The immune system and vaccination · GCSE Biology

The body's first defences

Skin is a physical barrier and makes antimicrobial secretions; scabs seal cuts.
Hairs and mucus in the nose trap particles that could contain pathogens.
The trachea and bronchi make mucus that traps pathogens, and cilia move the mucus up to the throat to be swallowed.
The stomach makes hydrochloric acid, which kills pathogens in food and drink.

If a pathogen gets into the body, the immune system tries to destroy it. White blood cells are the key.
Phagocytosis: some white blood cells engulf and digest pathogens.
Some white blood cells produce antibodies, which bind to specific antigens on a pathogen and help destroy it.
Some white blood cells produce antitoxins, which neutralise toxins made by bacteria.

Antigens are proteins on the surface of a pathogen. Each pathogen has its own antigens.
Antibodies are specific: each type fits only one antigen.
The first time a pathogen enters, it takes time to make enough antibodies, so you may become ill.
Memory cells then stay in the blood. If the same pathogen returns, antibodies are made quickly and in large numbers, so you are immune.

A vaccine contains small amounts of a dead or inactive form of a pathogen.
It stimulates white blood cells to produce antibodies, as if the person were infected, but without making them ill.
If the same live pathogen enters later, white blood cells respond quickly to make the right antibodies, preventing infection.
If a large proportion of the population is vaccinated, the pathogen cannot spread easily. This protects people who cannot be vaccinated (herd immunity).

Immune system: The body's defence system against pathogens, mainly white blood cells.
Phagocytosis: When a white blood cell engulfs and digests a pathogen.
Antigen: A protein on the surface of a pathogen that the immune system recognises.
Antibody: A protein made by white blood cells that binds to a specific antigen.
Antitoxin: A substance made by white blood cells that neutralises bacterial toxins.
Vaccination: Giving a dead or inactive form of a pathogen to make the body produce antibodies.
Immunity: Being able to respond quickly to a pathogen and destroy it before it causes illness.
Herd immunity: When so many people are vaccinated that a disease cannot spread easily, protecting the unvaccinated.
Cilia: Tiny hairs on cells lining the airways that move mucus.
Memory cells: White blood cells that remember an antigen and make antibodies quickly if it returns.