Health

5. A microscopic organism, including bacterium, virus, or fungus.
7. A process which renders to organism immunity to a specific disease by exposing the organism to an antigen to promote the production of antibodies to a particular antigen.

1. Microscopic living organisms, usually one-celled, that can be found everywhere. They can be dangerous or beneficial.
2. Specialised cells that help the immune system fight disease.
3. A small infectious agent that replicates only inside the living cells of other organisms.
4. A biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe.
6. Examples include molds, mildews, mushrooms, that are parasites on living organisms or that feed upon dead organic material.