According to wikipedia: Protozoa are unicellular eukaryotes, (singular protozoan). While there is no exact definition of the term, most scientists use protozoan to refer to a unicellular heterotrophic protist, like amoebas and ciliates.Images of some medically important protozoa:
Some protozoa have life stages alternating between proliferative stages (eg trophozoites) and dormant cysts. As cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures and harmful chemicals, or long periods without access to nutrients, water, or oxygen for a period of time. Being a cyst enables parasitic species to survive outside of the host, and allows their transmission from one host to another.
When protozoa are in the form of trophozoites (Greek, tropho=to nourish), they actively feed and grow. The process by which the protozoa takes its cyst form is called encystation, while the process of transforming back into trophozoite is called excystation. Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while some use a combination, (eg. Coccidia). An individual protozoan is hermaphroditic.
Entamoeba hitolytica trophozoite
Entamoeba Histolytica cyst
Entamoeba Coli trophozoite
Entamoeba coli cyst
Balantidium Coli cyst
Giardia Lamblia trophozoite
Trichomona Vaginalis trophozoite
Naeglaria Fowleri in brain tissue
Acanthamoeba cyst in brain tissue
-Image credits: CDC.gov --- All images are in the public domain.
-For more free medical images: Medical Images Public Domain (a group on Flickr)
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