Small, usually single-celled microorganism that lives in the soil They are non-photosynthetic and feed upon dead or live bacteria and fragments of organic matter
Are microscopic animals that occur as single cells Some protozoa can cause disease in humans Protozoa form cysts, which are specialized cells like eggs that are very resistant to chlorine Cysts can survive the disinfection process, then "hatch" into normal cells that can cause disease Protozoa must be removed from drinking water by filtration, because they cannot be effectively killed by chlorine
A large group of one-celled (unicellular) animals, including amoebas Some protozoa cause parasitic opportunistic infections in people with AIDS, notably toxoplasmosis and cryptosporidiosis