AHS_2021_S4_6093_Prelim_P2_Ans

1 AHS 2021 Bio Paper 2 Prelim Exam Answers 1 (a) (i) (ii) B E 1 1 (b) Water/ urea/ glucose/ amino acids/ named ion e.g. Na+ 1 (c) H; Cells are constantly carrying out aerobic respiration thus the concentration of oxygen is low and oxygen will diffuse into the cells. 1 1 (d) Blood flows through a partially permeable dialysis tubing bathed in dialysis fluid; The dialysis fluid contains no urea, to ensure that urea will diffuse out of the blood into the fluid; Fluid contains useful substances like glucose/ amino acids/ salts (any two excluding water, which cannot be described using “concentration”) at concentrations similar to those of a healthy person, to prevent these from diffusing out of the blood; While excess salts and water move out by diffusion and osmosis respectively; Molecules like proteins, platelets and blood cells (any two) are too large to diffuse through the dialysis tubing; (any 4, but must address both parts of the qtn) 1 1 1 1 1 2 (a) (i) letter on Fig. 2.1 name of blood vessel oxygenated or deoxygenated blood D pulmonary vein oxygenated E aorta oxygenated 1,1 1,1 (ii) Has valves; To prevent backflow such that blood flows in one direction back to the heart; OR Has a large lumen relative to the diameter of the entire vessel; To reduce resistance to blood flow; OR Less elastic/muscular walls (than arteries); Enables vein to be squeezed by (surrounding skeletal) muscles to push the blood along 1 1 1 1 1 1 (b) (i) Percentage change = (135 – 181) / 181 x 100% = - 25.4% (3 s.f.) 1 1 (ii) Blood glucose conc. above the norm stimulated the islets of Langerhans in the pancreas; 1

2 Which released more insulin into the bloodstream; Stimulating the conversion of excess glucose into glycogen in the liver 1 1 3 (a) (i) Guard cells 1 (ii) Carbon dioxide diffuses through the stomata; into the intercellular air spaces; Dissolves in the thin film of moisture on the (spongy/palisade) mesophyll cells; Diffuses into chloroplast of mesophyll cell; 1 1 1 1 (b) (i) Carbon dioxide + Water Glucose + Oxygen 1 (ii) Accept between 0600 to 0624 1 (iii) Carbon dioxide concentration/ temperature/ concentration of chlorophyll within the plant 1 (iv) Rate of aerobic respiration was equal to the rate of photosynthesis; OR Any carbon dioxide produced during aerobic respiration was taken up by the plant for photosynthesis 1 (v) So that rate of photosynthesis is greater than rate of respiration/ glucose produced by the plant is not all used up in respiration; This ensures that there is surplus glucose/ food to be used to build new protoplasm/ some specific fate of glucose contributing to increase in mass described 1 1 4 (a) (i) Movement of sucrose and amino a