Body defencesSpec B10.1.4
In short
The body's defences against pathogens include barriers that keep them out and cells that destroy those that get in. The skin is a tough barrier, nose hairs and mucus trap pathogens, and stomach acid kills most swallowed pathogens. White blood cells destroy pathogens inside the body by ingesting them or by making antibodies.
The body has defences that stop pathogens getting in, and others that destroy the ones that do get in.
| Defence | How it protects the body |
|---|---|
| Skin | Forms a tough barrier that stops pathogens entering the body. |
| Hairs in the nose | Trap dust and pathogens in the air that is breathed in. |
| Mucus | Sticky liquid in the nose and airways that traps pathogens so they can be removed. |
| Stomach acid | Kills most pathogens that are swallowed in food and drink. |
| White blood cells | Destroy pathogens that get inside the body, for example by ingesting them (phagocytes) or by making antibodies (lymphocytes). |
Common mistake:
Hairs and mucus do not kill pathogens. They trap them. Stomach acid and white blood cells are the defences that kill or destroy pathogens.
Written and checked against the Cambridge IGCSE Combined Science (0653) specification · Updated October 2026