Unicellular organism

Unicellular organisms are organisms that consist of only one cell. They are compared to the multi-celled or multicellular. The division into single and multi- Zeller is purely descriptive and gives no information on degree of relationship, lifestyle or internal structure and metabolic processes. Unicellular therefore not form a closed kinship group. Single-celled animals include all archaea, most Bacteria, some fungi and protists many. They vary in size from less than a 1 micron (eg Nanoarchaeum equitans ) and several centimeters (eg Acetabularia ). Some single-celled organisms can form cell colonies.

The first single-celled organisms were discovered in 1674 by Antoni van Leeuwenhoek. According to older views all eukaryotes were divided only into the two kingdoms of plants and animals, after which there was accordingly unicellular plants and animals. For example, the amoebae were counted as single-celled animals, some of their representatives to the slime molds and flagellate flagellate Euglena as alternately to the unicellular algae or unicellular animals.