2023 Pure Biology Practical Answers

Exhaled air contains carbon dioxide gas;  carbon dioxide gas dissolved in water to form carbonic acid / is an acidic gas, changes the colour of pH indicator from green to yellow

35.0 2 min 15 s 2 min 32 s 17 2 min 40 s 2 min 55 s 15 3 min 30 s 3 min 43 s 13 3 min 57 s 4 min 10 s 13 4 min 35 s 4 min 48 s 13 15 + 13 + 13 + 3 4 = 14 11 min 55 s 12 min 48 s 53 13 min 2 s 13 min 54 s 52 14 min 10 s 14 min 50 s 48 15 min 30 s 16 min 3 s 33 16 min 18 s 16 min 35 s 15 35.0 53 + 52 + 48 3 = 51

Time for all test-tubes not consistent / similar / varies; OR first test tube for each yeast suspension takes a longer time compared to the rest of the test tubes; OR some results are anomalous / outliers; relevant data, i.e timing quoted from table 15 71.4 10 18.6 Mean rate of respiration for 15% glucose = 1000 / 14 = 71.4 Mean rate of respiration for 10 % glucose = 1000 / 51 = 19.6

Respiration is an enzyme-controlled reaction + temperature affects enzyme activity. Hence, temperature affects rate of respiration The exact timing / moment when solution turns yellow is subjective or difficult to be consistent in deciding/ determining the timing the solution turns yellow; Hence recorded time / results are inconsistent or longer or shorter than the actual end-point

15% glucose has a higher substrate concentration + higher frequency of collisions between glucose and enzyme + higher rate of enzyme-substrate formation. Use a gas syringe to measure volume of gas produced in a fixed duration of time Use boiled and cooled mitochondria suspension / water instead of mitochondria suspension; In the control set up, carbon dioxide is not produced and the indicator should not change in colour. This shows that mitochondria is the only source carbon dioxide. Volume of mitochondria suspension / glucose Concentration / mass of glucose used to prepare mitochondria suspension; Concentration of mitochondria suspension ; pH of mitochondria suspension ; Length of time taken before the results is taken;

Accuracy: number of grooves + shape; Proportion: middle villi x2 longer Left villi is slightly longer than right villi Line