CCHY 2012 Bio Yearly TYS ANS

6093 Biology Yearly TYS 2012 No Paper 1 Marks Remarks 1 B 1 2 C 1 3 D 1 4 D 1 5 A 1 6 A 1 7 C 1 8 B 1 9 C 1 10 D 1 11 C 1 12 C 1 13 B 1 14 C 1 15 D 1 16 B 1 17 C 1 18 D 1 19 D 1 20 C 1 21 C 1 22 B 1 23 A 1 24 A 1 25 D 1 26 C 1 27 C 1 28 A 1 29 B 1 30 C 1 31 A 1 32 D 1 33 A 1 34 B 1 35 A 1 36 C 1 37 C 1 38 B 1 39 D 1 40 B 1 Total 40

Paper 2 Section A 1a Gene is a unit of inheritance, born on a particular locus of a chromosome; gene is a small segment of DNA in a chromosome, made up of a sequence of nucleotides that codes for the production of polypeptides; 1 1 1bi Both parents are Aa. 1 1bii 3:1 1 1biii AA, Aa 1 Total 5 2a Larger sample size to increase accuracy of results + offset any anomaly in readings 1 2b amount of urea increased almost 4 times when amount of protein increases from low protein level at 4.75g of urea per day to normal protein level at 19.2g of urea per day; amount of urea increased almost 6 times when amount of protein increases from low protein level at 4.75g of urea per day to high protein level at 31.5g of urea per day; 1 1 Compare low and normal Compare low and high 2ci Protein At glomerulus, proteins are retained in the glomerular capillaries; they are too large to pass through the walls of the glomerular capillaries and the partially permeable basement membrane; Glucose High hydrostatic blood pressure in glomerulus forces glucose out of glomerulus into Bowman’s capsule by ultrafiltration; At PCT, most glucose are selectively reabsorbed through the walls of the tubule into the surrounding blood capillaries by diffusion and active transport + glucose are required by the body + reabsorbed readily; 1 1 1 1 2cii 0.015 ÷ 0.01 = x1.5 1 Total 8

3ai A: hair B: blood capillary D: adipose tissue 1 1 1 3aii body temperature is higher than normal level detected by the thermoreceptors, stimulates hypothalamus which in turn stimulates sweat glands to become more active; Increased production of sweat + more water in sweat evaporates into water vapour from skin surface; More latent heat of vaporisation is lost from body + lose heat + temperature is restored to normal level; 1 1 1 Stimulus + gland + effect 3bi 37.1 – 36.72 = 0.38 1 3bii Decreased metabolic rate; reduce the amount of heat released; / Sweat glands are more active; results in more sweat produced, more water in sweat evaporates into water vapour, more latent heat of vaporisation lost; / Dilation of arterioles; allow more blood flow + more heat loss by radiation, convection, conduction; 1 1 Total 9 4ai Carbon dioxide + water glucose + oxygen 1 R: no conditions, sunlight 4aii chloroplasts 1 4aiii Palisade mesophyll cell 1 R: layer 4bi stomata 1 R stoma 4bii Open in presence of light to allow gaseous exchange where carbon dioxide diffuses in and excess oxygen to diffuse out when rate of p/s exceeds rate of r/p + water vapour to diffuse out of leaf to increase rate of transpiration; Close to reduce water loss + prevent wilting; 1 1 4c C 1 Total 7 chlorophyll light

5ai A: red blood cell B: tissue fluid 1 1 5aii Arrow must be drawn from RBC through the walls of capillary, through tissue fluid, through the cell surface membrane into the cells 1 R: multiple arrows 5aiii Phagocytes can destroy foreign particles that enter the blood by engulfing and ingesting + ingested foreign particle will be digested; Lymphocytes produce antibodies + - antibodies destroy bacteria by attaching to them and causing the surface membrane to rupture/ - causing bacteria to clump together/agglutinate so that they can be easily ingested by phagocytes/ - neutralising the harmful toxins produced by bacteria; 1 1 Phagocytosis Production of antibodies + 1 function of antibodies 5b Group A Group AB 2 1 Total 8 6ai Amount of catalase present in the increasing number of discs of potato tissue 1 6aii Volume of hydrogen peroxide used for each test tube; Temperature of mixture in each test tube; 1 1 6aiii A test tube with only hydrogen peroxide without any potato 1 6b The higher the amount of discs of potato tissue, the higher the amount of catalase, the higher the rate of breakdown of hydrogen peroxide into water and hydrogen, the more froth produced 1 Total 5

7a A: nucleus B: mitochondrion C: Golgi apparatus 1 1 1 7bi For each pair of homologous chromosome, only one member enters a single gamete. Pg 311, 307 2 A: any other possibilities 7bii Ovary/ Testis 1 Total 6

Section B 8a correct orientation; All points plotted correctly; Best fit line; Graph occupies at least 2/3 of grid; 4 8b 65 – 20 = 45 cm3 per litre 1 8c 194 – 40 =154 cm3 per litre 1 8d level of exercise increases, muscles contract more vigorously + increase amount of oxygen used up; increase demand for oxygen due to increase rate of aerobic respiration; breathing rate increases to inhale more air at a faster rate; heart beats faster so that more oxygen can be transported by blood to muscles at a faster rate; 1 1 1 1 Relationship Explain Effect Effect Total 10 0 20 40 60 80 100 120 140 160 180 0 20 40 60 80 100 120 140 oxygen content of blood (cm3 per litre) level of exercise (a.u.) Graph of Oxygen Content of Blood against Level of Exercise

9a Water continuously moves out of the mesophyll cells to form a thin film of moisture over the surfaces of spongy mesophyll cells by osmosis; Water potential of cell sap in mesophyll cells decreases + mesophyll cells absorbs water by osmosis from the cells deeper in the leaf; Water evaporates from the thin film of moisture and moves into the intercellular air spaces in the spongy mesophyll layer; water vapour accumulates in the large air spaces near the stomata creating a higher concentration of water vapour in the leaf than outside the leaf; water vapour diffuses out of leaf through the stomata; 1 1 1 1 1 Thin film of moisture Compare WP intercellular air spaces compare conc. of water vapour Diffusion 9b Moving air blows away water vapour that accumulates outside the stomata + creating a lower humidity/ lower conc. of water vapour; Maintains steep water vapour concentration gradient between the leaf and the atmosphere continuous diffusion of water vapour out of leaf + higher rate of transpiration than that of still air; still air makes water vapour accumulates/ higher humidity/ high concentration of water vapour outside leaf + lower rate of transpiration than that of moving air; 1 1 1 1 9c Aerobic respiration 1 Total 10

E10a Similarities 1. Both require receptor to detect a stimulus 2. Both involved the transmission of nerve impulses along the sensory neuron and motor neuron 3. Both involves an action carried out by effectors Differences 1. VA is a deliberate action with conscious control but RA is an immediate response to a specific stimulus without conscious control. 2. In VA, nerve impulses are transmitted to the relay neurons in the brain for processing and decision-making but in RA, nerve impulses are not transmitted to the brain for processing and decision-making until after the RA has been carried out by the effector. 3. In VA, the pathway travelled by the nerve impulse from receptor to effector is longer than that in RA. 4 E10b Knee-jerk reflex + Sudden tapping below the kneecap; Stretch receptor receives stimulus + produces nerve impulses; Nerve impulses transmitted along the sensory neurone to relay ne