How the Body Defends Itself Against Pathogens
Learn how the human body uses physical barriers, white blood cells, antibodies and antitoxins to defend itself against pathogens for AQA GCSE Biology.
The human body defends itself against pathogens using non-specific barriers that stop them entering and the immune system, which destroys pathogens that enter the body. Pathogens are microorganisms that cause infectious disease, including bacteria, viruses, fungi and protists.
Non-specific defence systems
These defences work against many different pathogens:
- Skin: forms a physical barrier that prevents pathogens entering the body.
- Nose: contains hairs and mucus that trap particles and pathogens before they reach the lungs.
- Trachea and bronchi: produce mucus that traps pathogens. Ciliated cells have tiny hair-like structures called cilia, which move the mucus towards the throat so it can be swallowed.
- Stomach: produces hydrochloric acid, which kills many pathogens that have been swallowed.
The immune system
If pathogens enter the body, white blood cells help to destroy them in three main ways:
- Phagocytosis: some white blood cells engulf and digest pathogens.
- Antibody production: white blood cells produce antibodies that bind to specific antigens on a pathogen. An antigen is a molecule on the pathogen’s surface. Each antibody has a complementary shape and is specific to one antigen.
- Antitoxin production: white blood cells produce antitoxins that neutralise toxins released by bacteria.
Example: a second infection
After an infection, some white blood cells remain as memory cells. If the same pathogen enters again, the immune system produces the correct antibodies more quickly. This rapid response can destroy the pathogen before the person becomes ill. Vaccination uses this principle by introducing dead or inactive forms of a pathogen to stimulate antibody production.
Common exam mistake
Do not say that antibiotics kill all pathogens. Antibiotics can kill infective bacteria, but they cannot kill viruses. Painkillers only treat symptoms; they do not kill pathogens.
Scope assumed: AQA GCSE Biology 8461, Higher tier. The defence-system content explained here is also assessed at Foundation tier and is not biology-only content.
