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 o f the reaction is studied to determine the optimal conditions for product formation. Explain how substrate concentration can affect the rate of an enzyme-catalysed reaction.[4] 1. At low substrate concentration, substrate concentration is limiting/ the limiting factor. 2. as substrate concentration increases, there is an increase in frequency of effective collisions between enzymes and substrates which results in a higher rate of enzyme-substrate complex formation as more active sites are occupied by substrates 3. At higher substrate concentration, enzyme saturation is reached, where all active sites are occupied by substrate molecules at any one time. 4. Thus, enzyme concentration becomes limiting/ is the limiting factor and substrate concentration is no longer limiting . Further increase in substrate concentration will not cause the rate of reaction to increase further. [Total: 10]

4 ©EJC 2024 9744/02/J2H2PRELIM/2024 2 Lysosomes are cell structures that contain acid hydrolases which are enzymes that work best in acidic environments. Fig. 2.1 shows some processes that occur in neutrophils. Fig. 2.1 (a) Name the cell structures labelled A and E. [1] A - Rough endoplasmic reticulum (R: RER) E - Golgi apparatus / Golgi body (b) State the function of F. [1] 1. Transport proteins, such as acid hydrolases, from RER to Golgi apparatus (A: from A to E) 2. compartmentalize proteins, such as acid hydrolases (idea of separating from the rest of cell). 3. [Any one]

5 ©EJC 2024 9744/02/J2H2PRELIM/2024 [Turn over (c) Describe the role of cell surface membrane during process C. [3] 1. Receptors on the cell surface membrane of neutrophils recognize and bind to bacteria / antigen / epitope R: (constant region of) antibody on bacteria (opsonization) – not seen in Fig. 2.1 2. Pseudopodia of cell surface membrane wrap around/engulf/enclose bacteria before fusing 3. To form phagosome/phagocytic vesicle/ vesicle in phagocytosis (R: endosome and endocytosis + cell surface membrane invaginates/infolds as neutrophil is a phagocyte) (d) With reference to the processes occurring at B and at D in Fig. 2.1, outline the roles of acid hydrolases in lysosomes. [4] 1. Acid hydrolases in lysosomes hydrolyse/digest/break down/destroy worn out / damaged organelles, such as mitochondria, in autophagy 2. For biological molecules to be recycled or reused within the cell (OWTTE) 3. Acid hydrolases catalyse hydrolysis/digestion/break down of bacteria 4. Any named example of acid hydrolase, substrate and bond (max 2): e.g.  Lysozyme hydrolyses glycosidic bonds in peptidoglycan cell wall of bacteria  Nuclease hydrolyses phosphodiester bonds in bacterial nucleic acids  Protease hydrolyses peptide bonds in bacterial proteins R: digest / break down bond R: process antigens into short peptides to be loaded onto MHC protein to form peptide- MHC complex for antigen presentation to naïve T cells (neutrophils are not antigen- presenting cells) The acid hydrolases in lysosomes refer to the hydrolytic enzymes found in the a cidic internal environment of lysosome. (e) Carrier proteins in the membranes of lysosomes maintain a lower pH than the surrounding cytoplasm by moving hydrogen ions. Suggest how the carrier proteins maintain the lower pH within the lysosomes. [1] 1. Pump hydrogen ions / protons into lysosome against concentration gradient via active transport (R: facilitated diffusion) [Total: 10]

6 ©EJC 2024 9744/02/J2H2PRELIM/2024 3 The early development of an animal involves divisions of the zygote and daughter cells by mitosis to form an embryo consisting of genetically identical cells. Fig. 3.1 shows several cells at different stages of the cell cycle in an embryo of whitefish, Coregonus artedi. Fig. 3.1 (a) (i) Name the stage of mitosis in cell A and in cell C, shown in Fig. 3.1. [2] A – Metaphase C – Telophase (NOT anaphase or cytokinesis) (ii) Describe the role of microtubules in cell B. [2] 1. Shortening of kinetochore microtubules to pull daughter chromosomes (R: sister chromatids) apart towards opposite poles of cell 2. Non-kinetochore microtubules extend to elongate the cell]

7 ©EJC 2024 9744/02/J2H2PRELIM/2024 [Turn over (b) Uncontrolled mitosis can cause cancer in humans. Paclitaxel is a drug used in the treatment of some forms of cancer. Researchers investigated the effect of Paclitaxel on the mitotic cell cycle of cancer cells.  The cancer cells were grown for two days and then divided into groups.  Each group was treated with a