Transport in Cells - AQA GCSE Biology Revision

Topic overview

What you need to know

Transport in Cells is a key part of GCSE Biology. Connect structures to their functions and explain biological processes as clear causal sequences. The net movement of particles from an area of higher concentration to an area of lower concentration. It is a passive process (no energy required). The movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane. The movement of substances from a lower concentration to a higher concentration (against the concentration gradient), requiring energy from respiration.

Exam tip

Use precise scientific vocabulary and make each link in an explanation explicit.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

Diffusion: The net movement of particles from an area of higher concentration to an area of lower concentration. It is a passive process (no energy required).
Osmosis: The movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane.
Active Transport: The movement of substances from a lower concentration to a higher concentration (against the concentration gradient), requiring energy from respiration.
Concentration Gradient: The difference in concentration between two areas. Substances move down their concentration gradient in diffusion.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

Partially Permeable Membrane: A membrane that allows some molecules through but not others, based on size.
Turgid: A plant cell that is firm and swollen because it has absorbed water by osmosis and the vacuole pushes against the cell wall.
Plasmolysed: A plant cell that has lost water by osmosis, causing the cell membrane to pull away from the cell wall.
Surface Area to Volume Ratio: Smaller organisms have a larger SA:V ratio, making diffusion more efficient. Larger organisms need transport systems.

Core knowledge

Key facts for Transport in Cells

8 essentials

Diffusion

The net movement of particles from an area of higher concentration to an area of lower concentration. It is a passive process (no energy required).

Osmosis

The movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane.

Active Transport

The movement of substances from a lower concentration to a higher concentration (against the concentration gradient), requiring energy from respiration.

Concentration Gradient

The difference in concentration between two areas. Substances move down their concentration gradient in diffusion.

Partially Permeable Membrane

A membrane that allows some molecules through but not others, based on size.

Turgid

A plant cell that is firm and swollen because it has absorbed water by osmosis and the vacuole pushes against the cell wall.

Plasmolysed

A plant cell that has lost water by osmosis, causing the cell membrane to pull away from the cell wall.

Surface Area to Volume Ratio

Smaller organisms have a larger SA:V ratio, making diffusion more efficient. Larger organisms need transport systems.

Active recall

Close the notes and answer these

1.Without looking, explain diffusion and give one example or consequence.
2.Without looking, explain osmosis and give one example or consequence.
3.Without looking, explain active transport and give one example or consequence.
4.Without looking, explain concentration gradient and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

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