Grade 12 · Biology
Gas exchange & transport
Why it matters
Oxygen, carbon dioxide and control.
Advanced20m readingPrerequisite: Breathing mechanics
How does gas exchange work in the lungs?
Short answer
Gas exchange occurs in the alveoli, tiny air sacs surrounded by capillaries. Oxygen diffuses from the high concentration in inhaled air across the thin alveolar wall into the blood, while carbon dioxide diffuses the opposite way to be exhaled. Diffusion is driven by partial-pressure gradients, and the alveoli’s huge surface area makes it efficient.
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Frequently asked questions
- Why are alveoli well suited to gas exchange?
- They provide a large, thin, moist surface area richly supplied with capillaries, so gases diffuse quickly.
- What drives the movement of gases?
- Differences in partial pressure: each gas diffuses from where it is more concentrated to where it is less concentrated.