A-LevelBiologyGas exchangeMay/June 2024Paper 1 Q311 Mark
In the lungs, movement of dissolved carbon dioxide out of the capillaries occurs in one of two ways: • by diffusion through the endothelial cells of the capillaries • by leakage through pores in the endothelial cells of the capillaries. What is the minimum number of times that a carbon dioxide molecule that has been transported to the lungs in a red blood cell must cross a cell surface membrane to reach an air space in an alveolus?
A2
B3
C4
D5
✓ Correct Answer
The correct answer is B: 3
📋 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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