PLMGS 2024 P2 MS ANS

PLMSG 2024 Sec 4 Express Biology Prelim (6093) Marking Scheme Paper 2 Section A 1 a • 1, 5, 2, 4 Every 2 correct = 1m 2 b i • J receives blood from left ventricle that has a thicker muscular wall, generating a higher pressure • M receives blood from right ventricle, has a less thick muscular wall 1 1 b ii • Presence of a larger lumen, reducing pressure • Blood in K and L travelled through capillaries 1 1 2a A • Microvilli • Increase surface area to volume ratio for faster absorption of digested food molecules B • Mitochondrion • Undergoes aerobic respiration to release energy for active transport of digested food molecules 1 1 1 1 • Toxin causes more chloride to be released into the small intestine • Water potential in small intestine is lower than in blood • Net movement of water molecules from blood into small intestine by osmosis 1 1 1 c(i) • An agent that resembles pathogen, preventing infectious diseases by stimulating white blood cells to produce antibodies quickly. 1 c(ii) • More pathogens . diarrhoea/fever in non-vaccinated group + QV • Some vaccinated people did get symptoms so vaccine is not 100% effective + QV 1 1 3 ai • Increase in temperature increases the K.E of molecules involved in photosynthesis • More effective collision between enzyme and substrate molecules, more E-S complex formed. • Increasing the rate of diffusion of carbon dioxide into leaves, more carbon dioxide available for photosynthesis. • Increases rate of transpiration, more water can be supplied to the leaves for photosynthesis 1 1 1 1 aii • Lower concertation of water vapour in the air / steep water vapour concentration gradient between air and intercellular air spaces • Increased diffusion of water vapour of of leaf via stomata • Stomata closes when rate of water loss / transpiration is higher than rate of water absorbed,less carbon dioxide can enter. 1 1 1

2 aiii • Record the difference in concentration of carbon dioxide between air in and out / chamber 1 and 3 / before and after • Divide by time / 15 min 1 1 b ii • Carbon dioxide uptake at 35ºC is 90 ug per hour per cm2 of leaf which is less than carbon dioxide used in leaf • Carbon dioxide is produced by cells during aerobic respiration • Carbon dioxide released by cells also used for photosynthesis 1 1 1 biii • Reduces extraction of non-renewable fuels • Temporary removes carbon dioxide • Does not cause further increase in greenhouse effect / global warming • It is a sustainable process 1 1 1 1 4 a • Ultrafiltration occurs at Bowman’s capsule, region 1, where small molecules like glucose, urea and salts are forced out of blood plasma into 1 • Protein molecules are too large to pass through the partially permeable membrane, hence 0 mg per cm3 at 1 • At region 3, loop of Henle, all glucose have been selective reabsorbed back into the bloodstream by active transport, hence 0 mg per cm3 of glucose at region 3 • Selective reabsorption of some salts back into the bloodstream