Protozoa
From Wikipedia, the free encyclopedia
Leishmania donovani, (a species of protozoa) in a bone marrow cell
Protozoa are a diverse group of single-cell eukaryotic organisms,[1] many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement. Protozoa were regarded as the partner group of protists to protophyta, which have plant-like behaviour
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A unicellular organism, also known as a single-celled organism is an organism that consists of only one cell, in contrast to a multicellular organism that consists of multiple cells. Historically simple single celled organisms have sometimes been referred to as monads [1]
Prokaryotes, most protists, and some kinds of fungi are unicellular. Although some of these organisms live in colonies, they are still unicellular. These organisms live together, and each cell in the colony is the same. However, each cell must carry out all life processes in order for that cell to survive. In contrast, even the simplest multicellular organisms have specialized cells that depend on each other in order to survive.
Most unicellular organisms are of microscopic size and are thus classified as microorganisms. However, some unicellular protists and bacteria are macroscopic and visible to the naked eye.[2] Examples include:
Xenophyophores are the largest examples known, at roughly 4 inches.[3]
Valonia ventricosa.
Valonia ventricosa, with a diameter of 1 to 4 centimeters it is one of the largest single-celled organisms.[4][5]
Syringammina fragilissima
Thiomargarita namibiensis