Microorganism

From Freepedia

A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). Microorganisms are often illustrated using single-celled, or unicellular organisms; however, some unicellular protists are visible to the naked eye, and some multicellular species are microscopic. The study of microorganisms is called microbiology.

Microorganisms and unicellular organisms

Microorganisms may be found almost anywhere in the taxonomic structure. Bacteria and archaea are almost always microscopic. A number of eukaryotes are also microscopic, including most protists and a number of fungi.

Unicellular species are those whose members consist of a single cell throughout their life cycle. This latter qualification is significant since all multicellular organisms consist of a single cell at the beginning of their life cycles. Usually, unicellular organisms contain only a single copy of their genome (except when undergoing cell division), although some organisms have multiple cell nuclei (see coenocyte).