VS 2022 O Level Pure Biology P1+2 MS w Feedback

2022 / 6093 Biology Paper 2 Answer Scheme Section A Qn No Answer Mark Feedback 1(a) Haemoglobin pigment in RBC binds to oxygen to transport oxygen in the form of oxyhaemoglobin around the body. RBC has no nucleus - to ensure that there is more room for haemoglobin, maximising the amount of oxygen transported RBC is also biconcave - to increase the surface area to volume ratio of the cell to ensure oxygen can diffuse in and out of cell at a higher rate. 1 1 1 This question was generally well answered by all candidates with good linking of a structure to its correct function. Weaker responses referred to haemoglobin ‘transporting’ oxygen rather than binding to oxygen or referred to the cells as being ‘concave’ rather than biconcave. The lack of a nucleus was also often linked to providing more room for oxygen, rather than more room for haemoglobin. 1(b)(i) Sugges t: The person is likely to feel fatigued or breathless easily. Explain : As the person has a lower oxygen saturation of blood than normal, the m uscle cells may not receive enough oxygen for aerobic respiration to release energy. Thus, muscle cells may also undergo anaerobic respiration and the person will feel fatigued or breathless with continued physical activity. 1 1 1 Most responses correctly described how breathing or heart rate would be affected or described tiredness. Many went on to explain that less oxygen would be delivered to the muscles or cells for aerobic respiration. Stronger responses suggested the need for anaerobic respiration. Weaker responses gave a more generalised description of less oxygen delivered to the ‘body’, or just referred to ‘respiration’ without specifying aerobic respiration. The term ‘cellular respiration’ was often used without reference to ‘aerobic’ or ‘anaerobic’. Some also tried to explain how walking up stairs would alter the reading on the oximeter.

1(b)(ii) Pulmonary vein It transport blood directly from lungs right after gaseous exchange has occurred, thus, is highest in oxygen concentration. 1 1 Most candidates answered this well and could justify their choice. Good answers were often succinct. Some candidates mistook the pulmonary artery for the pulmonary vein. 1(c) Carbon dioxide: transported from body cells to be excreted at the lungs during exhalation. White blood cells/ lymphocytes/ phagocytes/ antibodies 1 1 The reason for transport of carbon dioxide was not well expressed by some candidates who did not mention the lungs, excretion, or exhalation. 2(a)(i) palisade mesophyll 1 2(a)(ii) vacuole 1 2(a)(iii) nucleus/ mitochondrion/ Golgi apparatus/ endoplasmic reticulum/ ribosome 1 2(b) Suggest: Chloroplasts would migrate towards the top of the cell , and pack closely together Explain: to maximise absorption of light by chlorophyll in low light intensity which is a condition for light-dependent stage of photosynthesis to occur 1 1 1 Almost all candidates understood the need for light energy to be absorbed by chlorophyll. Most went on to correctly relate this to photosynthesis. Weaker responses mistakenly thought that chloroplasts would migrate to the top of the leaf or to the epidermis, r ather than within the cell, or that they would spread out so as not to overlap each other.

2(c) Water moves from xylem to adjacent cells and into the palisade mesophyll cells in the leaf by osmosis; Down a water potential gradient , through the partially permeable cell membrane; Carbon dioxide diffuses into the intercellular air spaces, through the stomata; a down concentration gradient; Carbon dioxide dissolves in the thin film of water on the surface of mesophyll cells; Before diffusing into the cytoplasm of the mesophyll cells d own a concentration gradient; 1 1 1 3(a) long, pendulous filament; anthers protrude out of flower; 1 1 Focus your answer on stamen only 3(b)(i) Carbon Hydrogen Oxygen 1 Reject: Nitrogen (only found in proteins) 3(b)(ii) 1

White flour generally contains less indigestible carbohydrate than brown flour.( trend) WRF has 2.2g less than BRF (manipulate data) WWF has 8g less than BWF White flour generally contains less fat than brown flour. WRF has 1.4g less than BRF WWF has 1.5g less than BWF 1 This question proved challenging for some candidates. Most candidates had the right idea but did not give a clearly stated difference between named types of flour, instead relying on lists of quoted figures, expecting the figures to indicate ‘less’ or ‘more’ without being stated. 3(b)(iii) Add water to the flour, and mix. Decant mixture, and use the solution for the protein test. To 2cm 3 of sample, add 2 cm 3 of sodium hydroxide solution. Add copper(II) sulfate solution dropwise, shaking after every drop. Sample turns violet if proteins are present, and remains blue if proteins are absent. 1 1 The test and positive colour were well known. Only occasionally was Benedict’s reagent named and even then, the correct positive colour for protein was commonly described. A few candidates mixed up the tests and suggested heating Biuret reagent. 3(c) Decrease in size and number = decrease in total surface area to volume ratio for absorption of digested food substances Reduced absorption of digested food substances such as glucose and amino acids into bloodstream, and fats into lacteals More digested food substances may be egested due to impaired absorption → leading to nutrient deficiencies (affects peristalsis/ absorption) 1 1 1 Most candidates were able to state that absorption would be reduced as the surface area for absorption was reduced. Only the stronger responses gave further detail, such as stating specific nutrients that would be absorbed (into the bloodstream or lacteals) or egested without absorption.

4(a)(i) 2 This was generally answered well by most candidates. The most common error was to show the blood in the hepatic portal vein flowing away from the liver. 4(a)(ii) hepatic vein 1 4(b)(i) Population size in each area may differ significantly thus using the total number of men as compared to ratio/percentage will result in unreliable/inaccurate results. 1 Several candidates correctly identified that the population sizes could be different. Weaker responses made suggestions about the ‘figures being too large to fit on a graph’. 4(b)(ii) A: number of cases increased sharply from 1960 to 1978, from 38 per 100 000 men to 64 per 100 000 men then decreases sharply from 1978 to 2000 to 36 per 100 000 men B: number of cases increased continuously from 1960 to 2000 from 7 per 100 000 men to 27 per 100 000 men 1 1 1 Many candidates tried to support comparisons with data but several missed that the figures were ‘per 100 000’, or attempted to manipulate the figures incorrectly (e.g. 500 000 cases in B in 1960).

4(b)(iii) Better