CGS 2024 P2 MS ANS

1 CGS 2024 Biology Prelim Paper 2 Answers Qn Answer Key Section A 1a • high temperature denatures the enzymes • (Few hours before) allows sufficient time for enzymes to work on the proteins in the meat / more proteins to be broken down 1 1 1b • Pepsin, digest / break down proteins into polypeptides 1 2ai 750 / 5800 X 100% = 12.931 = 13% (nearest whole number) 1 1 2aii Coronary artery 1 2aiii 600 2b • Cardiac / skeletal muscle • More oxygen and glucose supplied for higher rate of respiration to release more energy OR • To remove lactic acid / carbon dioxide at a faster rate • skin • allow more heat to be lost to the surrounding 1 1 1 1 2c • less blood + QV , is transported to the digestive organs • less / slower digestion / absorption of digested food products 1 1 3b • ventricular diastole is occurring / left ventricles are relaxing • when pressure of left ventricle is less than the pressure of left atrium • bicuspid valves are opened 1 1 1 4a Both have muscle/elastic tissues / valves 1 4b C F Has RBC/WBC/platelets/plasma No RBC/WBC/platelets/plasma Has proteins/antibodies/amino acids/glucose/fats No proteins/antibodies/amino acids/fats/glucose Lower urea concentration Higher urea concentration 1 1 1 4c C Dialysis fluid Has RBC/WBC/platelets/plasma/ antibodies / urea No RBC/WBC/platelets/plasma / antibodies / urea 1 5a Respiration : glucose Growth : amino acids / proteins 1 1 5b • add pH buffer for optimum pH OR • place / incubate at optimum temperature • to speed up the rate of enzyme reaction 1 1 5ci H 1

2 Qn Answer Key 5cii • bacteria • antibiotics are effective against / kills bacteria 1 1 5d • bacteria is of different variety • some bacteria are more resistant to bacteria • patients did not complete course, resulting in more resistant bacteria surviving and reproducing 1 1 1 6ai • root hair cell 1 6aii • solvent for transport • maintains turgidity of cells / keep leaf upright • medium for enzyme action any 2 1 1 1 6c • photosynthesis • transpiration / replace thin film of moisture on mesophyll cells 1 1 6d • rate of water loss is greater than rate of water uptake / rate of transpiration is greater than rate of water absorption • cell loses turgidity / wilting occurs 1 1 7b • 90% of the energy is lost as heat via respiration / uneaten body parts / egested waste / excreted waste 1 7c • Washed into the lake by rain and absorbed by the water plants • Organochlorides are non-biodegradable and cannot be excreted, will accumulate / become concentrated in the fatty tissues of organisms • As it passes along the food chain, it increases in concentration along the trophic level and become most concentrated at the highest trophic level 1 1 1 7d • Nitrates / phosphates washed into the lake promotes the growth of algae, leading to eutrophication • Algae will block sunlight from reaching the underwater plants, which will die as they cannot undergo photosynthesis • Decomposers/bacteria will multiply in numbers, using up the oxygen in the water, causing the fish to die due to lack of oxygen 1 1 1 7e • Breaks down dead plants and animals • Into simpler compounds like carbon dioxide that can be released into the atmosphere 1 1 8b • Phenotype is independent of gender • Not related to age • There are more people with free earlobes than attached earlobes • This is discontinuous variation Any 2 1 1 1 1 8c • (43+44) / (13+15) = 3.107 • Ratio is 3 free earlobe : 1 attached earlobe 1 1 8d • Monohybrid inheritance • Parents are heterozygous, allele for free earlobe is dominant 1 1 9a • Chemical substance, produced in minute amount by endocrine gland • Carried by blood 1 1

3 Qn Answer Key • To exert its effects on one or more target organs 1 9b • Chemical molecules diffuses through the epidermis of skin into blood capillaries • Transported by plasms in the vein to the right atrium via the vena cava • And to the right ventricle, to the lungs and back to the left atrium, followed by left ventricles • And out of the heart via aorta to the artery that leads to the tongue 1 1 1 1 9c • Receptors in the tongue are stimulated to generate nerve impulses • Transmitted by sensory neruone to the brain • Brain will interpret the taste 1 1 1 10a • Diaphragm contracts and flattens • External intercostal muscles contract and internal intercostal muscles relax • Ribcage moves upwards and outwards, increasing volume of thoracic cavity • Pressure of atmospheric air is higher than pressure in lungs, causing air to rush in • At the alveoli, oxygen dissolves in the thin film of moisture lining the surface of the alveoli before diffusing through into the plasma and into red blood cell • Heart will pump blood containing oxygen to the liver where oxygen will diffuse from red blood cell into the tissue fluid and into the liver cell 1 1 1 1 1 1 10b • When blood glucose level is below normal, more glucagon will be secreted by pancreas to be sent to the liver • Glucagon will stimulate liver cells to convert stored glycogen to glucose • Glucose is broken down during aerobic respiration to produce carbon dioxide and water 1 1 1 11a • During day time, concentration of carbon dioxide is higher in the air than in the intercellular air space • Carbon dioxide molecules diffuses through the stomata and into the intercellular air spaces • Carbon dioxide dissolves in the thin film of moisture lining the mesophyll cells before diffusing into mesophyll cells • Carbon dioxide will diffuse into the chloroplasts of mesophyll cells • During photosynthesis, light energy will be absorbed by chlorophyll and converted to chemical energy • Carbon dioxide will react with water to form glucose • Excess glucose formed will be converted to starch and stored in leaf 1 1 1 1 1 1 1 11b • Starch in leaf is broken down to form glucose • Glucose reacts with fructose to form sucrose which is transported / translocated by phloem to the roots • Sucrose is converted back to glucose and excess glucose is converted to starch for storage 1 1 1