GMSS 2024 P2 MS ANS

2024 Sec 4 Express Biology Prelim (6093) Marking Scheme Paper 1 1 2 3 4 5 6 7 8 9 10 B B B D A A C C B C 11 12 13 14 15 16 17 18 19 20 C D D A D B B C D B 21 22 23 24 25 26 27 28 29 30 A A A C B C C C D B 31 32 33 34 35 36 37 38 39 40 A C D A C D B D C C Paper 2 Section A 1 a Accept any of nucleus (N), cytoplasm (C) or cell membrane (CM) 1 b i • Circular muscles contract and relax in a rhythmic wave-like motion to push food down the small instestine; 1 b ii • More mitochondria allow more energy to be release via higher rate of aerobic respiration; 1 c • Any organs with circular muscles; e.g Stomach OR oesphagus OR large intestine OR Eye OR rectum R: small intestine, duodenum, jejunum 1 d i • Red blood cell OR muscle cells OR any acceptable answers R: root hair cell 1 Red blood cell: • Contain haemoglobin to carry oxygen molecules; • Lack nucleus to allow more volume/space to contain haemoglobin; • Circular biconcave shape to allow larger surface: volume ratio; • Flexible and able to squeeze through blood capillaries OR 2 N C CM

2 Muscle cell: • Has many mitochondria to generate energy through aerobic respiration; • Has many nucleic to increase protein sysnthesis; Any acceptable specialised cells like nerve, liver, heart, etc are accepted with correct adaptations 2 a Carbohydrate: • Immediate source or energy OR energy storage as glycogen; Fats: • Energy storage; • Insulation (of heat) • Protection of vital organs against physical injury; • Main component of membrane; Any 2 points, one from each carbohydrate and fats. 2 b • Mix a portion of the man’s meal with water and decant; • Using 2 cm3 of the decanted solution, add 2 cm3 of biuret solution and mix • If protein is present, mixture will turn violet otherwise mixture will remain blue; 3 c i • Person may not have enough insulin in his body; • To stimulate liver to convert the excess glucose to store as glycogen; 2 c ii • Insulin can be digested by enzymes/protease OR insulin structure affected by pH. R: insulin cannot be absorbed 1 3 a All labelled correctly - 2 marks, Any 1or 2 labelled correctly – 1 mark 2 b • Blood circulates heart twice via pulmonary circulation and the systemic circulation; • In pulmonary circulation, deoxygenated blood is carried from heart to lungs to be oxygenated and then back to the heart; • In systemic circulation, oxygenated blood is pumped from the heart to the rest of the body and deoxygenated blood is carried back to the heart; Any 2 points 2 c i • Coronary arteries 1 P Q R

3 ii • Heart tissue/cells will receive less oxygen and glucose and will • Less respiration occurring, releasing less energy, cells die and person may suffer heart attack; 2 iii • Either: smoking OR age OR sedentary lifestyle OR genetics OR unhealthy diet; Any 2 of the above. 2 4 a • Aerobic respiration (R: respiration) 1 b i • At 20th minute 1 b ii • 2% 1 c • Decreasing oxygen level in the seal’s body will reduce the rate of aerobic respiration; • Seal muscle cells will start to undergo anaerobic respiration; 2 c • Lactic acid amount will decrease; • Lactic acid is sent to the seal’s liver to be converted to glucose; 2 5 a • High temperature / heat stimulate the receptors to generate nerve impulses sent to the spinal cord by sensory neruone, Z • Sensory neurons transmit nerve impulse to relay neurone, Y via a chemical synapse and from relay neurone to motor neurone, X via another chemical synapse • Motor neurons transmit nerve impulse to effect, the muscles which will contract to withdraw the hand from the hot object. 3 b • Person will still be able to feel the heat but will not be able to move hand away immediately/involuntarily/via reflex • Sensory neurone is able to transmit nerve impulse to spinal cord for it to be transmitted to brain to sense the pain 2 c Similarity: • Both the nervous and hormonal systems play crucial roles in regulate functions such • maintain homeostasis; • Respond to sitmuls; Differences (nervous vs hormonal): • Relatively fast vs slow; • Short lived vs long lived; • Transported by neurone vs blood; • Nerve impulses vs hormone; • Usually localised vs usually more than one target organ; • Can be voluntary/involuntary vs definitely involuntary; One answer from similarity and one answer from any of the differences. 2 6 a • K: burning OR combustion (of fossil fuels); • L: respiration; • M: photosynthesis; 3 b • Ocean OR any acceptable source of carbon sink 1

4 c • Burning of fossil fuel leads to increase in carbon dioxide level; • The accumulation of greenhouse gases in the atmosphere traps more heat and leading to an increase in global temperatures/global warming 2 (d) • Prevent extinction AND • Prevent disruption to carbon cycles • e.g of preventing greenhouse gases from increasing (CO2 or otherwise is accepted) R: population control (food chain/web) or any non biodiversity/ecosystem related answers. 7 a • Restriction enzyme; 1 b i • Both the plasmid vector and the gene of interest/target gene are treated with the same restriction enzyme(s) to form complementary sticky ends • DNA ligase is used to seal up the plasmid with the gene of interest/target gene; R: ligase 2 b ii • Recombinant plasmid are introduced into cotton plant cells via heat/electrical shock; • Cotton plants with recombinant plasmid are transformed and will produce the toxic protein; 2 c • New protein in GM food might cause allergy; • GM plant seeds cannot germinate; • Animals are used in research; • Possible biological warfare; • Antibiotic resistant bacteria; • Selective individuals having the benefits; R: religious, safety, personal concerns 2 8 a • Abnormal cilia cannot move mucus containing pathogens from the respiratory tract; • Pathogens (examples accepted) in the mucus multiply and cause infection in the respiratory tract; 2 b • Dd; • Individual 13/child of 6 is affected/homozygous recessive, would have inherited one recessive allele from 6. Since 6 is normal, 6 must have one dominant allele. OR • Individual 1 / parent of 6 is homozygous recessive, would have passed the recessive allele to 6 2 c i • Genotype of parents: Dd x Dd; • Gametes: D, d, D, d (all circled); • Genotype of offspring: DD, Dd, Dd, Dd; • Phenotype of offspring: Normal, carrier, affected; 3 marks for all rows correct, 2 marks for three rows corrow, 1 mark for one/two rows correct; 3 c ii • Probability of child getting PCD = ¼ OR 25% • Probability of child being female = ½ OR 50% 2

5 • Hence probability of child being female with PCD = ½ x ¼ = 1/8 OR 12.5% OR 0.125 NO ECF if ci answers are wrong. c iii • Having PCD does not cause individual to die, can still give rise to offsprings having the recessive allele for PCD; OR exist as carriers to pass on the allele; 1

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 other organisms (example plants); • carbon dioxide is released during the breaking down of dead matter and returned to the atmosphere; 2 temperature / oC relative enzyme activity / % x x 30 35 40 45 50 55 60 65 70 0 20 40 60 80 100 x x x o o o o o chitinase most human

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