Mayflower 2019 Bio Prelim P2 MS

1 Answer Key (Prelim 2019 – 6093/02) Paper 2 Section A: Answer all questions [50 marks] 1(a)(i)Transpiration is the loss of water vapour from the aerial parts of the plants through the stomata of the leaves. [1m] (a)(ii)xTemperature As the temperature during the drought is very high, there will be an increase in the rate of evaporation of water from the surfaces of the leaf. This increases the rate of transpiration. xHumidity As the humidity is very low, the water vapour concentration gradient between the surrounding air and the intercellular air space (in the leaf) is very high. Water vapour diffuses out of the leaf increasing the rate of transpiration. (light intensity and wind speed not accepted) [2m] [2m] (a)(iii)xWilting will cause the leaves to droop/fold up, reducing the surface area exposed to sunlight. xStomata size reduced xThis helps the plant to reduce transpiration as the guard cells turn flaccid. [2m] (b) Photosynthesis [1m] (c) xFrom 1800 to 2000 hours, the uptake of oxygen is increasing as the rate of respiration in the plant is now higher xthan the rate of photosynthesis as the light intensity of the surrounding decreases to zero at night. [2m] Total: 10 2(a)(i)5m i n u t e s [1m] (a)(ii)Anaerobic respiration [1m] (a)(iii)xAerobic respiration is not able to meet the energy demands of the athlete. Muscles will respire aerobically and anaerobically to get more energy creating an oxygen debt. xAnaerobic respiration releases a lactic acidas a by-product. xThe lactic acid produced caused the pH to decrease from 7.6 to 6.2 from 5 min to 20 min. [3m] (b) glucose + oxygen ĺ carbon dioxide + water + large amounts of energy [1m] (c)(i)xThe oxygen enters the alveoli where it dissolves into the thin film of moisture lining the inner walls of the alveoli increasing the speed of diffusion. xThe walls of the alveoli are one-cell thickwhich allows for rapid diffusion of dissolved oxygen into the red blood cells. 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2 (c)(ii)xTar will paralyse the cilia causing a build-up of mucus which may result in bronchitis / frequent coughing. xThe frequent coughing may cause emphysema where the walls of the alveoli are damaged reducing the surface area for gaseous exchange. [2m] Total: 10 3(a)(i)A–A o r t a B – Pulmonary vein [2m] (a)(ii)Deoxygenated and oxygenated returns to the right and left atrium from the body and lungs respectively. xDuring atrial systole, the higher pressure in the atriums compared to the ventricles causes the atrio-ventricular valves to open forcing blood into the ventricles. xDuring ventricular systole, the higher pressure in the ventricles compared to the atrium and arteries causes the semi-lunar valves to open and the atrio-ventricular valves to close creating the “lub” sound. xAs the blood is pumped to the lungs and rest of the body, the higher pressure of the aorta and pulmonary arterywill cause the semi-lunar valves to close to prevent backflow of blood. This will create the softer “dub” sound. (1m awarded for stating when the “lub” and “dub” sound is produced) [1m] [1m] [1m] [1m] (a)(iii)xThe hole in the median septum will cause the oxygenated blood in the left side of the heart to mix with the deoxygenated blood in the right side of the heart. xThis will result in less oxygen transported in the blood around the body. Hence, he will be unable to participate in any strenuous activities. [2m] (b