Protozoa facts for kids
Protozoa are small (but not simple) organisms. They are single-celled heterotrophic eukaryotes, which eat bacteria and other food sources.
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. 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.
Related pages
Images for kids
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Class Protozoa, order Infusoria, family Monades by Georg August Goldfuss, c. 1844
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John Hogg's illustration of the Four Kingdoms of Nature, showing "Primigenal" as a greenish haze at the base of the Animals and Plants, 1860
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The ciliate Spirostomum ambiguum can attain 3 mm in length
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Isotricha intestinalis, a ciliate present in the rumen of sheep.
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Paramecium bursaria, a ciliate which derives some of its nutrients from algal endosymbionts in the genus Chlorella
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Trophozoites of the amoebic dysentery pathogen Entamoeba histolytica with ingested human red blood cells (dark circles)
