CCHY 2021 Bio Yearly TYS ANS

6093 Biology Yearly TYS 2021 No Paper 1 Marks Remarks 1 C 1 2 B 1 3 D 1 4 D 1 5 A 1 6 D 1 7 C 1 8 C 1 9 B 1 10 A 1 11 B 1 12 A 1 13 B 1 14 B 1 15 A 1 16 D 1 17 C 1 18 A 1 19 C 1 20 D 1 21 A 1 22 A 1 23 D 1 24 D 1 25 D 1 26 C 1 27 B 1 28 C 1 29 C 1 30 C 1 31 B 1 32 C 1 33 C 1 34 B 1 35 A 1 36 C 1 37 D 1 38 B 1 39 A 1 40 D 1 Total 40

Paper 2 Section A No Answers Marks Remarks 1a P: vena cava Q: right atrium 1 1 1b contains oxygenated blood from the aorta; transporting oxygen and digested food/nutrients to heart muscles; 1 1 type content 1c oxygen dissolves in the thin layer of moisture lining the alveolar walls; oxygen diffuses from the thin layer of moisture through the alveolar walls and the capillary walls into the bloodstream; oxygen diffuses into the red blood cells and combines with haemoglobin to form oxyhaemoglobin; red blood cells carry oxygen from the capillaries to the pulmonary veins to the left atrium, followed by left ventricle, out of the heart through the aorta to the renal artery to the kidneys; 1 1 1 1 dissolves in TLM diffuse out of alveoli diffuse into RBC pathway to kidney 1d When blood vessels are damaged, damaged tissues and platelets releases thrombokinase, wh ich catalysed the conversion of prothrombin into thrombin in the presence of calcium ions; thrombin catalyses the conversion of soluble fibrinogen into insoluble fibrin threads that entangle blood cells forming a clot; 1 1 action of thrombo- kinase action of thrombin Total 10

No Answers (CLT) Marks Remarks 2ai 1 division  90 au ÷ 36 divisions = 2.5 au 6 divisions  2.5 au × 6 divisions = 15 au energy used for growth = 15 au/year 1 2aii heat/ thermal energy 1 2aiii 90 – 15 – 25 = 50 au/year 1 2b 15 90 × 100% = 16.7% 1 1 2c when rate of respiration in animals increases due to increase movement/ increase muscular contraction , animal body temperature increases, resulting in an increase in the release of heat from the body by radiation, conduction and convection; restricting movement of animals will reduce energy lost to the environment in the form of heat and increase energy available for growth; chemical potential energy in food consumed by animals will be stored and used for growth of muscle cells resulting in bigger size animals that will produce more meat when slaughtered; 1 1 1 increase heat released reduce energy lost energy for growth Total 8

No Answers Marks Remarks 3a B – salivary amylase; C – pancreatic amylase/ trypsin/ maltase/ lipase; A – pepsin; 2 2 2 3b digestive enzymes are specific in action whereby each chemical digestion is catalysed by a unique enzyme due to its three- dimensional shape; only a specific substrate can bind to the active site of enzyme to form an enzyme-substrate complex i.e. amylase can only bind to starch and maltase can only bind to maltose; digestive enzymes works best at an optimum temperature of about 37°C (body temperature) and at different optimum pH depending on location + denature at extreme pH values; 1 1 1 specificity e-s complex effect of pH & temp Total 9

No Answers Marks Remarks 4a 1 1 1 1 4b 0.25 or 25% or ¼ 1 4c mother can produce the enzyme needed to break down phenylalanine; enzymes diffuses from the maternal blood system into the fetal blood system in the placenta resulting in no build-up of amino acids in the fetal blood; 1 1 presence of enzyme diffusion 4d Down’s syndrome 1 Total 8 Affected Carrier, unaffected Carrier, unaffected Nn Nn father mother Genotype of parents Gametes Genotype of offspring Phenotype of offspring N n N n NN Nn nn Nn Non-carrier, unaffected

No Answers Marks Remarks 5a Process by which metabolic waste products and toxic substances are removed from the body of an organism; Metabolism produces waste products which can be toxic when accumulated in the body and cause harm to the organism so must be removed immediately; 1 1 definition effect/ importance 5bi one arrow labelled T to show direction from glomerulus to Bowman’s capsule 1 5bii one arrow labelled U to show direction from PCT to blood capillaries 1 5c low concentration of ADH in the bloodstream stimulates cells in the walls of the V to become less permeable to water resulting in decrease water reabsorption from the V into the blood capillaries; high concentration of ADH in the bloodstream stimulates cells in the walls of the V to become more permeable to water resulting in increase water reabsorption from the V into the blood capillaries; 1 1 low ADH high ADH 5di both dialysis fluid and blood plasma contains essential substances such as glucose, amino acids and mineral salts dissolved in water; dialysis fluid does not contain metabolic waste products but blood plasma contains metabolic waste products such as urea, uric acid, creatinine, excess water and excess mineral salts; dialysis fluid does not contain protein molecules but blood plasma contains protein molecules such as hormones; 1 1 1 similarity difference difference 5dii maintains a steep concentration gradient for the removal of metabolic waste products from the blood; maintains a correct solute composition and water potenti al in the blood by allowing essential substances to diffuse from the dialysis fluid into the blood; 1 1 Total 11

No Answers Marks Remarks 6 a fragment of DNA in huma n chromosome that contains the insulin gene is obtainedby by using restriction e nzymes to cut restriction site of insulin gene at the two ends of the gene to produce sticky ends; a plasmid from a bacterium is obtained by cutting plasmid with the same restriction enzymes producing complementary sticky ends to the ends of the insulin gene; mix the plasmid with the DNA fragment containing the insulin gene to allow the DNA to bind to plasmid by the complementary base pairing between their sticky ends + DNA ligase is used to seal the bonds, forming a recombinant plasmid; mix recombinant plasmid with E.coli bacterium and apply temporary heat or electric shock to open up pores in the cell surface membrane of the bacterium for the plasmid to enter , forming a transgenic bacterium; 1 1 1 1 cutting of insulin gene cutting of plasmid formation of recombinant plasmid formation of transgenic bacterium Total 8

Section B No Answers Marks Remarks 7ai 4 Axes labelled + all ticks labelled at equal intervals; Best fit line + no shading + smooth curve; All points plotted accurately; Maximise the size of grid provided; 7aii 0.33 mol dm-3 1 ±0.1 7aiii 0.50 % 1 ±0.1 7b when water potential in the potato cells is lower than water potential in the sucrose solution, water molecules enter the potato cells down water potential gradient by osmosis; causing potato cells to increase in length resulting in the positive percentage change in length of potato strip; when water potential in the potato cells is higher than water potential in the sucrose solution, water molecules leave the potato cells down water potential gradient by osmosis; causing potato cells to decrease in length resulting in the negative percentage change in length of potato strip; 1 1 1 cause of increase length cause of decrease length both effects 7c vacuole shrinks/ cell membrane shrinks away from cell wall 1 Total 10 -6.0 -4.0 -2.0 0.0 2.0 4.0 6.0 8.0 0 0.2 0.4 0.6 0.8 1 percentage change in length/ % concentration of sucrose solution/ moldm-3 Grap