VS 2015 O Level Pure Biology P2 MS w Feedback

2015/ 5158 Biology Suggested Answer Scheme – P2 Qn No Answer Mark Feedback 1(a) A: starch B: maltose C: salivary amylase 1 1 1 Question states that this reaction takes place in the mouth. Note that the only chemical digestion that occurs in the mouth is the digestion of starch. 1(b)(i) Body temperature 1 1(b)(ii) pH 1 1(c) (BLOCKAGE) Lack of bile released into small intestines + As bile duct functions to transport bile from gall bladder to small intestines Bile functions to emulsify fats/break up fats globules into tiny fat droplets; (AFFECT) Lack of bile will reduce chemical digestion of fats into fatty acids and glycerol by lipase significantly + Due to reduced surface area to volume ratio of fats. 1 1 1 A clear understanding of the difference between physical digestion with chemical digestion was required. Break up (physical digestion VS break down (chemical digestion) Many recognised that lack of bile would slow down fat digestion, rather than prevent it altogether. 2(a) The process involving the fusion of two gametes, formed through meiosis, to form a zygote . To produce genetically dissimilar offspring. 1 1 1 Candidates were aware of the fusion of gametes and the production of zygote. Good responses described the production of genetically dissimilar offspring and made reference to meiosis.

2(b) (HOW) Pollen grain is spiky and highly patterned (ADAPTED) Allowing it to cling on the bodies of animals that visits the flower to obtain nectar (DISPERSAL) When the animal visits the next flower and brushes against the stigma + the pollen grain is deposited on the stigma 1 1 2(c)(i) Pollen tube 1 2(c)(ii) (describe)( explain) Tip of part A secretes digestive enzymes that break down the surrounding tissue of the stigma and style → allowing the tube to burrow through towards the ovule; pollen tube carrying the male nuclei enters the ovule through the micropyle Tip then absorbs sap and burst → r eleasing the male nuclei into ovule where the female nuclei are located. 1 1 1 3(a) 24˚C 1 3(b) 1. As the air temperature increases, the body temperature of the insect increases. 2. The insect body’s temperature is not maintained at a certain temperature – instead, it takes on the same temperature as the surroundings/environment 1 1

3(c) 2 3(d) When blood temperature increases above norm, the sweat gland becomes more active → More sweat is released onto the surface of skin; When water in sweat evaporates from the surface of skin → More latent heat of vaporisation is removed from the body Body temperature decreases back to norm → Sweat glands become less active 1 1 1 4(a) A: Aorta B: Pulmonary vein 1 1 4(b) C prevents backflow of blood from pulmonary artery to right ventricle during ventricular diastole 1 Some lacked precision in their response, which required c onsideration of the exact location of the valve . 4(c) Deoxygenated blood enters right atrium from vena cava during atrial diastole (DESCRIBE) when pressure of right ventricle falls below right atrium, tricuspid valve opens (E) and blood passively fills right Address both parts of the question – “describe” and “explain”

ventricle + right atrium actively fills right ventricle with blood during atrial systole; (EXPLAIN) ventricle contracts, shutting tricuspid valve (EXPLAIN) when ventricular pressure exceeds atrial pressure semi-lunar valve opens when ventricular pressure exceeds pressure in pulmonary artery (REACH THE LUNGS) blood leaves the heart forcefully through pulmonary artery and is transported to the lungs(DESCRIBE) 1 1 1 1 5(a) Insulin concentration decreases by 90 arbitrary units 1 5(b) Glucose is still in demand by cells for respiration; Since no glucose is absorbed into bloodstream at the small intestine during fasting; Less insulin is secreted to prevent the conversion of glucose into glycogen; Ensuring that blood glucose concentration does not decrease and is kept within norm 1 1 5(c) Exercise imposes stress on the body, triggering release of adrenaline into bloodstream; Increases heart rate and blood pressure to allow more blood to reach skeletal muscles quickly for increased respiration Increases rate of breathing/ ventilation to bring in more oxygen into the lungs, allowing more oxygen to diffuse into blood Raises blood glucose level by conversion of glycogen to 1 1 1 1

glucose, more respiratory substrates transported by blood 6(a)(i) I A I O 1 6(a)(ii) I B I O 1 6(a)(iii) Child 2: AB Child 4: O 1 1 6(b) I A and I B 1 Some examples of miswriting for this question: - I A I B (this shows genotype, not two separate alleles as asked for) - AB (this shows phenotype, not two separate alleles as asked for) 7(a)(i) An organism that is unable to make its own food and obtains energy and nutrients by feeding on other organisms 1 Some candidates repeated the term in their definition without showing they understood the meaning of that term 7(a)(ii) The position an organism occupies in a food chain 1 7(b)(i) plankton → small fish → large fish → fisherman 1 7(b)(ii) Plankton take in mercury compounds from seawater. Since mercury cannot be excreted, it is stored in plankton. Small fish feed on plankton, thereby transferring stored mercury into small fish. Each small fish would need to feed on many plankton to meet its energy needs. Concentration of mercury would consequently increase significantly, from 0.1 p.p.b in seawater to 200 p.p.b in the flesh of small fish. 1 1 1

8(a) 4 Ensure that x-axis : time of day (as stated in question stem) 8(b)(i) Difference: 0.32 – 0.014 = 0.306 percentage by volume 1 8(b)(ii) (D) Concentration of carbon dioxide increases steeply by 0.280 units to reach maximum at 6:00. From 6:00 – 8:00, concentration of carbon dioxide decreases by 0.294 units. Thereafter, the concentration of carbon dioxide drops by a mere 0.012 units to reach a minimum of 0.014 units at 14:00. 1 1

(Explain) Concentration of carbon dioxide increases drastically to maximum of 0.320 units at 6:00 due to excessive release of carbon dioxide from exhaust fumes of cars/tractors/small airplanes near the paddy field Light intensity is low, no photosynthesis occurred; Rate of carbon dioxide release from these sources and from respiration exceeds rate of carbon dioxide intake by photosynthesis in plants As the day progresses, light intensity increases; Plants photosynthesise, reducing carbon dioxide concentration as rate of photosynthesis exceeds rate of carbon dioxide release 1 1 8(b)(iii) Rate of photosynthesis in exceeds rate of respiration; Excess oxygen is released by plants into the air 1 9(a) Carbon monoxide Binds irreversibly with haemoglobin to form carboxyhaemoglobin Reduces carrying-capacity of oxygen in