine-guanine pairs Promoter sites to which Mig1 binds are known as Mig1-binding promoter sites. (ii) Explain how Mig1 recognises and binds to these sites. [2] Scientists analysed the yeast genome to look for DNA that matc