Active Transport

This lesson covers active transport — the third transport mechanism across cell membranes — as required by the Edexcel GCSE Biology specification (1BI0), Topic 1: Key Concepts in Biology. You need to understand how active transport differs from diffusion and osmosis, know key examples, and be able to compare all three processes.

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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.

Key Characteristics

• Active transport moves substances against the concentration gradient (from low → high concentration).
• It requires energy from cellular respiration (the energy currency is ATP — adenosine triphosphate).
• It uses carrier proteins (specific transport proteins) embedded in the cell membrane.
• It is an active process — the cell must expend metabolic energy.

Exam Tip: The key difference from diffusion is the direction. Diffusion goes down the concentration gradient (high → low) passively. Active transport goes against the concentration gradient (low → high) and requires energy. If a question says substances move "against the concentration gradient", the answer is always active transport.

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