2022 SASS Bio 4E MYE Ans

Mid-Year Examination 2022/4Exp/Biology/Ans Paper 1 – MCQ 1 A 11 D 21 A 31 C 2 B 12 D 22 A 32 B 3 A 13 C 23 A 33 B 4 C 14 D 24 B 34 C 5 A 15 A 25 C 35 C 6 C 16 D 26 C 36 D 7 B 17 C 27 B 37 C 8 C 18 A 28 D 38 D 9 B 19 D 29 D 39 C 10 D 20 C 30 C 40 D Paper 2 – Section A (50 marks) Answer Marks Marker’s Report 1a A - digestion B - absorption C - deamination D - excretion Any 2 correct for 1 mark 2 1b Trypsin Peptidase 1 1 R: pepsin (Qn states small intestine) 1c - Amino acids are absorbed from the lumen of the small intestine into the blood capillaries of the villi - Through diffusion and/or active transport depending on difference in concentration gradient between small intestine and blood capillaries 1 1 Some did not specify villi / missed out on active transport. 1di 1 R: respiration (too vague) 1dii glucose + oxygen  carbon dioxide + water + energy 1 R: carbohydrate Some left out energy. aerobic respiration 1

Mid-Year Examination 2022/4Exp/Biology/Ans 1e - water potential of blood plasma increases / water potential of blood plasma is higher than blood cells - causing water molecules to move from blood plasma into blood cells - by osmosis - blood cells will swell / burst Any 2 for 1 mark 2 R: water Some left out name of process. 2a 5000 – 1500 = 3500 cm3 1 R: no units 2b - diaphragm relaxes and arches upwards - external intercostal muscles relax, - internal intercostal muscles contract - ribs move downwards and inwards - thoracic volume decreases - atmospheric pressure now lower than pressure in lungs - air is forced out of lungs Any 2 for 1 mark 3 R: pressure decreases (must show comparison) 2c Both increase in frequency + increase in volume must be observed 1 Drawings between V and W would not be marked. Poorly done. Most students indicated an increase in volume but not frequency. 2d Spirogram of person suffering from chronic bronchitis would indicate a increase in speed / decrease in volume of air inspired and expired by the lungs. 1 A: smaller wavelength / amplitude 3a - Down’s syndrome - It is a disease caused by an extra copy of chromosome 21 present. 1 1 Accept any other valid ans 3bi From prophase I to anaphase I 1 R: prophase to anaphase 3bii - During prophase I, the newly replicated chromatin threads condense to form chromosomes - During anaphase I, homologous chromosomes are separated to opposite poles of the cell 1 1 Some simply repeated information in the question 2

Mid-Year Examination 2022/4Exp/Biology/Ans text rather than substantiating with the processes that specifically happens in those stages. 4ai - Suggest: Increase in adrenaline - Explain: Stimulate conversion of glycogen to glucose OR - Suggest: After a meal high in sugar / starch / carbohydrates / glucose - Explain: Glucose is absorbed / diffused into the bloodstream by the small intestine 2 Some students showed no / weak understanding of the concept of homeostasis. 4aii - Suggest: blood glucose concentration falls below norm - Explain: Islet of Langerhans secrete glucagon / hormone Q into the bloodstream to convert glycogen back to glucose 1 1 Many left out “before norm” 4bii P – adrenaline Q – glucagon 1 1 Poorly done. P is not insulin, increase in P occurred before increase in blood glucose level. 4bii i - (Adrenal) gland stop producing the hormone - Hormone broken down by liver 1 1 ECF if P was wrongly identified as another hormone. 1m - feedback sent to receptor / islet of Langerhans stop producing hormone 1m- hormone broken down by liver 5a - Gene/ genetic mutation 1 Well done 5b - Discontinuous variation - Phenotypes are clear-cut/distinct/no intermediate between resistance or susceptibility to warfarin 1 1 A: controlled by 1 gene Some students are not clear on the difference between continuous and discontinuous variation. 5c Parent 1 Parent 2 phenotype of parents Resistant Susceptible genotype of parents Rr rr gametes R r r r genotype of offspring Rr rr Rr rr phenotype of offspring Resistant Susceptible Resistant Susceptible 1 1 1 1 Well done. 3

