Biology / Unit 12 Bio 2727 short lesson, about 20 seconds
Surface-to-Volume Ratio Limits Size
Captions available
The idea
As a cell or organism grows larger, its surface-to-volume ratio falls, so diffusion can no longer supply its interior fast enough.
In practice
A single-celled amoeba relies on diffusion alone; a larger body evolves circulatory and respiratory systems instead.
Where people slip
The limit is diffusion distance, not cell number — a large body works around it through specialized transport.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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