IGCSE Biology glossary
Alveolar wall
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Definition
The thin wall of an alveolus, only one cell thick, through which gas exchange occurs between the air in the alveolus and the blood in surrounding capillaries. Its thinness provides a short diffusion distance for oxygen and carbon dioxide.
What to include in an exam answer
In gas exchange adaptation questions, always state that the alveolar wall and capillary wall together are only two cells thick, giving a very short diffusion distance.
Example in context
Explain how the thin walls of the alveoli are important for gas exchange (2 marks): The alveolar wall is one cell thick, which provides a very short diffusion distance. This allows oxygen and carbon dioxide to diffuse rapidly between the air in the alveolus and the blood in the capillaries.
Related syllabus topic
Gas exchange in humans