A-LevelBiologyGas exchangeMay/June 2019Paper 1 Q331 Mark
The surface tension of the layer of liquid lining the alveoli tends to pull the walls inwards so alveoli could collapse. Which statements could explain how this is prevented? 1 Alveolar fluid is moved around by cilia. 2 Elastic fibres keep the alveoli open. 3 Epithelial cells secrete a chemical that reduces the cohesion in water.
A1 and 2
B1 and 3
C2 and 3
D3 only
✓ Correct Answer
The correct answer is D: 3 only
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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