CCHY 2018 Bio Yearly TYS ANS

6093 Biology Yearly TYS 2018 No Paper 1 Marks Remarks 1 C 1 2 A 1 3 B 1 4 B 1 5 C 1 6 D 1 7 C 1 8 A 1 9 B 1 10 A 1 11 C 1 12 B 1 13 C 1 14 D 1 15 A 1 16 B 1 17 C 1 18 C 1 19 B 1 20 D 1 21 B 1 22 D 1 23 A 1 24 D 1 25 C 1 26 C 1 27 D 1 28 B 1 29 B 1 30 A 1 31 C 1 32 D 1 33 A 1 34 C 1 35 D 1 36 A 1 37 C 1 38 B 1 39 D 1 40 D 1 Total 40

Paper 2 Section A Marks Remarks 1ai chromatid 1 1aii stage 3: metaphase stage 4: anaphase 1 1 1bi 2 1 1bii plant 1: AA plant 3: aa 1 Total 5 2ai regulation of blood glucose concentration/ deamination of excess amino acids into ammonia and then urea/ breakdown of haemoglobin and stores iron released/ detoxification of alcohol by alcohol dehydrogenase into acetaldehyde/ production of bile used for emulsification of fats 3 2aii C 1 2aiii name: bile; function: emulsify fats into smaller fat droplets to increase surface area to volume ratio for faster digestion of fats by lipase; 1 1 2bi 40 °C 1 2bii rennin has denatured at high temperatures of 60 °C beyond optimum temperature + active site is altered + substrate is unable to bind to enzyme to form e nzyme- substrate complex; 1 2c solid lumps remains in the stomach longer compared to liquid milk; allows complete digestion and greater absorption of nutrients; 1 1 Total 10

3ai 3 minute 1 3aii as temperature increases from 15 °C to 21 °C, clotting time decreases rapidly from 24 min (longest time taken) to 10 min; as temperature increases further to 35 °C, clotting time continue to decreases gradually to 2.5 min + lowest time taken for clotting/ as temperature increases from 15 °C to 35 °C, clotting time decreases from 24 min to 2.5 min; rate of clotting increases when temperature increases; 1 1 R: no quotation of data 3b prevents foreign particles from entering the bloodstream; prevent excessive loss of blood; 1 1 Total 5

4a S: walls of alveoli are richly supplied with blood capillaries + F: continuous flow of blood maintains a steep concentration gradient for faster diffusion of gases; S: thin film of moisture covers the inner surface of the alveolus + F: dissolve gases for faster diffusion; S: walls of alveoli are one-cell thick + F: provides short diffusion distance for faster diffusion of gases; S: numerous alveoli in the lungs + F: provide large surface area to volume ratio to increase rate of diffusion of gases; 3 structure + function 4b lower levels of carbonic anhydrase to catalyse the reaction between carbon dioxide and water in RBCs + forming lower amounts of carbonic acid; decrease amount of carbon dioxide converted to hydrogencarbonate ions for transport in the blood plasma; lower rate of carbon dioxide being transported to the lungs for excretion + leads to carbon dioxide poisoning/ excess carbon dioxide in the RBC/ slower gaseous exchange; 1 1 1 R: no relating to context 4ci pressure decreases from 0 a.u. to -1 a.u. in the first second + reaches the lowest point at -1 a.u.; pressure increase from -1 a.u. to 0 a.u. in the next second; 1 1 1st second next second 4cii muscles of diaphragm contract + diaphragm flattens + external intercostal muscles contract while internal intercostal muscles relax; moving the ribs upwards and outwards + sternum moves up and forward causing lungs to expand + increasing thoracic volume; lowering air pressure in the lungs/ atmospheric pressure is higher than pressure in the lungs + forces atmospheric air into lungs; 1 1 1 diaphragm + ICM ribs + sternum + volume pressure + air enters Total 11

5ai 173.5 1 R: unit written 5aii 52.0 − 20.8 52.0 × 100% = 60% 180.0 − 175.5 180.0 × 100% = 2.5% 1 5aiii urea 1 5b structure A is the glomerulus + Stucture B is the venule; ultrafiltration + high hydrostatic blood pressure in A forces small molecules i.e. glucose, amino acids, mineral salts and nitrogenous waste products to pass through the partially permeable basement membrane into the Bowman’s capsule + blood cells, platelets and large molecules i.e. proteins and fats are retained in the glomerular capillaries; blood capillaries surrounding the nephron unites to form B + join to form a bra nch of renal vein + carries deoxygenated blood with lower concentration of mineral salts and nitrogenous waste products and more carbon dioixide than blood entering the kidneys; 1 1 1 Identify both structures Function of A Function of B Total 6 6a A is main vein/ vein/ mid-rib + contains xylem and phloem situated close to mesophyll cells; xylem transports water and dissolved mineral salts from roots to mesophyll cells by transpiration pull + phloem transports sucrose from the leaves to other parts of the plant by active transport; 1 1 Identify structure and tissues Functions of tissues 6bi sucrose 1 6bii phloem tissue 1 6biii 65𝑐𝑚 2.5ℎ = 26 𝑐𝑚/ℎ 1 1 Total 6

7a aerobic respiration (P) in animal and plant cells + combustion (S) or burning of fossil fuels produces carbon dioxide + returning carbon dioxide to the environment; photosynthesis (Q) in plants absorbs carbon dioxide to be used to synthesise glucose + removing carbon dioxide from the environment; nutrient cycling + constant removal of carbon dioxide from environment and returning of carbon dioxide into the environment + ensures that concentration of carbon dioxide in the environment is relatively constant; 1 1 1 Return CO2 Remove CO2 Nutrient cycling 7b bacteria and fungi are decomposers that break down dead organisms/ dead organic matter; decomposition and respiration of bacteria and fungi releases carbon dioxide into the environment; dead decomposed bodies of organism buried in the Earth for millions of years will produce fossil fuels such as coal, natural gas and oil + used in combustion releasing carbon dioxide to the environment; 1 1 1 Total 6

Section B 8ai All points plotted correctly; Best fit line + smooth curve; Correct orientation; Correct axes + equal intervals; 4 8aii 100 − 15 = 85 𝑎. 𝑢. 1 R: wrong units 8aiii sensitivity increases from 5 a.u. to 100 a.u. as wavelength increases from 420 nm to 500 nm + highest sensitivity of 100 a.u. when wavelength is at 500 nm; as wavelength i ncreases further from 500 nm to 6 00 nm, sensitivity decreases from 100 a.u. to 5 a.u. + lowest sensitivity of 5 a.u. at 420 nm and 600 nm; 1 1 8aiv 72 a.u. 1 8b photoreceptor in retina stimulated by bright light + nerve impulses produced; nerve impulses travel along sensory neurone in optic nerve to relay neuron in the brain + to the motor neurone and reaches effector (muscles of the iris); circular muscles of the iris contract + radial muscles of the iris relax + pupil constricts + reducing light entering the eye; 1 1 1 Total 11 0 20 40 60 80 100 120 420 440 460 480 500 520 540 560 580 600 sensitivity of retina/ a.u. wavelength of light/ nm Graph of Sensitivity of Retina against Wavelength of Light

9a Diffusion is the net movement of molecules down concentration gradient but osmosis is the net movement of water molecules down water potential gradient; Diffusion and osmosis does not require energy but active transport requires energy; Diffusion and osmosis are movements down a concentration and water potential gradient respectively but active transport is a movement against a concentration gradient; 1 1 1 D & O DO & AT DO & AT R: mere definition 9bi Water molecules enter cell B down water potential gradient through the partially permeable cell membrane + vacuole expands and pushes against t