Diffusion vs Active transport: what's the difference?
GCSE Biology
Two ways substances cross cell membranes — one passive, one requiring energy.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Diffusion vs Active transport — side by side
| Diffusion | Active transport | |
|---|---|---|
| Energy (ATP) needed? | No (passive) | Yes (requires respiration/ATP) |
| Direction | High → low concentration (down the gradient) | Low → high concentration (against the gradient) |
| Carrier proteins | Not needed (facilitated diffusion may use channels) | Required |
| Example | Oxygen into cells | Mineral ions into root hair cells |
Exam tip — how to tell them apart: Active transport goes AGAINST the gradient, so it needs energy from respiration — diffusion goes down the gradient for free.
Common trap: Because active transport needs ATP, cells doing lots of it (e.g. root hair cells) have many mitochondria — a common exam link.
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