group of unicellular eukaryotic organisms

Protozoa are microorganisms. They are single-celled heterotrophic eukaryotes, which eat bacteria and other food sources.

Giardia lamblia is a parasitic flagellate protozoan which causes 'beaver fever'.[1]

It is an old term, and the wider term protist is generally preferred today. However, 'protozoa' is often used for convenience, especially in junior education.[2] It is a convenient hold-all term, and most systems of taxonomy classify 'protozoa' into several different phyla.

The term is problematic because modern biochemical and genetic techniques show that it includes several quite different kinds of cells. They are found only in moist or aquatic habitats. Many protozoan species are symbionts, some are parasites, and some are predators of soil bacteria and algae. About 30,000 protozoan species are known. The study of protists is called "protistology".[source?]



  1. "Giardiasis (beaver fever) Fact Sheet".
  2. Gunter, Michelle 2008. Passing the North Carolina 8th grade end of grade test of science. American Book Company. ISBN 978-1-59807-186-3