Everything on the GCSE Biology The Immune System & Body Defences poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Body Defences
The body has several non-specific barriers that stop pathogens entering or kill them before they can cause infection.
- Skin – a tough physical barrier.
- Nose hairs and mucus – trap pathogens in the air you breathe.
- Cilia in the trachea and bronchi – beat to waft mucus (with trapped pathogens) up towards the throat to be swallowed.
- Hydrochloric acid in the stomach – kills most pathogens swallowed in food or mucus.
- Tears – contain lysozyme, an enzyme that kills bacteria on the surface of the eye.
If pathogens get past these barriers, white blood cells carry out a targeted immune response.
Phagocytosis
A white blood cell called a phagocyte engulfs the pathogen and digests it with enzymes.
- The phagocyte moves towards the pathogen.
- It surrounds and engulfs the pathogen.
- Enzymes inside the cell break the pathogen down.
This response is non-specific – phagocytes destroy many types of pathogen.
Antibodies
A different type of white blood cell, the lymphocyte, produces antibodies that bind to specific antigens on the surface of a pathogen.
- The lymphocyte detects the pathogen's antigens.
- It produces antibodies with a complementary shape.
- The antibodies bind to the pathogen, clumping pathogens together and marking them for destruction by other white blood cells.
Each antibody is specific to one type of antigen, so this is part of the specific immune response.
Antitoxins
Some pathogens release toxins that damage body cells. Lymphocytes also produce antitoxins that bind to these toxins and neutralise them before they can cause harm.
- The lymphocyte detects a toxin.
- It produces antitoxins that bind to the toxin molecules.
- The neutralised toxins can no longer damage cells.