A-LevelBiologyGas exchange9700/22 · May/June 2021 · Q410 Marks
A person who is exposed to tobacco smoke is at greater risk of lung cancer and chronic obstructive pulmonary disease (COPD). Many people with COPD have both chronic bronchitis and emphysema. These diseases cause changes in the gas exchange system. For example, changes occur in the total lung surface area to volume ratio (SA:V).
- (a)Tar in tobacco smoke has a number of effects on the cells lining the gas exchange system. State the main effects of tar on the cells lining the gas exchange system that are related to lung cancer and to chronic bronchitis. lung cancer chronic bronchitis[3]
- (b)A student investigated the effect of SA:V on diffusion. Agar was prepared with Universal Indicator solution and sodium hydroxide solution. The agar was coloured blue. Three cubes, A, B, and C, were cut from a solid block of blue agar. Each cube was a different size. Universal Indicator solution changes to a red colour in the presence of acid. The student prepared Table 4.1 to show the sizes and SA:V of each cube. Table 4.1 cube length of each side/cm total surface area/cm² volume/ SA:V A 1 6 1 6:1 B 2 24 8 3:1 C 3 2:1 Complete Table 4.1 by: • writing the correct units for volume • calculating the total surface area, and volume, of cube С.[2]
- (c)Cubes A, B and C were placed in a small beaker. At time 0 seconds, dilute hydrochloric acid was added to the beaker to cover the cubes. The student timed how long it took for each cube to change colour completely. Complete Fig. 4.1 to show the results that were obtained. shortest time to change colour completely cube longest time to change colour completely cube cube Fig. 4.1[1]
- (d)Some people with emphysema may be offered lung volume reduction surgery (LVRS), in which diseased lung tissue is surgically removed. One expected outcome of the surgery is an improvement in total lung surface area to volume ratio (total lung SA:V). Suggest why there is an improvement in total lung SA:V after the surgery has been carried out.[2]
- (e)In humans, blood that becomes oxygenated in the lungs reaches body tissues without coming into contact with blood that is deoxygenated. Explain how the blood that becomes oxygenated in the lungs is kept separate from blood that is deoxygenated.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- [3] any three from lung cancer to max 2 (tar) is a carcinogen ; acts as mutagen / causes mutations / described; I mutant cells e.g. causes changes to sequence of, bases / nucleotides, in DNA detail; I uncontrolled mitosis e.g. tumour suppressor genes switched off protooncogenes to oncogenes / oncogenes switched on (cell cycle) checkpoints fail to function AW cell moves from, G0 / inactive state of cell cycle, to G1 phase (for mitosis) no programmed death / AW chronic bronchitis to max 2 (tar) paralyses / destroys / damages / AW, cilia ; I weakens cilia A damage to ciliated (epithelial) cells consequence to cilia action; must be related to mp1 e.g. cilia do not, waft away / AW, mucus loss of synchronous rhythm of cilia (tar causes), goblet cells / mucous glands, to, increase in size / enlarge / AW ; A (tar / accumulation of mucus, causes) inflammation more / excess, mucus produced (by, goblet/mucous gland cells) ; I mucus accumulates
- [2] correct units for volume cm³ ; SA and volume calculation (SA) = 54 (V) = 27 ;
- [1] A→B→C; A 6:1 3:1 2:1 A 1→2→3
- [2] any two from (in emphysema) alveolar walls break down / alveoli burst, to, produce one large air sac / give a lower SA:V or diseased, tissue / areas / alveoli, has lower SA:V (than healthy tissue); removed tissue has (higher proportion of), large air sacs / diseased alveoli ; remaining tissue has, healthy / undamaged / functional / only, alveoli; AW A volume reduced and functional surface area of lung remains the same A remaining tissue has higher functional surface area (than before surgery)
- [2] any two from 1 only oxygenated blood passes through left side of heart ora or oxygenated blood in left side and deoxygenated blood in right side of heart; 2 septum in heart separates (oxygenated and deoxygenated) blood ; 3 oxygenated blood is in pulmonary, venules / veins and deoxygenated blood is in, pulmonary arteries / arterioles ; 4 (because mixing prevented by) double circulation / double circulatory system / pulmonary and systemic circulations ;
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