2024 MFSS 4Exp 5088 Sci Bio Prelim P4 MS

2024 4E SC-Bio 5088 P4 Prelim Exam Marking Scheme Section A Qn Expected Ans mark s Remarks 1a) % increase in 0.8%: Working : (8.2-7.5)/7.5 Answer: 0.09333 0.0933 % (3 sign fig) 1 1 (b)(i) rbc in 1.8%: reduced in diameter from 7.5 to 6.0µm 1.8% salt solution has lower water pot than rbc = so water moved out of rbc by osmosis and thus the cell shrunk 1 1 Poorly done. Data not cited (ii) No change in size in 0.9%: water potential of rbc sap is the same as the water potential of 0.9% salt solution. 1 Also accept same salt concentration Water concentration rejected 5m 2a Scale for many students penalised; should not include pH 1-2. b Test for starch : add a few drops of iodine solution to starch Result: if starch present, solution turns blue-black. If starch is absent, solution remains yellow/brown. 1 1 c Opt pH = read from graph 6.4 (betw pH 6 & 7) 1 Many students did not read from the graph. Cited pH from the table directly not accepted. d Starch is digested in the mouth by amylase into maltose. Maltose is digested in small intestine by maltase into glucose 1 1 mention place, enzyme & product 8m 3a i) Heart rate = at rest was 65-66 beats per min but after exercise went up to 110 beats but slowly went back to 68 after few min. 1 Data cited with no units not given credit. Coord=1m Accurate pts = 1m Best fit curve =1m

No. of beats went up bec heart beats faster to send oxygen and glucose quickly to the muscles / muscles need oxygen and glucose for respiration /to provide energy to muscles 1 Common mistake: blood provides energy to the body; blood circulated to the rest of the body (with no mention of the muscles receiving more blood for muscular contractions) ii) Percentage of oxygen: slight decrease from 98-99% at rest to about 96% Muscles require oxygen for respiration but lungs not able to get enough oxygen into the bloodstream. 1 1 Almost no student was able to cite the limited capacity of the lungs to obtain sufficient energy to support aerobic respiration. Many students mistakenly wrote that anaerobic respiration kicks in instead of aerobic respiration. iii) Faster breathing (increase in breathing rate) OR deeper breathing (depth of breathing) 1 Many cited breathing through nose or mouth (not accepted) without considering how the measure must increase the amount of oxygen supplied. b Any 2 of the following: Emphysema – alveolar wall breaks down = so surface area for gaseous exchange is less. 1. Pulse rate is usu higher in smokers. They need to pump blood harder to get blood to all parts of body. 2. % oxygen in blood – usu lower than non-smoker. As they are not able to take in maximum oxygen at each breath, oxygen saturation is usu lower. 1 1 1 7m 4a i) 1 1 Many labelled X/Y without the name of the structure or vice versa. T