Protozoa
Say it: proh-tuh-ZOH-uh
Protozoa are single-celled eukaryotes that do not photosynthesize, usually move on their own and feed on other organisms or organic matter.
Also: protozoan, protozoans, protozoon
Definition
What are protozoa?
Protozoa are single-celled eukaryotic organisms that take in food rather than making it and that can usually move. They are part of the protists, an informal collection of mostly microscopic eukaryotes that are not plants, animals or fungi. Protozoa arose in several separate branches of the tree of life, so the name describes a way of life rather than one natural group.
Protozoa move with whip-like flagella, with hair-like cilia or with pseudopodia, the flowing extensions of cytoplasm used by amoebas. Many feed by engulfing food particles. The active, feeding form is called a trophozoite, and many species can also form a cyst, a dormant stage with a tough wall that survives outside a host. They reproduce mainly by binary fission, and some also by multiple fission or by sexual processes. An older scheme based on movement sorts them into amoebas, flagellates, ciliates and sporozoans, whose adult stage cannot move.
Most protozoa live freely in water and soil, but some cause major diseases: Plasmodium causes malaria, Giardia and Entamoeba cause diarrheal illness, and Trypanosoma causes sleeping sickness and Chagas disease. Intestinal species usually spread through contaminated food or water, and those in the blood through insect bites.
Word parts
Where does the word “protozoa” come from?
- proto-
- firstGreek prōtos
- -zoa
- animalsGreek zōion
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Terms that go with it
- ParasiteA parasite is a living thing that makes its home on or inside a host organism and feeds from it, usually causing the host harm.
- PlasmodiumPlasmodium is a genus of single-celled parasites, spread by Anopheles mosquitoes, that infect liver and red blood cells and cause malaria.
- EukaryoteA eukaryote is an organism whose cells keep their DNA inside a membrane-bound nucleus and contain other membrane-bound organelles.
- VectorIn disease biology, a vector is a living organism, often a bloodsucking insect or tick, that carries a pathogen from one host to another.
- Binary fissionBinary fission is how bacteria and archaea reproduce: a cell copies its DNA, grows, and splits in the middle into two identical daughter cells.
- PathogenA pathogen is a microbe or other agent, such as a virus, bacterium, fungus, parasite or prion, that can cause disease in a host.
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