Which feature of the alveoli is the most important adaptation for efficient gaseous exchange?
Correct answer: B. Their walls, one cell thick, giving an enormous surface area with a dense capillary network
- A. Their supporting rings of cartilage
- B. Their walls, one cell thick, giving an enormous surface area with a dense capillary network
- C. The cilia lining their inner surface
- D. The mucus that coats them
Explanation
Around 300 million alveoli give a surface of roughly 70 square metres, and a wall a single cell thick lying against an equally thin capillary means oxygen diffuses across a distance well under a micrometre. Continual blood flow and ventilation keep the diffusion gradient steep. Alveoli contain no cartilage or cilia, and a coat of mucus would in fact lengthen the diffusion path.
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About Gaseous Exchange in Lungs
Gaseous exchange in the lungs occurs across the thin, moist alveolar and capillary surfaces, where oxygen and carbon dioxide diffuse down partial pressure gradients. The topic covers alveolar adaptations, ventilation, the role of haemoglobin in oxygen transport, carbon dioxide carriage, and the difference between external gas exchange and cellular respiration.
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