IGCSE Biology glossary
Alveoli
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
The tiny air sacs in the lungs where gas exchange takes place. Oxygen diffuses into the blood and carbon dioxide diffuses out.
What to include in an exam answer
Adaptation questions are the staple: large total surface area, thin walls (one cell thick. Short diffusion distance), good blood supply (maintains concentration gradient), moist lining. Tie every feature to HOW it speeds up diffusion, or the marks halve.
Example in context
Linking adaptation to function: 'The alveoli have a large surface area and walls one cell thick, so oxygen diffuses quickly into the blood over a short distance.'
Related syllabus topic
Gas exchange in humans