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 concentration will decrease; 2. The rate of breathing will be high so that more oxygen can be taken in/ increase heart rate/ blood flow to muscles; 3. Oxygen is used to break down lactic acid into carbon dioxide and water; Cannot just mention pay off oxygen debt [1] [1] [1] 5ai Difference= 138-122 = 16 Percentage difference = 16/138 x 100 = 11.6% [2] 5aii Any 2 Glucose does not need to be digested, but starch needs to be digested; Glucose is absorbed into the bloodstream faster/ immediately; Glucose absorption from starch continues for a longer time as it takes time for digestion before absorption can take place; [2] 5b Insulin is released in response to increased blood glucose concentrations; As such, after eating glucose, there will be a greater increase in insulin concentration at 30 min (8.7) than after eating rice (4.4); Insulin increased faster when glucose was consumed as blood glucose concentration increased faster than when starch was consumed Must quote some data from graph for full award of 3 marks [1] [1] [1] 5c 1. Insulin stimulates liver to convert excess glucose to glycogen; 2. Glycogen is stored in liver cells; 3. Insulin also increases uptake of glucose by cells and increases tissue respiration; [1] [1] [1] 6a Increasing light intensity increases the rate of photosynthesis; R: reverse argument [1] 6b Carbon dioxide concentration a limiting factor; Carbon dioxide is a raw material needed for photosynthesis; [1] [1] 6c 1. Due to insufficient water in leaves as water is a raw material needed for photosynthesis; 2. stomata close and less carbon dioxide would be taken into the leaves to be used for photosynthesis; 3. drooping leaf position decreases the amount of light energy absorbed for photosynthesis; [1] [1] [1] 7a Any set of The blood capillaries have one-cell thick walls/ tiny pores in the membranes; to speed up the process of ultrafiltration; OR The blood capillaries have a thin partially permeable membrane; [2]

Qn Marking Scheme Remarks Marks that allows only small soluble molecules or ions to pass through; 7bi Label Bowman’s capsule G; [1] 7bii There is a decrease in the concentration of glucose as all the glucose is reabsorbed back into the blood stream; There is a decrease in the concentration of sodium chloride as some mineral salts are reabsorbed back into the blood stream; Urea concentration increases in urine as it is not reabsorbed back into the blood stream; [1] [1] [1] 7biii After consuming a meal rich in meat, there would be increased amino acids in the bloodstream; Excess amino acids would be deaminated in the liver to form more urea; In glomerular filtrate, there would be a higher level of urea; [1] [1] [1] 8a Mitosis; Identical copies of original bacterium are produced at the end of stage M/ All copes have the same identical genetic material; All cells will have the ability to be able to produce the same insulin; [1] [1] [1] 8b Any 2 Advantages Yield of genetically modified crops is good/ plants can grow quickly; Able to grow in environmental extreme conditions/ new areas; Able to transfer beneficial genes or characteristics between species; Can be resistant to diseases or pests; Any 2 Dangers Risk of genetic spread to other species; Expensive and costly to do genetic engineering; Possible health risks to humans or other organisms when consuming genetically modified crops; [2] [2] 9a Number of people Blood Group - Clean, clear bars drawn/point plotted correctly; - Correct axis labels; - Appropriate scale with regular intervals; [1] [1] [1] 9b Discontinuous variation; There are a few clear-cut phenotypes/ genes do not show additive effect; [1] [1] 0 100 200 300 400 500 A AB B O

Qn Marking Scheme Remarks Marks 9ci Parent Phenotype blood group A blood group B Parent Genotype IAIO x IBIO Gamete IA IO IB IO Offspring Genotype IAIB IAIO IBIO IoIo Offspring Phenotype AB A B O Probability of child with blood type AB: 25%/ 1/4 [1] [1] [1] [1] 9cii B or O [1] 10a Bacterial cell as a cell wall, but an animal cell does not; Bacterial cell does not have the DNA or genetic material enclosed within a membrane, but an animal cell has a nucleus containing genetic material; [1] [1] 10b Any 3 Age group trend: more hospitalisations for group aged 75 (in 1998, around 110) and above/ 15-74 year olds (in 1998, less than 45), fewer hospitalisations; Those above 75 may have weaker immune system/ more prone to tuberculo