Active Transport — AQA GCSE Biology
Active transport moves substances against a concentration gradient, and it needs energy.
What is active transport?
Active transport is the movement of substances from a region of lower concentration to a region of higher concentration — that is, against the concentration gradient.
Because it works against the gradient, it requires energy released by respiration.
Examples
- Root hair cells absorb mineral ions (e.g. nitrate) from the soil, where they are in lower concentration than inside the cell.
- The small intestine absorbs glucose (and other nutrients) into the blood even when the concentration in the gut is lower, ensuring all the sugar is taken up.
Comparing the transport processes
| Process | Direction | Energy needed? |
|---|---|---|
| Diffusion | high → low (down gradient) | no (passive) |
| Osmosis | water, dilute → concentrated | no (passive) |
| Active transport | low → high (against gradient) | yes (from respiration) |
Exam tips
- Active transport goes against the concentration gradient and needs energy from respiration.
- Learn the two key examples: root hair cells (mineral ions) and the gut (glucose).
- Be able to contrast active transport with diffusion and osmosis in a table.
- Cells doing lots of active transport have many mitochondria to supply energy.