Active Transport

This lesson covers active transport — the process by which cells move substances against a concentration gradient — as required by the AQA GCSE Combined Science Trilogy specification (8464). You need to understand the definition, how it differs from diffusion and osmosis, and be able to describe examples of active transport in living organisms.

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What Is Active Transport?

Active transport is the movement of particles from an area of lower concentration to an area of higher concentration — i.e. against the concentration gradient.

Key features:

• Active transport moves substances up (against) the concentration gradient — from low to high concentration.
• It requires energy from cellular respiration (unlike diffusion and osmosis, which are passive).
• The energy is used to power carrier proteins (transport proteins) in the cell membrane.
• Active transport allows cells to absorb substances even when the concentration inside the cell is already higher than outside.

$\text{Active transport: LOW concentration} \xrightarrow{\text{energy required}} \text{HIGH concentration}$Active transport: LOW concentrationenergy required​HIGH concentration

Exam Tip: Active transport is the opposite of diffusion in terms of direction. Diffusion goes from high to low (passive, no energy); active transport goes from low to high (active, requires energy).

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