Mid-Year Examination 2022/4Exp/Biology/Ans Paper 2 – Section B (30 marks) 5d - mutation in VKORC1 gene has resulted in some rats becoming resistant to warfarin, while some remain succeptible / variations in population - during incidents of rat extermination, competition between the variants occur - rats that are resistant to warfarin survive, reproduce and pass on favourable genes to their offspring - rats that are succeptible to warfarin die off over time and decrease in numbers in the population - rats that are resistant to warfarin become the predominant species in the environment - rats are said to have evolved Any 2 for 1 mark 3 Many students only got partial credits by mentioning mark points 3 and 4. Some used extremities like “all rats susceptible will die off”. Some fail to associate the question to natural selection and evolution. 6a - circled a single nucleotide - labelled sugar/deoxyribose, nitrogenous base and phosphate group accurately (3 correct labels for 2m, 2 correct labels for 1m) 1 2 Generally well done, a few mixed up phosphate and sugar. 6b - hydrogen bonds - formed between bases according to rules of complementary base pairing - holding the two polynucleotide strands together / forms a double helix 1 1 1 Many fail to establish that the bonds hold the 2 polynucleotide strands together. 6c (100% - 38% - 38%) / 2 = 12% 1m for correct working, 1m for correct ans with units 2 Well done. 6di - UUA GAU AGU AGU CGU AAG 1 Well done. 6dii - Order of bases in a DNA determines the order of bases in the mRNA formed during transcription - Order of bases in the mRNA then determines the o rder of amino acids on the polypeptide formed during translation 1 1 Poorly done. Most simply stated that order of bases affected polypeptide sequence. 4

Mid-Year Examination 2022/4Exp/Biology/Ans 7ai 1– Scale 1– line 1– Axis 1– Plot points Scale – graph has to fill at least ½ of the grid provided line – both curve and line accepted Axis – appropriate labels with units for blood pressure indicated Plot points – accurate to data provided Generally okav, however some students went to find average blood pressure despite question clearly asking for range. 7aii - Blood pressure is highest in the arteries, 115-120mmHg and lowest in the veins, 10-15mmHg - Blood pressure decreases from 120 to 10 mmHg as blood moves from arteries to arterioles to capillaries and finally to veins / away from the heart - Blood pressure differs in each type of blood vessels - Greatest fall in blood pressure occurs in the arterioles from 115 to 40 mmHg - Greatest range of blood pressure occurs in the arterioles from 40 to 115mmHg Any 2 2 Many did not quote values. If 2 points were given but no data quoted at all, max 1m. If 1 point given without data, 0m. 7aii i - Blood pressure in the arteries is higher than the blood pressure in the veins - Hence arteries require thicker walls than veins to withstand the higher blood pressure / to prevent rupture of vessel 1 1 R: thickness of wall is dependent on blood pressure in vessel (must specify which has the thicker wall and higher pressure) 7bi Prevents the mixing of deoxygenated blood in the right side with the oxygenated blood in the left side of the heart 1 R: mixing of blood in the left and right side of the heart (vague) 7bii Pulmonary artery 1 R: pulmonary arch 7bii i - Blood is being pumped through the lungs at a higher pressure and as such is flowing quicker through the lungs - Insufficient time for blood to be well oxygenated 1 1 A: blood flows from LV to RV, less oxygenated blood flows to all parts of body R: blood absorb oxygen 8a - Placenta / embryonic villi 1 Many students only cited diffusion of nutrients from mother’s blood into 5

Mid-Year Examination 2022/4Exp/Biology/Ans - nutrents and oxygen may not reach foetus