AskDefine | Define protozoa

Dictionary Definition

Protozoa n : in some classifications considered a superphylum or a subkingdom; comprises flagellates; ciliates; sporozoans; amoebas; foraminifers [syn: phylum Protozoa]protozoan adj : of or relating to the Protozoa [syn: protozoal, protozoic] n : any of diverse minute acellular or unicellular organisms usually nonphotosynthetic [syn: protozoon] [also: protozoa (pl)]protozoa See protozoan

User Contributed Dictionary

see Protozoa



protozoa p
  1. Plural of protozoan
  2. Plural of protozoon

Extensive Definition

Protozoa (in Greek protohi = first and zoa = animals) 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. The name 'protozoa' is used for the more animal-like single celled organisms like amoebas and ciliates. The term 'algae' is used for the more plant-like micro organisms. However, the distinction between the two is often vague. Dinobryon (top image) has chloroplasts for photosynthesis but it can also feed on organic matter. It is even able to swim. Such an organism can neither be animal nor plant. Nowadays, all these unicellular organisms that are neither animals, plants, bacteria or fungi are called 'protists‘.


Protozoa are around 10–50 μm, but can grow up to 1 mm and can easily be seen under a microscope. Protozoa exist throughout aqueous environments and soil. Protozoa occupy a range of trophic levels. As predators, they prey upon unicellular or filamentous algae, bacteria, and microfungi. Protozoa play a role both as herbivores and as consumers in the decomposer link of the food chain. Protozoa also play a vital role in controlling bacteria populations and biomass. As components of the micro- and meiofauna, protozoa are an important food source for microinvertebrates. Thus, the ecological role of protozoa in the transfer of bacterial and algal production to successive trophic levels is important. Protozoa such as the malaria parasites (Plasmodium spp.), trypanosomes and leishmania are also important as parasites and symbionts of multicellular animals.
Most protozoa exist in 5 stages of life which are in the form of trophozoites and 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, and some both (eg. Coccidia). An individual protozoan is hermaphroditic.
Another name for protozoa is Acrita (R. Owen, 1861). It can also be considered ''Eukaryotic Cell Functionase


Protozoa were commonly grouped in the kingdom of Protista together with the plant-like algae and fungus-like water molds and slime molds. In the 21st-century systematics, protozoans, along with ciliates, mastigophorans, and apicomplexans, are arranged as animal-like protists. However, protozoans are neither Animalia nor Metazoa (with the possible exception of the enigmatic, moldy Myxozoa).


Protozoa have traditionally been divided on the basis of their means of locomotion, although this is no longer believed to represent genuine relationships:

External links

protozoa in Arabic: أوليات
protozoa in Catalan: Protozou
protozoa in Czech: Prvoci
protozoa in Danish: Protozo
protozoa in German: Protozoen
protozoa in Modern Greek (1453-): Πρωτόζωο
protozoa in Esperanto: Protozooj
protozoa in Spanish: Protozoo
protozoa in Persian: تک‌یاختگان
protozoa in Finnish: Alkueläimet
protozoa in Indonesian: Protozoa
protozoa in Italian: Protozoa
protozoa in Japanese: 原生動物
protozoa in Latin: Protozoa
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protozoa in Macedonian: Праживотни
protozoa in Malay (macrolanguage): Protozoa
protozoa in Dutch: Protozoa
protozoa in Polish: Protisty zwierzęce
protozoa in Portuguese: Protozoário
protozoa in Romanian: Protozoar
protozoa in Simple English: Protozoa
protozoa in Slovenian: Praživali
protozoa in Serbian: Протозоа
protozoa in Swedish: Urdjur
protozoa in Thai: โพรโทซัว
protozoa in Vietnamese: Động vật nguyên sinh
protozoa in Walloon: Protozowaire
protozoa in Chinese: 原生动物门
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