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Biology Paper 1 · B3 · Lesson 3.6

The body’s first defences

How skin, airways and stomach acid stop pathogens.

Key ideas1 of 3

Skin and the nose

Skin is a physical barrier. A blood clot seals a cut and reduces pathogen entry. In the nose, hairs and mucus trap particles, including pathogens.

Pathogens above a continuous row of skin cells cannot easily pass through intact skin.

These defences work against many different pathogens: they are non-specific.

Next: White blood cells and immunity →
Topic resources and sources

Daily 5 · Exam practice · Download the A4 revision sheet

Core content is shared by Foundation and Higher Tier. Challenge questions ask you to explain and apply it.

AQA Combined Science Trilogy specification · 4.3.1.6. Notes, questions and diagrams are original teaching material.

Rose leaf: LiquidGhoul / Wikimedia Commons, public domain. Mosquito: CDC / Jim Gathany, PHIL 5814, public domain. This photograph shows a vector species; it does not establish that this individual carries malaria.