Active Transport vs Diffusion: What Is the Difference?
Learn what active transport is, why it needs energy, and how it differs from diffusion in GCSE Biology, with clear definitions and examples.
Active transport moves substances from a more dilute solution to a more concentrated solution, using energy from respiration. Diffusion moves particles from an area of higher concentration to an area of lower concentration and does not require energy.
What is active transport?
Active transport moves substances against the concentration gradient. A concentration gradient is the difference in concentration between two areas.
Because the particles are moving in the opposite direction to their natural movement, the cell must supply energy from respiration.
Examples include:
- root hair cells absorbing mineral ions from very dilute solutions in the soil
- cells in the small intestine absorbing sugar molecules when their concentration is lower in the gut than in the blood
How is it different from diffusion?
| Active transport | Diffusion |
|---|---|
| Moves substances from a lower concentration to a higher concentration | Moves particles from a higher concentration to a lower concentration |
| Moves against the concentration gradient | Moves down the concentration gradient |
| Requires energy from respiration | Does not require energy |
| Only occurs across cell membranes | Can occur with or without a cell membrane |
Worked example
Suppose the soil contains a lower concentration of mineral ions than the inside of a root hair cell. The ions cannot enter the cell by diffusion because diffusion would move them in the opposite direction.
Instead, the root hair cell uses active transport. Energy released by respiration allows mineral ions to move from the dilute soil solution into the more concentrated contents of the cell.
Common exam mistake
Do not say that active transport moves substances “from high concentration to low concentration”. That describes diffusion. For full understanding, link active transport to both movement against the concentration gradient and energy from respiration.
This content applies to both Foundation and Higher tiers and is shared with AQA Combined Science.
