Singlecelled
Single-celled organisms are organisms composed of a single cell that carries out all essential life processes. They can be prokaryotic, lacking a defined nucleus, or eukaryotic, containing a nucleus and organelles. The category includes bacteria, archaea, many protists, and some fungi such as yeasts.
Most are microscopic, typically measuring a few micrometers in size, and exhibit a range of shapes from
Single-celled organisms occupy nearly every habitat, including soil, freshwater, oceans, and extreme environments such as hot
Ecologically and scientifically, unicellular life is foundational. Unicellular organisms were among the first life forms on
Examples include bacteria such as Escherichia coli and Bacillus subtilis; archaea such as Halobacterium; unicellular fungi