Jurongville Pure Biology Prelim 2024 Paper 1 & Paper 2 Answer

Jurongville Secondary School Science Department 2024 Marking Scheme & Marker’s Report Assessment: Preliminary Examination Biology P2 (6093) Level: 4 Express Qn Marking Scheme Remarks Marks 1ai 1: brown 2: colourless Accept 1: colourless if explained in 1aii about optimum pH of enzyme being acidic [1] [1] 1aii 1. In test-tube 1, phenol can bind with active site of polyphenol oxidase to form enzyme-substrate complex and hence break down to form melanin, which is brown; 2. In test-tube 2, polyphenol oxidase is denatured; 3. The 3D shape of the active site will be altered and will no longer be able to fit the substrate of phenol; Also accept if 1 colourless, but explains that from 3, optimum pH for enzyme seems acidic. (however at normal conditions, the break down is still catalysed, so original marking scheme still valid) [1] [1] [1] 1b Polyphenol oxidase is denatured by alkaline condition/ high pH; [1] 1c It acts as a control to show that the colour change is due to the presence of polyphenol oxidase; [1] 1d Any 2 of Temperature, concentration of phenol/polyphenol oxidase solutions, volume of solutions, duration of experiment [2] 2a More than one raisin was used to find average results to ensure reliability/ consistency of results; [1] 2b 12.8-8.0= 4.8 cm3 Percentage increase = 4.8/ 8 x 100% = 60% [1] [1] 2c The concentration of cell sap in cells of the raisin was the same as in 10% sugar solution/ the water potential of cell sap in cells was the same as in the 10% sugar solution; There was no net movement of water molecules in or out of the raisin; [1] [1] 3a A: aorta; B: pulmonary artery; [1] [1] 3b Blockage of coronary arteries reduces the supply of oxygen and glucose to the heart muscles for respiration; The heart muscles would contract with lesser force/ heart pumps blood less powerfully around the body/ heart muscles die, leading to heart attack; [1] [1] 3c If X was blocked, more parts of the heart muscles would have less oxygen and glucose than if Y was blocked; [1] 3d There would not be issues with tissue rejection/ it is a less risky operation than removing the heart and replacing it with a new heart; [1] 3e Any 2 [2]

Qn Marking Scheme Remarks Marks Have a diet low in cholesterol and saturated fats, exercise regularly, manage low stress levels, do not smoke; 4a Glucose + oxygen  carbon dioxide + water [1] 4b 20 [1] 4c From 20 min to 40 min, the oxygen concentration decreased, causing an increase in anaerobic respiration; Lactic acid is a product of anaerobic respiration and the lactic acid concentration increases more the lower the oxygen concentration; OR Increased lactic acid concentration means more anaerobic respiration has taken place; Increased anaerobic respiration is a result of a decreased concentration of oxygen to carry out aerobic respiration; [1] [1] 4d 1. Lactic acid