VS 2019 O Level Pure Biology P1+2 MS w Feedback

2019 Biology 6093 Suggested Answers Paper 1 1 2 3 4 5 6 7 8 9 10 B D C B D B B C B A 11 12 13 14 15 16 17 18 19 20 D B B C D A C C C D 21 22 23 24 25 26 27 28 29 30 C D B D D A D D A A 31 32 33 34 35 36 37 38 39 40 C C A D D D D A B C Feedback - Paper 1

6 This question was challenging for many candidates. A large number of candidates selected option D. This indicates they did not realise that during osmosis, water molecules move in both directions through the membrane; although, in this case, the net flow is into the Visking tubing bag 10 A significant number of candidates chose either option C or option D. This shows that these candidates did not realise that given a supply of mineral ions, plants are capable of synthesising any other chemical that they require. Many did not appreciate that glucose is the initial chemical from which plants can manufacture both proteins and cellulose, or that the glucose also has to be respired to release energy for the plant’s use. 15 Many did not realise that both sides of the heart act together. 27 These candidates might have selected their answer on the basis of ‘identical’. They did not realise that no zygotes are present in asexual reproduction. Paper 2 Section A:

Q No Suggested Answers Marks Feedback 1(a)(i) cell membrane It is partially permeable membrane which controls the movement of substances into and out of the cell 1 1 Include the property of the membrane which enables it to carry out its function. Most candidates correctly identified A. Stronger performing candidates understood the idea of control over the entry and exit of substances. 1(a)(ii) ribosome synthesise proteins 1 1 Most candidates could identify B and its function. 1(b) detoxification/ secretion of important substances such as bile requires a larger amount of energy , hence, a large number of mitochondria is present to release the high amount of energy required. 1 1 The roles of both the liver and mitochondria were well known by almost all candidates. Weaker responses did not make the link between them. 1(c) 1. chloroplasts 2. cell wall 1 1 Almost all candidates could correctly identify the components of plant cells. 1(d) Microvilli is an extensive folding of the cell membrane which increases the surface area to volume ratio of the cell. These cells are found on the epithelium of the small intestines, which increases the rate of absorption of nutrients/ digested food. 1 1 Candidates knew that the microvilli increased surface area to volume ratio. Weaker responses referred to the increased absorption of ‘food’ rather than of ‘digested food’.

2(a) A and B - atrium C - right ventricle D - left ventricle Identify: Chambers A and B are the atria of the heart as they have the lowest mean wall thickness of 3 mm. Chamber C is the right ventricle with the mean wall thickness of 5 mm. Chamber D is the left ventricle as it has the highest mean thickness of 12 mm. Explain: Atrial wall is the thinnest (less muscle) as blood flows into the ventricles and does not require high pressure. The right ventricle pumps blood towards the lung s, requires a smaller pressure as the blood travels a shorter distance. The left ventricle has the thickest wall and pumps blood with most pressure as the blood needs to travel to the rest of the body. 1 1 1 1 Use data. The stronger responses correctly identified the four chambers and could relate their wall thickness to their function. A common misconception was that chambers A and B were on the right side of the heart (atrium and ventricle respectively), while C and D were on the left. Weaker responses did not describe the pumping of blood to the appropriate place and simply described it in terms of the flow or transport of blood. 2(b) The hole between the atria will l eads to mixing of; oxygenated and deoxygenated blood Blood entering the LV and eventually the rest of the body will contain significantly lesser oxygen than normal. Effects on the body: shortness of breath and fatigue. 1 1 The majority of candidates knew that a hole between the right and left atria would result in oxygenated and deoxygenated blood being mixed.

2(c) Atherosclerosis/ fatty diet/ sedentary lifestyle/ smoking 1 Almost all candidates could give a correct reason for the occlusion 3(a) 1. water molecules are entering the leaf via xylem due to transpiration pull 2. from xylem, water molecules diffuse into the spongy mesophyll cells via osmosis , down water potential gradient 3. excess water diffuses out to form a thin film of moisture will then 4. evaporate into the intercellular air spaces. 5. guard cells control the opening of the stomata 6. when stomata are widened, as the concentration of water vapour is higher in the intercellular air spaces compared to the environment, water vapour diffuses out of the leaf. 1 1 1 1 1 Direction from A to B stated clearly. Include processes and difference in concentration. The stronger responses used scientific terms correctly, differentiating between diffusion, osmosis, evaporation and concentration gradient . Weaker responses referred to water ‘dissolving’ in the layer on the surfaces of mesophyll cells or did not refer to water diffusing from the leaf as water vapour. 3(b) J is an upper epidermal cell Secretes waxy cuticle layer that provides a waterproof layer to prevent excessive water loss/ the cells are transparent, allowing sunlight to pass through for photosynthesis to take place K is a palisade mesophyll cell Contains a large number of chloroplasts to increase light absorption for higher rate of photosynthesis 1 1 1 1 Most candidates correctly identified cell J; stronger responses went on to describe its correct function. Weaker responses identified the cell as ‘epithelial’ or ‘cuticle’ cell, and its function as waterproofing. Cell K was identified correctly by most candidates and a correct adaptation was also seen. 3(c) During photosynthesis, plants convert the light energy to chemical energy . During the day, plants are actively photosynthesising due to the presence 1 Advantage to plants: Link back to photosynthesis Many candidates referred to the intake of carbon dioxide

of sunlight. Stomata stay open to allow gaseous exchang e to take place. Carbon dioxide (raw material) diffuses into the leaf through the stomata and dissolves in the moisture layer on the spongy mesophyll cells. Oxygen produced from photosynthesis can also diffuse out. Opening of stomata reduces the water potential in the leaf as water is lost through transpiration, and more water(raw material) will enter the leaf. The abundance of carbon dioxide and water allows the plant to photosynthesise effectively hence enabling optimal growth . 1 1 1 and