Which feature of the alveoli makes gas exchange efficient?
Answer and explanation
Correct answer: A. The walls are one cell thick and surrounded by a dense capillary network
- Step 1: Fick's law: diffusion is fast when the surface area is large and the diffusion path is short.
- Step 2: Alveoli are thin-walled and richly supplied with capillaries, keeping a steep concentration gradient.
Answer
The walls are one cell thick and surrounded by a dense capillary network.
Why not the others: The walls are several cells thick to strengthen the surface: a thick barrier would slow diffusion. The alveoli have a small total surface area but a high blood pressure: the total surface area is large. The capillaries are far from the alveoli to allow time for exchange: a short diffusion distance is needed.
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