Diffusion - GCSE Biology Definition

What is diffusion?

In GCSE biology, diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. This movement is said to occur down a concentration gradient. When particles move by diffusion, the process continues until they are evenly distributed.

Diffusion can involve particles of a gas or particles in a solution. It is passive, meaning that it does not require energy to take place.

Diffusion can take place across cell membranes in living organisms, e.g. oxygen diffuses into the blood during gas exchange, and urea diffuses out of the blood during excretion.