Unicellular

Unicellular organisms are organisms that consist of a single cell, unlike multicellular organisms that consist of many cells. The main groups of unicellular organisms are bacteria, archaea, protozoa, unicellular algae, and unicellular fungi. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms.

Characteristics

Unicellular organisms are usually microscopic, less than one tenth of a millimeter long. There are exceptions, such as the giant amoeba Chaos carolinense, which can reach lengths of 5 mm, and the even larger Valonia ventricosa, a species of alga which can reach 50 mm.

Classification

Unicellular organisms are divided into two types: prokaryotic and eukaryotic organisms. Prokaryotes include bacteria and archaea. Eukaryotes include protozoa, unicellular algae, and unicellular fungi.

Prokaryotic Unicellular Organisms

Prokaryotes are the most ancient form of life, with fossils dating back more than 3.5 billion years. They are characterized by the lack of a nucleus and other membrane-bound organelles.

Eukaryotic Unicellular Organisms

Eukaryotes have a nucleus and other membrane-bound organelles. They are more complex than prokaryotes and can perform more specialized functions.

Reproduction

Unicellular organisms reproduce through a process called binary fission, where the cell divides into two identical cells.

Evolution

The first life forms on Earth were likely unicellular organisms. Some of these evolved into multicellular organisms.

See also

• Cell (biology)
• Multicellular organism
• Colonial organism

References

Unicellular Resources
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