Active transport

Key concepts in biology · Transport in cells · note 3 of 5

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Active transportSpec 1.15

In short

Active transport is the movement of substances from a more dilute solution to a more concentrated solution, against a concentration gradient, using energy from respiration. It lets cells take in substances that are in short supply outside the cell. For example, root hair cells take in mineral ions from the soil even when the concentration inside the cell is higher.

Active transport is the movement of substances from a more dilute solution to a more concentrated solution, which is against a concentration gradient. It needs energy from respiration.

Active transport allows cells to take in substances they need even when they are in short supply outside the cell. For example, root hair cells take in mineral ions from the soil when the concentration of the ions is higher inside the cell than in the soil.

Three ways substances move into and out of cells
	What moves	Direction	Energy from respiration?
Diffusion	Particles, such as oxygen and carbon dioxide	High to low concentration	No
Osmosis	Water only, through a partially permeable membrane	Dilute to concentrated solution	No
Active transport	Substances such as mineral ions	Low to high concentration, against the gradient	Yes

Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

How does osmosis differ from diffusion?

Osmosis is the diffusion of water only, through a partially permeable membrane, from a dilute solution to a more concentrated solution. Diffusion is the net movement of any particles, such as oxygen or carbon dioxide, from a higher to a lower concentration. Both are passive processes, so neither needs energy from respiration.

Why does osmosis not require energy?

Osmosis does not require energy because it is a passive process. Water diffuses from a dilute solution to a more concentrated solution through a partially permeable membrane, so no energy from respiration is needed. Active transport is different: it moves substances against a concentration gradient, so it does need energy from respiration.

Why is active transport important in root hair cells?

Active transport lets root hair cells take in mineral ions from the soil even when the concentration of ions is higher inside the cell than in the soil. This movement is against the concentration gradient, so diffusion cannot do it. Active transport uses energy from respiration to move the ions into the cell.

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