Active transport

Structure and functions in living organisms · Movement of substances into and out of cells · note 3 of 5

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Active transportSpec 2.15

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 them. For example, root hair cells absorb 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 IGCSE Biology (4BI1) specification · Updated October 2026

Frequently asked questions

How does osmosis differ from diffusion?

Osmosis is a special type of diffusion that involves only water moving through a partially permeable membrane. Diffusion is the net movement of any particles, such as oxygen or carbon dioxide, from a higher to a lower concentration. In osmosis, water moves from a dilute solution to a more concentrated solution. Neither process needs energy from respiration.

Why does osmosis not require energy?

Osmosis does not require energy because it is a passive process. Water simply diffuses from a dilute solution to a more concentrated solution through a partially permeable membrane, so no energy from respiration is used. Only active transport, which moves substances against a concentration gradient, needs energy from respiration.

Why is active transport needed in plant roots?

Active transport is needed in plant roots because root hair cells often contain a higher concentration of mineral ions than the soil. Diffusion would move ions out of the cell, so the cells must use energy from respiration to move ions in against the concentration gradient. This lets plants take in ions that are in short supply.

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