Question Constellation Sign up for free AQA · GCSE · Biology · Higher
Alveolar Adaptations for Gas Exchange
Gas exchange happens in the alveoli in the lungs.
Describe three features of the alveoli that help maximise gas exchange.
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Marking points
- 1 Describes the large surface area or surface-area-to-volume ratio.
- 2 Describes the extensive capillary network or efficient blood supply.
- 3 States that the alveolar walls are thin or one cell thick.
Full-mark answer
Alveoli have a very large surface area, they are surrounded by a dense capillary network that gives a good blood supply, and their walls are thin—only one cell thick.
Why this answer loses marks
The alveoli have thin cell walls and are moist.
Thin cell walls is rejected and moisture is ignored; use credited alveolar-wall, surface-area and blood-supply features.