CCHY 2019 Bio Yearly TYS ANS

6093 Biology Yearly TYS 2019 No Paper 1 Marks Remarks 1 B 1 2 D 1 3 C 1 4 B 1 5 D 1 6 D 1 7 B 1 8 C 1 9 B 1 10 A 1 11 D 1 12 B 1 13 B 1 14 C 1 15 D 1 16 A 1 17 C 1 18 C 1 19 C 1 20 D 1 21 C 1 22 D 1 23 B 1 24 D 1 25 C 1 26 A 1 27 D 1 28 D 1 29 A 1 30 A 1 31 C 1 32 C 1 33 A 1 34 D 1 35 D 1 36 D 1 37 D 1 38 A 1 39 B 1 40 C 1 Total 40

Paper 2 Section A 1ai Cell surface membrane/ cell membrane; Partially permeable + controls substances entering or leaving the cell by allowing only some substances to pass through; 1 1 1aii Ribosome; Attached to the ER + synthesise proteins that are usually transported out of the cell; 1 1 1b Large number of mitochondria releases large amount of energy by aerobic respiration + many functions carried out by liver; Many vital functions e.g. regulation of BGC/ production of bile to emulsify fats into smaller fat droplets in small intestines/ breakdown of haemoglobin and storage of iron/ synthesis of proteins such as prothrombin and fibrinogen/ deamination of amino acids into ammonia and then urea/ detoxification of alcohol into acetyledehyde by alcohol dehydrogenase 1 1 1c Cellulose cell wall Chloroplast Large central vacuole 2 1d Increase surface area to volume ratio + increasing the rate of absorption of digested food substances through the epithelium of villi; epithelium is made up of epithelial cells with microvilli + epithelium is one-cell thick to shorten diffusion distance for faster absorption of digested food; 1 1 Total 10

2a A: right atrium + B: left atrium + C: right ventricle + D: left ventricle; A and B have the same lowest thickness of 3mm + thinner muscular walls compared to the C and D + they only force blood into the ventricles + does not need to withstand high pressure; D has a thicker muscular wall of 12 mm compared to C (5 mm) + to withstand higher pressure than that in C + to pump blood round the whole body; C has a thinner muscular wall of 5mm compared to D (12 mm) + need to withstand lower pressure than that in D + to pump blood to lungs located close to the heart; 1 1 1 1 R: no quotation of data 2b Oxygenated blood in the left atrium will mix with the deoxygenated blood in the right atrium + amount of oxygenated blood flowing into left ventricle , aorta and the rest of the body is reduced/ lowered; Blood transports less oxygen (hypoxemia) + insufficient oxygen supply for aerobic respiration in cells (hypoxia) + body cannot function as per normal/ feels tired easily/ lacks energy to function; 1 1 2c Atherosclerosis 1 Total 7

3a Water molecules move from 1 (xylem) to 2 ( mesophyll cell) by osmosis down water potential gradient; Water molecules moves out of the mesophyll cells by osmosis to form a thin film of moisture over surfaces of the mesophyll cells; Water evaporates from the thin film of moisture into water vapour + moves in to 3 ( intercellular air spaces ) + w ater vapour accumulates in the large air spaces near the stomata; creating a higher concentration of water vapour in the leaf than the air outside the leaf + wa ter vapour diffuses out of leaf through 4 (stoma) into 5 (surrounding air); Water potential of cell sap in mesophyll cells decreases + mesophyll cells continuously absorbs water by osmosis from 1 + r esults in a suction force that pulls water up the xylem vessel (transpiration pull); 1 1 1 1 1 3b J: Upper epidermal cell Adaptation: no chloroplasts + allowing maximum light to pass through and reach mesophyll layer; K: palisade mesophyll cell Adaptation: numerous chloroplasts + absorb light for photosynthesis; 1 1 1 1 3c In daylight, p/s occurs, rate of p/s is higher than rate of r/p + carbon dioxide is rapidly used up in the leaf; Concentration of carbon dioxide in the leaf becomes lower than that in atmospheric air creating a diffusion gradient + carbon dioxide diffuses into the air spaces of the leaf through opened stomata; Oxygen production increases due to increase rate of p/s + excess oxygen diffuses out of the leaf through opened stomata; Water vapour accumulated diffuses out of the leaf through the opened stomata + increasing rate of t/p + increasing transpiration pull + plant cells continuously absorbs water + maintains turgidity of cells; 1 1 1 1 Total 13

4a 1 1 1 1 4b d d D Dd Dd d dd dd Using Punnet squares to determine the probability, chance of every child not having cystic fibrosis but are carriers is 50% + ratio applies to every child independent of number of offspring/ actual ratio is far from expected ratio because smaller sample size is used to obtain the expected ratio 1 4c Mutation is a sudden random change in the structure or in the chromosome number of a gene; Error may occur during replication of gene or chromosome + error is not repaired + gene is modified/ chromosome is altered + inherited by offspring through fertilisation; 1 1 4d Exposure to UV light/ X-rays/ carcinogens/ mutagens/ alpha, beta and gamma radiation/ chemicals like tar and formaldehyde in cigarette smoke/ lysergic acid diethylamide (LSD) drug; 1 Total 12 Affected Carrier, unaffected Carrier, unaffected Dd Dd father mother Genotype of parents Gametes Genotype of offspring Phenotype of offspring D d D d DD Dd dd Dd Non-carrier, unaffected

5ai C C G A T A 1 5aii nucleotide 1 5ab Social implications: May cause allergies in humans/ Easier and cheaper to produce medicine + more affordable + more patients can get access to them and be treated/ Higher risk of contamination by disease -causing microorganism present in chickens/ Loss of biodiversity due to drop in population of chickens/ May be toxic or cancer -causing + modifying a single gene could result in alteration of metabolic processes producing unwanted toxins/ Ethical implications: Vegetarians or religious groups will object the use of medicine obtained from animals/ Morally wrong to exploit animals for medical research/ Deliberate creation of new combinations of genes that may be used in chemical or biological warfare/ Any 2 Any 2 Total 6 6a Energy is lost through metabolic processes e.g. aerobic respiration in the form of heat/ thermal energy; Energy is lost through the excretion of undigested matter/ leftover of the parts of animals that are inedible or unconsumed in the form of chemical energy; 1 1 6b 1600 − 90 1600 × 100% = 94.375% = 94% 1 1 6c About 90% of energy lost at every trophic level/ only about 10% of energy transferred to the next trophic level; small amount of energy available at the highest trophic level; 1 1 Total 6

Section B 7ai 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; 4 7aii 10.2% ± 0.5 1 7bi % of fish caught is slight increase for the first 10 years from 1993 to 2003 with percentage ranges from 5.0 % to 5.6 %; % of fish caught increases rapidly after 2003 to 2008 from 5.6 % to 7.2 % + increases rapidly after 2008 to 16.3 %; 1 1 R: no quotation of data 7bii Large % of big fishes indicates that there are higher number of predators/ secondary and tertiary consumers; Implying that there is a larger population of primary consumers to support the large population of secondary and tertiary consumers + sufficient amount of producers for the primary consumers to thrive/grow and reproduce; Indicating that the populations are healthy + growth and reproduction are not