2024 EJC Prelim Biology P2 (A)

©EJC 2024 9744/02/J2H2PRELIM/2024 [Turn over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examinations 2024 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME ANSWERS CIVICS GROUP 2 3 - REGISTRATION NUMBER H2 Biology Paper 2 Structured Questions 9744/02 11 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on all the work you hand in. Candidates are to answer: All questions on the Question Paper. Write your answers in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue, or correction fluid/tape. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 29 printed pages and 3 blank pages. For Examiner’s Use 1 2 3 4 5 6 7 8 9 10 11 Total

2 ©EJC 2024 9744/02/J2H2PRELIM/2024 Answer all questions. 1 The unicellular fungus Kluyveromyces lactis is found in dairy products. It is a safe microorganism to culture for the extraction of the enzyme lactase. Lactase catalyses the breakdown of lactose, a sugar found in milk. The reaction catalysed by lactase is summarised in Fig. 1.1. Fig. 1.1 (a) Describe the reaction that is catalysed by lactase. Use Fig. 1.1 to help you. In you r answer, identify Y and product Z. [3] 1. To hydrolyse glycosidic bond / β-1,4 glycosidic bond broken R: if bond type is incorrectly named 2. With the addition of Y: water; 3. To hydrolyse lactose to galactose and Z (α-glucose) R: glucose (b) On a commercial scale, immobilised lactase can be used to produce lactose-free milk. One of the products of the reaction shown in Fig. 1.1 acts as an inhibitor of lactase. This is an example of product inhibition. (i) Suggest why product inhibition is advantageous in K. lactis when lactase is acting as an intracellular enzyme but can be a disadvantage when extracted lactase is used free in solution to produce lactose-free milk. [2] 1. Advantage: It allows for homeostatic control/ maintainance / efficient metabolism; AVP e.g. if, (enough) glucose/ galactose/ monosaccharides, present then no need for, uptake/ breakdown, of lactose avoids osmotic problems as no build-up of monosaccharides 2. Disadvantage: It results in reduced productivity / slows rate of reaction as enzyme is unnecessarily inactivated; AVP (ii) Suggest how using immobilised lactase for the production of lactose-free mi lk helps to reduce the problem of product inhibition. [1]

3 ©EJC 2024 9744/02/J2H2PRELIM/2024 [Turn over 1. products and enzyme kept separated OR product removed immediately; (c) When developing an enzyme-catalysed reaction for use in industry, the progress