2019 GCE O Level Bio Suggested Answer.

2019 TYS answer- Pure Biology Paper 1 1 B 11 D 21 C 31 C 2 D 12 B 22 D 32 C 3 C 13 B 23 B 33 A 4 B 14 C 24 D 34 D 5 D 15 D 25 D 35 D 6 B 16 A 26 A 36 D 7 B 17 C 27 D 37 D 8 C 18 C 28 D 38 A 9 B 19 C 29 A 39 B 10 A 20 D 30 A 40 C 1 (a)(i) Identify A is cell membrane. [1] State function A partially permeable membrane that controls the substances entering and leaving the cell. [1] 2 (ii) Identify B is ribosome. [1] State function Needed to synthesize proteins in the cell. [1] 2 (b) Suggest why (include explanation) Liver cells carry out many metabolic reactions that require energy. [1] The high number of mitochondria provides a higher amount of energy, released during aerobic respiration, to carry out these reactions. [1] 2 (c) State Plant cell has cell wall. [1] Plant cell has chloroplasts. [1] Plant cell has a large central vacuole. [1] (any 2) 2 (d) Suggest purpose Microvilli increases surface area to volume ratio [1] to increase rate of absorption of digested food. [1] 2

2 (a) Identify chambers A and B are the atria. C is the right ventricle. D is the left ventricle. [1] Explain why different thickness D has the thickest wall, 12mm, to pump the blood at high pressure, out of aorta to the rest of body. [1] C has a thinner wall, 5mm, than D as C pumps blood to the lungs, which is nearer to the heart [1] A and B have thinnest walls of 3mm as they only needs to force blood into the ventricles. [1] 4 (b) Suggest effects The hole cause mixing of the oxygenated and deoxygenated blood.[1] This results in less oxygen in blood being transported around the body [1] 2 (c) State Diet high in saturated fats and cholesterol/ stress/ smoking (any 1) 1 3 (a) Explain - As 1 has a higher water potential than 2, water leaves 1 (xylem vessel) and enters 2 (spongy mesophyll cell) by osmosis. - Water leaves 2 (spongy mesophyll cell) to form a thin film of moisture around the cell. - Water from the thin film of moisture evaporates forming water vapour. - Water vapour accumulates in 3 (intercellular air spaces). - As the concentration of water vapour in 3 is higher than at 5 (surrounding atmosphere), water vapour diffuses out of leaf through 4 ( stomata ) 5 (b) Identify J is the upper epidermal cell. [1] Explain Allows light to penetrate through into the photosynthesizing cells.[1] Identify K is the palisade mesophyll cell. [1] Explain Adaptation either one : - It has many chloroplasts containing chlorophyll to absorb light energy and convert it to chemical energy during photosynthesis. [1] - It is long and cylindrical to maximize sunlight absorption. [1] 4

(c) Explain When stomata are open, more carbon dioxide can diffuse into the leaf which is used for photosynthesis.[1] Oxygen produced at end of photosynthesis can also diffuse out of stomata. [1] Water vapour can diffuse out, incre