Transport in Cells: Diffusion

This lesson covers diffusion as required by AQA GCSE Biology specification 4.1.3. You need to understand the process of diffusion, the factors that affect the rate of diffusion, and how diffusion is involved in the movement of substances into and out of cells, including examples in the human body and in plants.

---

What Is Diffusion?

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient. It occurs in liquids and gases because the particles are free to move randomly.

Diffusion is a passive process — it does not require energy from the cell (no ATP is needed). It occurs naturally because of the random movement of particles.

Key Definitions