Differences in Inspired & Expired Air (Cambridge International IGCSE Biology)
Exam board Cambridge International · IGCSEUpdated 2026-08-28
Spec point —
11.1.4· nan
Differences in inspired & expired air
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Air that is inhaled, or breathed in, differs in its gas composition to air that is exhaled, or breathed out; this is due to the process of gas exchange that takes place in the alveoli
- Inhaled air can also be referred to as inspired air
- Exhaled air is also known as expired air
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Inhaled air is drawn from the surrounding atmosphere, and so its gas composition matches atmospheric levels
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During gas exchange in the alveoli oxygen enters the blood from the alveoli, and carbon dioxide and water vapour leave the blood and enter the alveoli
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This gas exchange process means that the gas composition of exhaled air differs to that of the air that was previously inhaled
- Inhaled air contains around 21 % oxygen and exhaled air contains around 16 % oxygen
- Inhaled air contains around 0.04 % carbon dioxide and exhaled air contains around 4 % carbon dioxide
- Inhaled air contains less water vapour than exhaled air
Composition of inhaled and exhaled air table
| Gas | Inspired air (%) | Expired air (%) |
|---|---|---|
| Oxygen | 21 | 16 |
| Carbon dioxide | 0.04 | 4 |
| Water vapour | 0.2 - 4 | 1 - 5 |
| Nitrogen | 78 | 78 |
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