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 at 3, hence 300 mg per cm3 in 3 as compared to 320 mg per cm3 in 1. • Selective reabsorption of water back into bloodstream at 3, causing urea concentration to increase from 30 mg per cm3 at 1 to 2000 mg per cm3 at 3 1 1 1 1 1 b • Drink A • It increases volume of urine • Increase in temperature results in more sweat produced to remove excess heat • More water loss in the form of sweat 1 1 1 1 5 a • Concentration of PCB increases up the food chain + QV • Concentration is much higher in larger organisms + QV • PCB is non-biodegradable and cannot be excreted, hence will accumulate in the body • Concentration of PCB increases along the food chain, resulting in biomagnification, top consumers having highest concentration of PCB 1 1 1 1 bi • 1985 to 1990 2 bii • Monitor populations • Controlling the type of net used / mesh size • Alternative sources of fish • Use of laws to monitor / restrict watch weight • No catch zones / protected areas • Use of fish farms • Closed fishing seasons Any 2

3 6 a • D, A, B, E, C, F 1 b • Meiosis during gamete production ensure gametes are haploid / only has half the number of chromosomes • So that during fertilisation, fusion of the haploid sex gametes will restore the diploid number 1 1 7 a • Mutations are found in DNA • Asexual reproduction produces offspring that are genetically identical, so any random mutation will be inherited • Sexual reproduction involves two parents and mutation may only occur in one of the parents • Meiosis does not produce genetically identical cells and hence mutation may only be in some of the gametes 1 1 1 1 B c • A has lowest sickle cell allele but medium number of babies born with sickle cell anaemia while B has the highest birth and highest sickle cell frequency • B supports the statement but A does not support the statement, hence there is no link between births and frequency • Higher frequency may be due to the effect of the population density 1 1 1 8 a • Voluntary 1

4 bi 2 bii • 1st swimmer from both teams slower / longer reaction time + QV • Mean reaction times for swimmers 2-4 similar + QV 1 1 c • Nervous system is faster / hormones slower • Use of nerve impulses via neurones is faster than transport of hormones by blood • Allows faster response to escape from danger 1 1 1 9 a • Mutation leads to variation where some bacteria is more resistant to antibiotics • Antibiotics kill bacteria that do not have the mutation / not resistant • Bacteria who are more resistant have the selective advantage and will not be killed by the antibiotics • Resistant bacteria will survive, reproduce and pass the resistant gene to the next generation • Bacteria can be transmitted from one person to another through + descibre one method 1 1 1 1 1 b • Reduce misuse of bacteria / do not use for viral infectio • Ensure people complete the course of antibiotics • Prescribe / use antibiotics only when necessary / use less often • Develop new antibiotics • Use a combination of antibiotics • Rotate antibiotics Any 3

5 • Isolate patients with antibiotic resistant infections c • Antibiotics act on bacterial cell walls but viruses do not have cell walls • Antibiotics break up cell membrane but viruses do not have cell membrane • Antibiotics act on ribosomes, inhibiting protein synthesis but viruses do have ribosomes 1 1 1 10 ai • Sticky ends 1 aii • Isolate cry gene with restriction enzyme to produce sticky ends • Cut plasmid DNA with same restriction enzyme to produce complementary sticky ends • Mix cry gene and plasmid, use DNA ligase to seal plasmid with cry gene to form a recombinant plasmid 1 1 1 b • Cry gene contains amino acid sequence / base sequence which be be transcibed to form mRNA in nucleus • mRNA moves to cytoplasm and attaches to ribomsome • mRNA will be translated at ribosome to form polypeptide / protein 1 1 1 c • Mutation will elad to variations where there are caterpillars who are resistant to cry gene and those who are not • Those who are resistant has the selective advantage and will not be killed while those not resistant will die • The resistant caterpillar will survive, reproduce and pass the resistant gene to the subsequent generations 2

6 9 a • Line (L) – line/curve accepted + identify chitinase/most human either by labelling or including a key; • Axes (A) – labelled and correct orientation + all interval labelled; • Scale (S) – occupy at least 70% of grid + no ODD scale (1.5 box etc) • Points – all plotted correctly 4 b • Based on student’s graph; 1 c • Some of the enzyme are starting to denature and can no longer bind to substrate 1 d • Higher optimal temperature for chitinase than most human enzyme + QV • Higher activity for most human enzyme at 25 oC; • Some enzymes are still functioning at high temperature (70-80 oC); + QV Any 2 points OR any valid points stated; 2 e • Breaks down dead organic matter and return the nutrients to be used by ot