2015 Pure Biology TYS Answers

Biology 5158 2015 Paper 2 Answer Scheme Qn Answers Remarks 1a A: Starch B: Amylase C: Maltose Common mistake: Did not state precise names of the substances A, B and C. Bi Temperature Ii pH c A blockage in bile duct will prevent delivery of bile to duodenum. Emulsification of fats cannot occur. Surface area for lipase to act on fats decrease. Hence, blockage in bile duct will result in decrease in fats digestion. Common mistakes: Candidates did not state the application of consequence of a bile duct. Candidates need to state clearly the understanding of differences between physical and chemical digestion. Important for candidate to state that fat digestion is slowed down as compared to completely stopped. 2a Sexual reproduction involves the fusion of male and female gamete to produce a zygote. Gametes are products of the process of meiosis. During fertilisation, fusion of haploid gametes are at random and zygote formed is diploid. Offspring from sexual reproduction are genetically dissimilar to parents. Good responses includes production of genetically dissimilar offspring and references to meiosis were made.

2b The pollen grain is spherical in shape and has a rough surface with spikes evenly distributed that enable the pollen grain to cling on the body of animals when they brush pass the flowers. These pollen grains can then be transferred from the anther of a flower to a stigma of another flower when the animals brush past another flower. 2ci Pollen tube 2cii After pollination, pollen grain germinates in response to sugary fluid secreted by mature stigma. A pollen tube grows out from the pollen grain. Growth of pollen tube is controlled by the pollen tube nucleus. The cytoplasm and the two nuclei pass into the pollen tube. The pollen tube secrets enzymes to digest the surrounding tissue of stigma and style. Pollen tube enters the ovule through the micropyle. The generative nucleus divides into two male gametes, while the pollen tube nucleus disintegrates. When the pollen tube reaches the ovule, its tip absorbs sap and bursts, releasing the two male gametes. One male gamete fuses with the ovum to form the zygote (fertilisation). The other male gamete fuses with the definitive nucleus to form the endosperm nucleus. Zygote divides and develops into the embryo, and the endosperm nucleus will give rise to an endosperm (food storage tissue) Need to give a detailed description of how the pollen tube reach the female nucleus 3a 40-16 = 24oC

B 1. There was a rise in body temperature of the insect when the air temperature increases. 2. The insect was not able to maintain a constant body temperature. Common mistake Was not able to give a second conclusion 3c Constant body temperature at 37oC Common mistake Not able to show the body temperature at 37oC in the graph 3d When body temperature increases, the hypothalamus detects the change. Sweat glands become more active to increase production of sweat. Latent heat of vapourisation is lost when sweat evaporates to reduce body temperature and bring the body temperature back to normal. When body temperature decreases, the hypothalamus detects the change and sweat glands becomes less active to decrease production of sweat. Candidates need to understand how sweating cools the body. 4a A: Aorta B: Pulmonary vein 4b The semi lunar valve in the aorta prevents the backflow of blood from the aorta to the left ventricle, when the ventricle relax to ensure that blood flows in one direction from the ventricle to the aorta to the rest of the body. Common mistake Lack of precision in exact location of the valve 4c Deoxygenated blood is brought back to the heart via the superior and inferior vena cava. Contraction of the right atrium forces the blood to the right ventricle. The right atrium relax and the right ventricle then contract to bring the blood to the lungs via the pulmonary artery. Tricuspid valve closes to prevent the backflow of blood back to the right atrium from the right ventricle. When the right ventricle relax, the semilunar valve in the pulmonary artery closes to prevent the Candidates need to do both description and explanation to gain the full marks. Candidates should show understanding of the processes involved.

backflow of blood from the artery to the right ventricles. 5a Change in concentration of insulin decrease by 90 arbitrary units. Common mistake Lacking precision in response to the question 5b During fasting, there is no intake of carbohydrates, causing the blood glucose concentration to decrease below normal. Islet of Langerhans is stimulated to increase production of glucagon which stimulates the liver and muscle cells to convert glycogen to glucose. This will increase blood glucose concentration. Concentration of blood glucose concentration increases and blood glucose level returns back to normal. Feedback is sent to the islets of Langerhans to reduce the production of glucagon. Blood glucose concentration is maintained at normal concentrations by negative feedback. The initial increase in insulin after a meal to decrease blood glucose level causes the concentration of blood glucose level to decrease, resulting in negative feedback, and hence, there is a reduction in level of insulin when the person start fasting to prevent further decrease in blood glucose level. Good level of details is needed. Correct descriptions also made references to negative feedback Common mistake Candidates need not include unnecessary detail that did not answer to the question at the start of the answers Precise answers with references to the blood rather than the body in general 5c Adrenaline helps to convert stored glycogen to glucose. Glucose is needed for respiration during exercise to release more energy when oxidized. Adrenaline also increases heart rate and blood flow to ensure that oxygen and glucose are transported to the respiring muscles faster. Common mistake Production of energy instead of release of energy 6ai IAIo 6aii IBIo

6aiii Child 2: Blood group AB Child 4: Blood group O Common mistake in stating the blood group of child 4 6b Alleles IA and IB are co-dominant. Common error Unclear if candidates were quoting genotype IAIB or identifying alleles separately. Blood group phenotype A and B stated were stated instead. 7ai An organism that obtains its energy by feeding on other organisms. Common mistake Repeating of term in definition without showing understanding of meaning of the term 7aii Level of organism in a food chain Common mistake Unable to define trophic level 7bi Plankton  small fish  large fish  fishermen Candidates should give the relevant names in their chains. 7bii Bioaccumulation is the transfer and accumulation of certain chemicals that are toxic that cannot be broken down and are not excreted out of the bodies of organisms. The toxins are stored in the fatty tissues and accumulate in their bodies. The toxins are then passed along the food chain and become concentrated in the bodies of the final consumers. Mercury is non-biodegradable and not excreted. Plankton takes in the mercury compounds, hence, the storing the mercury in its cells. The small fish feeds on plankton and accumulates the mercury that cannot be excreted, causing the flesh of the small fish to have 100 times more mercury than the seawater. Good responses shows understanding of impact on small fish. Common mistake Not reading question properly and commenting on the larger fish instead of showing understanding of the impact on the small fish

8a Graph to include an anomaly, ensure that the label of axis follow strictly the heading of table provided Common mistake Time of hour instead of time of day 8b 0.04-0.014=0.026 8c The carbon d