IGCSE Biology glossary
Diffusion
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
The net movement of particles from a region of their higher concentration to a region of their lower concentration, down a concentration gradient, as a result of their random movement.
What to include in an exam answer
Examiners pay for 'net movement' and 'down a concentration gradient'. The phrase 'random movement' earns the third mark in full definitions. Common penalty: saying particles 'want to' spread out. Particles have no intention; keep the language passive.
Example in context
To explain gas exchange in a leaf: 'Carbon dioxide diffuses into the leaf from a region of its higher concentration outside to its lower concentration inside, down the concentration gradient.'
Related syllabus topic
Movement into & out of cells