CHIJ 2025 Sec 4 Bio Prelim MS P1 and P2

CHIJ Secondary School Preliminary Examination 2025 SUBJECT: BIOLOGY (6093) LEVEL: SECONDARY FOUR Mark scheme Paper 1 1 B 11 D 21 D 31 B 2 A 12 B 22 B 32 B 3 A 13 D 23 A 33 C 4 C 14 C 24 A 34 A 5 B 15 B 25 A 35 C 6 B 16 D 26 C 36 C 7 C 17 A 27 A 37 B 8 A 18 A 28 C 38 A 9 D 19 C 29 C 39 A 10 C 20 C 30 A 40 C Paper 2 Section A Answers Marks Markers’ comments 1 a Walls are thick and muscular ; 1 b N 1 c (from capillaries in lungs) to K, pulmonary vein ; back to B, left atrium, and then C, left ventricle of heart ; Through P, aorta ; To L, the renal artery, to reach the left kidney ; 1 1 1 1 d M has blood that has less urea (and excretory products) compared to L ; L brings blood to kidney, kidney removes urea from blood, that travels out through M ; 1 1 e the buildup of plaque causes the narrowing of coronary arteries + reduces blood flow to the heart muscles / less oxygen and nutrients to muscle ; causing muscle cells to die / unable to contract as much / inconsistent contraction / AOWTTE ; 1 1 Total 10

2 a Antibiotic T killed most of the bacteria in plate 4 ; 1 b Bacteria that were transferred from plate 3 and 4 were resistant to the antibiotics S and T respectively ; those resistant bacteria were incubated and multiplied / reproduced / underwent cell division, in plates 5 and 6 with the antibiotics, all bacteria there were resistant ; 1 1 c Any 1 answer: Do not misuse antibiotics ; Do not overuse antibiotics ; Complete all prescriptions of antibiotics Max 1 d Viral gastroenteritis is caused by a virus, viruses are unaffected by antibiotics / antibiotics only kill bacteria ; as viruses do not have cell structures that are targeted by antibiotics like cell wall, ribosomes, etc ; 1 1 Total 6 3 a 6H2O + 6CO2 –(light energy , chlorophyll)→ C6H12O6 + 6O2 1 b Cell X is a (palisade) mesophyll cell ; has many chloroplasts (that contain chlorophyll); allows for maximum light absorption for high rate of photosynthesis ; OR Cells are tall / long / elongated / cylindrical ; Allows them to be tightly packed to absorb more light to maximise rate of photosynthesis ; 1 1 1 c due to cooler temperatures in the evening, rate of water loss / transpiration decreases ; rate of water uptake / absorption by root hair cells exceeds rate of water loss ; cells regain turgidity / become firm again ; 1 1 1 d Do not agree Leaf hairs cause water vapour to accumulate outside of the stomata / traps water vapour / increases the humidity outside the leaf ; Concentration gradient between the intercellular air spaces and the outside of the stomata is less steep ; - 1 1 1

Rate of diffusion of water vapour out of stomata decreases with leaf hair, thus should not cut off the leaf hair ; Total 10 4 a Counting of numbers do not take into consideration the size / mass of each individual organism ; OR Pyramid of biomass is a better measure / representation of the amount of energy available ; 1 b Correct shape of pyramid (large at bottom, progressively smaller) ; Labelled correctly with producers at bottom, followed by primary consumers, secondary consumers, tertiary consumers ; 1 1 ci energy is made available when turtles consume other organisms / during feeding ; energy may be converted to form new cells / for protoplasm / form proteins / used in growth and repair of new cells ; 1 1 cii Total energy for decomposers = 1065 + 53 + 482 ; = 1600 kJ per year ; 1 1 d (micro)plastics are non-biodegradable and cannot be excreted ; thus when they are found in the ocean water and ingested into the marine organisms, (they accumulate in fatty tissue and) increase in concentration over time via bioaccumulation ; because turtles consume multiple prey to obtain enough energy, the concentration of microplastics in their body is higher than in previous trophic levels due to bioamplification / biomagnification ; 1 1 1 Total 10 5 a Asexual reproduction ; No fusion of gametes / only one parent bacterial cell is involved ; 1 1 bi Length before cell division = 6.4 µm Length after cell division = 3.0 µm; Percentage decrease in length = (6.4 – 3.0) /6.4 * 100 ; = 53.1% (3sf) ; 1 1 1 bii There were cells less than 6 µm long that underwent cell division, e.g. 40 cells at 5.8 µm that underwent cell division ; 1 c Any 2: Max 2

restriction enzymes cut both (human) genes of interest and bacterial plasmids at specific sites ; producing sticky ends that allow complementary base pairing ; thus subsequently the gene will be able to bind to the bacterial plasmid / form the recombinant plasmid / ref. to insertion of gene into plasmid ; Total 8 6 a A gene is a segment of DNA that codes for a particular trait / polypeptide / protein, for e.g. the gene for feather colour in chickens ; while an allele is an alternative form of a gene e.g. the black or white alleles for the gene of feather colour ; 1 1 bi gametes B W B BB BW W BW WW Phenotypic ratio: 1 Black : 2 speckled : 1 white Number of speckled chicks = ½*24 = 12 1 1 bii Since expected ratios are based on probability / based on theory of inheritance ; Actual ratios or numbers may differ, especially when sample sizes are small ; 1 1 Total 6 7 a cross and self pollination ; (self) pollen grain transferred from the anther of a flower to the stigma of the same flower or different flower on the same plant ; (cross) pollen grain transferred from one plant to the stigma of a flower in another plant of the same species ; 1 1 1 b Higher chance of cross pollination ; (any 2 elaborations) offspring may inherit beneficial qualities from both parents ; greater genetic variation to increase offspring surviving changes in the environment ; more viable seeds produced that are capable of surviving longer before germination ; 1 2 c Pollen grain germinates in response to the sugary fluid produced by the stigma ; Pollen tube grows out and the male gamete enters the pollen tube ; 3

pollen tube secretes enzymes to digest the surrounding tissue of the stigma and style and grows down the style into the ovary ; pollen tube enters the ovule via the micropyle ; absorb sap and burst to release the male gamete ; Nucleus of the male gamete fuses with the nucleus of the ovum to form the zygote ; 5 to 6 points – 3 marks 4 to 3 points – 2 marks 1 to 2 points – 1 mark Total 9 8 (a) Scale Line of best fit Axes labelled with SI units Plot points accurately 1 1 1 1 (b) From day 0/1 to 12, the level of progesterone in the blood remains constant ; From day 12 to 22 the level of progesterone rose gradually to 19 nmol/L ; From day 22 to 28 the level of progesterone decreased quickly/rapidly/sharply from 19 nmol/L to 2 nmol/L ; 1 1 1 (c) Straight line for constant level of progesterone or line moving up for increasing level of progesterone ; 1 (d) Oestrogen ; cause uterine lining to repair and thicken ; high levels lead to ovulation ; 1 1 1 Total 11

Paper 2 Section B Answers Marks Markers’ comments 9 a one molecule of glycogen is made up of many molecules of glucose ; each glucose molecule can be used in (aerobic) respiration to release energy ; 1 1 bi Any 2 points: At exercise intensity levels of below 40 A.U., body uses higher percentage of energy from carbohydrate than from fat + 1 data point, e.g. at 10 A.U., 70% fat and 30% carbohydrate ; As exercise intensity levels increase above 40 A.U., body uses higher percentage of energy from fat