Microorganismsarethesmallest organisms on Earth. In fact,thetermmicroorganismliterallymeans"microscopic organism."Microorganismsmay be composed of prokaryotic or eukaryotic cells, and they may be single-celled or multicellular. Examples ofmicroorganismsinclude algae,fungi, protozoa,bacteriaand viruses.

Prokaryotic Microorganisms

Prokaryotes arguably represent the earliest forms of life on Earth. They are broken up into two categories: bacteria and archaea. A prokaryotic cell lacks a nucleus to hold the cell's DNA and lacks any sort of organized packaging or housing to hold the rest of the cell's machinery. Because prokaryotic cells lack this extra material, they are almost always smaller than other cell types; all prokaryotes are microorganisms, and they are almost always single-celled.

Eukaryotic Microorganisms

Eurkaryotic cells are larger and more complex than prokaryotic cells. The DNA of a eukaryotic cell is neatly packaged within its nucleus, and there are several different structures that house the cellular machinery that can make eukaryotic microorganisms self-sufficient. The structures located in eukaryotic cells may include the endoplasmic reticulum, golgi apparatus, mitochondria, and ribosomes, as well as chloroplasts in photosynthetic cells. Examples of eukaryotic microorganisms include fungi, algae, protozoa and various microscopic parasitic worms.