2025 DHS H2 Prelim Paper 1 (with answers)

© DHS 2025 9744/01 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 BIOLOGY 9744/01 Paper 1 Multiple Choice Questions 26 September 2025 Additional Materials: Multiple Choice Answer Sheet 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your centre number, index number, name and class at the top of this page. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of 24 printed pages.

2 © DHS 2025 9744/01 1 The electron micrograph shows a part of a cell found in the pancreas. Identify organelle P and its related function in the pancreatic cell. Organelle P Function A Golgi vesicle Packaging of misfolded proteins for degradation B Transport vesicle Transporting synthesized lipids to the rough ER C Secretory vesicle Storing and secreting digestive enzymes or hormones D Ribosome Initiating protein synthesis after attachment

3 © DHS 2025 9744/01 [Turn over 2 A researcher is studying the properties of a toxin produced by a plant. When cellular contents are exposed to the toxin, the cell will die. The table shows the relative percentages of various organelles , in cells that are not actively producing the toxin and cells that are actively producing the toxin. cell structure description relative percentage of cell / % non-toxin producing cell toxin producing cell V double membrane bound organelle with cristae 12 15 W sheet-like, single membrane bound organelle with continuous lumen 15 20 X single membrane bound organelle arranged in tubules 14 3 Y large, dense, and contains rRNA 3 10 Z single membrane bound organelle that does not contain phospholipids in the lumen 35 46 Which statement is consistent with the data provided? A Toxin production in structure V is energy -intensive, suggesting that the toxin is lipid - soluble. B Protein synthesis is upregulated in structure W, implying that the toxin is protein-based and lipid-soluble. C Increased ribosome production in structure Y suggests the toxin is RNA -based and water-soluble. D Structure Z stores the water-soluble toxin.

4 © DHS 2025 9744/01 3 The diagram shows the monosaccharide xylose. Xylan is a structural polysaccharide made from mainly xylose residues and is found in cell walls of many flowering plants and grasses. It has a similar structure to cellulose. Which diagram shows the formation of a glycosidic bond between two xylose monomers in xylan? A B C D

5 © DHS 2025 9744/01 [Turn over 4 Which flow chart outlining the test for non-reducing sugars is correct? A Add alkaline sodium hydrogencarbonate to sample Neutralise with dilute hydrochloric acid Add Benedict’s solution and boil B Add alkaline sodium hydrogencarbonate to sample Neutralise with dilute hydrochloric acid Add Biuret solution and boil C Boil sample with dilute hydrochloric acid Neutralise with dilute sodium hydrogencarbonate Add Benedict’s solution and boil D Boil sample with dilute hydrochloric acid Neutralise with dilute sodium hydrogencarbonate Add Biuret solution and boil 5 In an experiment, fluorescent dyes were attached to proteins on the outer surface of cell surface membranes. Fluorescent dyes of one colour were attached to proteins of a living human cell and fluorescent dyes of a different colour were attached to proteins of a living mouse cell. The human cell and the mouse cell were then fused to form a hybrid cell. At first, the proteins attached to different fluorescent dyes remained separate, but after 40 minutes the proteins were distributed randomly across the hybrid cell surface membrane. A student made four conclusions based on the result of this ex periment. How many conclusions are correct? • Proteins are found only on the outer surface of cell surface membranes. • Proteins in the outer layer of a bilayer do not penetrate into the inner layer. • Proteins move freely in the phospholipids of a bilayer. • The cell surface membranes of the two cells are bilayers. A 1 B 2 C 3 D 4

6 © DHS 2025 9744/01 6 Which statement best describes a structural similarity between collagen and cellulose that contributes to their function? A Both rely on covalent cross -links within their monomers to resist tensile forces and provide rigidity. B Both collagen and cellulose have parallel, linear chains held together by extensive hydrogen bonding, forming strong fibrils that give them high tensile strength. C Both are largely insoluble due to hydrophobic interactions, ensuring structural durability. D Both consist of polypeptide chains forming hydrogen bonds between adjacent molecules. 7 During lung infections, phagocytes move from the blood to the epithelial lining of the alveoli. Phagocytes release the enzyme elastase (a protease) which digests a pathway through the alveolar wall. A glycoprotein, alpha 1-antitrypsin (AAT), is often produced in the lung to inhibit elastase and hence prevent widespread breakdown of the alveoli. An investigation was conducted to study the effect of AAT on trypsin activity. The experiment measured the rate of protein digestion by trypsin under different conditions. The results are shown in the table below. Condition Relative Rate of Protein Digestion by Trypsin (%) Trypsin alone 100 Trypsin + excess substrate 100 Trypsin + AAT 20 Trypsin + AAT + Excess substrate 95 Based on the information, which conclusion best explains how AAT inhibits trypsin? A AAT binds to the substrate, preventing it from interacting with the active site of trypsin. B AAT binds irreversibly to the active site of trypsin, permanently inactivating the enzyme. C AAT has a similar charge and shape to the substrate, allowing it to compete for binding at the active site of trypsin. D AAT alters the shape of trypsin's active site through allosteric regulation, preventing substrate binding.

7 © DHS 2025 9744/01 [Turn over 8 Cells can regulate their membrane composition to maintain appropriate fluidity under different environmental conditions. In an investigation on membrane fluidity in bacterial cells, three variables influencing membrane fluidity were measured under different temperature conditions. Variable Condition A Condition B Percentage of saturated fatty acids 18.2 12.5 Average number of double bonds per lipid molecule 4.2 4.8 Cholesterol to phospholipid ratio 2.5 1.8 Which statement correctly identifies Condition A and provides the appropriate explanation? A Hot temperatures; a higher proportion of unsaturated fatty acids reduces excessive membrane fluidity at elevated temperatures. B Cold temperatures; a higher cholesterol-to-phospholipid ratio helps maintain membrane integrity by preventing excessive solidification. C Hot temperatures; an increased number of double bonds allows for tighter phospholipid packing at high temperatures. D Cold temperatures; a higher proportion of saturated fatty acids prevents