2022 J2 ASRJC H2 Biology Prelim Paper 3 (QP)

ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 [Turn over H2 ANDERSON SERANGOON JUNIOR COLLEGE HIGHER 2 2022 JC2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS INDEX NUMBER BIOLOGY 9744/03 PAPER 3 LONG STRUCTURED AND FREE RESPONSE QUESTIONS Candidates answer on the Question Paper. No Additional Materials are required. 15 SEPTEMBER 2022 THURSDAY 2 HOURS READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph Do not use paper clips, highlighters, 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 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 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 23 printed pages and 1 blank page. For Examiner’s Use 1 / 30 2 / 10 3 / 10 4 / 5 / 25 Total / 75

2 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 Section A Answer all the questions in this section. 1 Lactose is a disaccharide found in milk. Lactase , an enzyme found in mammals and some fungi, catalyse the breakdown of lactose. The lactase enzyme is made up of 4 identical polypeptide chains. In humans, molecules of lactase are embedded in the cell surface membrane of epithelial cells lining the small intestine. As the lactose molecules float by in the lumen, they are broken down. (a) Explain how the polypeptide chains in lactase are held together and how they interact with the cell surface membrane. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [3]

3 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 [Turn over Question 1 continues on page 4

4 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 The products of lactose digestion, glucose and galactose , are actively absorbed by intestinal epithelial cells. This absorption is carried out by the sodium-glucose linked transporter (SGLT). SGLT is a secondary active transporter that works together with sodium -potassium (Na+-K+) pump. SGLT transports glucose and galactose concurrently with entry of sodium ions (Na+) into the intestinal epithelial cells. This transport of glucose and galactose uses the driving force generated by the sodium ion gradient created by Na+-K+ pump. Fig. 1.1 illustrates the transport process. Fig. 1.1 Cyanide is a poison that binds with cytochrome oxidase, one of the electron carriers in the mitochondrial membrane. It has been observed that the absorption of glucose and galactose from the lumen of the small intestine is reduced when the intestinal epithelial cells are treated with cyanide.

5 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 [Turn over (b) Using Fig. 1.1 and all the information provided, explain why absorption of glucose and galactose from the lumen of the small intestine is reduced when the intestinal epithelial cells are treated with cyanide. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [4] (c) Many human adults do not produce lactase and are lactose intolerant. This means they cannot digest lactose. Lactose intolerance leads to side -effects such as abdominal pain after eating food containing lactose. Scientists have investigated ways to produce low-lactose cow’s milk from normal cow’s milk for people who are lactose intolerant. One method involved extracting lactase from fungi and mixing the extracted lactase with normal cow’s milk. This method is, however, ineffective because one of the products of lactose digestion, galactose, is an inhibitor of lactase. (i) Explain the effect of galactose on lactase activity. ………………………………………………………………………………………. .……………………………………………………………………………………… ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. [2]

6 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 (ii) Explain why product inhibition is useful when lactase is acting as an intracellular enzyme in fungi cells but can be a disadvantage when extracted lactase is used free in solution for the production of low-lactose cow’s milk. ………………………………………………………………………………………. .……………………………………………………………………………………… ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. [2] Another method of producing low -lactose cow’s milk involved immobilising extracted lactase within alginate beads and putting in high-lactose cow’s milk. As the high-lactose cow’s milk comes into contact with the alginate beads, the immobilised lactase hydrolyses the lactose. Fig. 1.2 shows the set-up. Fig. 1.2 (iii) Suggest how using immobilised lactase for the production of low -lactose cow’s milk helps to reduce the problem of product inhibition. ………………………………………………………………………………………. .……………………………………………………………………………………… [1]

7 ASRJC BIOLOGY DEPT 9744//2022/J2PRELIM/P3 [Turn over A company producing low -lactose cow’s milk carried out an investigation to study the effect of drinking normal high-lactose cow’s milk and the company’s own processed low-lactose cow’s milk. Fig. 1.3 shows the results of the investigation which compares:  the effects on 50 lactose-intolerant volunteers of drinking normal cow’s milk  the effects on the same 50 lactose-intolerant volunteers of drinking low-lactose cow’s milk  the effects on a control group of 15 volunteers, who were not lactose intolerant, of drinking normal cow’s milk. Fig. 1.3 (d) The company claimed that their processed low-lactose cow’s milk is suitable for consumption by lactose-intolerant individuals. With reference to the probability (p) values shown in Fig. 1.3, comment on the validity of the claim. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………