2018 GCE O Level Bio Suggested Answer

2018 GCE O Level Biology Suggested Answer Paper 1 1 2 3 4 5 6 7 8 9 10 A A B B C D C A B A 11 12 13 14 15 16 17 18 19 20 C B C D A B C C B D 21 22 23 24 25 26 27 28 29 30 B D A D C C D B B A 31 32 33 34 35 36 37 38 39 40 C D A C D A C B D D Paper 2 (Section A) 1 (a) (i) State Chromosome 1 6 (ii) State Stage 3: Metaphase Stage 4: Anaphase 1 1 (b) (i) State Plant 2 1 (ii) State Plant 1: AA Plant 3: aa 1 1 2 (a) (i) State any 3 functions 1. Liver converts excess glucose to glycogen when stimulated by insulin 2. Produce bile 3. Stores iron 4. Deaminates excess amino acids 5. Detoxification of harmful substances into harmless substances 3 10

6. Liver converts stored glycogen to glucose when stimulated by glucagon (ii) State letter C 1 (iii) State Name: Bile Describe Function: Emulsifies large fat droplets into smaller fat droplets to increase surface area to volume ratio for faster rate digestion by lipase. 1 1 (b) (i) State 40 ◦C 1 (ii) Suggest The enzyme, rennin, had denatured and therefore lost its 3D active site so it could not bind to milk and cause it to clot. Therefore it did not form lumps. 1 (c) Suggest When it forms lumps, the flow of milk through the alimentary canal is slower and this increases the time for complete digestion and maximum absorption of nutrients for the developing young cow. 1 1 3 (a) (i) State 3 minutes 1 5 (ii) Describe relationship As temperature increases, the time taken for human blood to clot decreases. The graph shows that as temperature increases from 15 ◦C to 35 ◦C, the time taken for human blood to clot decreases from 24 minutes to 2.5 minutes. 1 1

(b) State 2 functions 1. Seals the wound to prevent excessive bleeding/ excessive loss of blood. 2. It prevents foreign particles (bacteria and virus) from entering the bloodstream and causing an infection. 1 1 4 (a) Describe adaptation 1. The wall of the alveolus is one cell thick. This provides a shorter diffusion distance for gases ensuring a faster rate of diffusion. 2. A thin film of moisture covers the inner surface of the alveolus and allows oxygen to dissolve in it for efficient diffusion of oxygen across alveolar wall. 3. The wall of the alveolus is supplied with a blood capillary that helps maintain the concentration gradient of gases for efficient diffusion with the continuous flow of blood. 1 1 1 11 (b) Suggest effect Carbon dioxide will not be fully removed from tissues and excreted from the lungs during exhalation. Explain effect Carbonic anhydrase, an enzyme present in the red blood cell, catalyses a reversible reaction in the formation of carbonic acid from carbon dioxide and water. Carbonic acid then dissociates into hydrogen ions and bicarbonate ions, transported in blood to the lungs. Hence, low levels of carbonic anhydrases indicates that less carbon dio