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 bo