Definition
Etymologically, microorganisms are small organisms whose size is too small to be observed by the naked eye. The resolution of the human eye is 0.2 mm, and this establishes 1 mm as an artificial limit for the maximum size of microorganisms. Taxonomically, “microorganism” lacks a precise meaning, and the term includes prokaryots (bacteria and archaea) and eukaryots (protists, microscopic algae, and fungi), which are all unicellular or lacking true tissues. Exceptionally, virus should be included in the definition of “microorganisms,” even though they lack cellular arrangement. Microbiology is the area of biological sciences that studies microorganisms. Prokaryots are the main focus of study in Microbiology. All are unicellular and lack a nucleus (pro-karion); their response to oxygen is very diverse; they can be auto- or heterotrophic and they employ the entire range of energy-obtaining systems found in living beings: anaerobic or aerobic respiration, fermentation...
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2011 Springer-Verlag Berlin Heidelberg
About this entry
Cite this entry
Sanz, J.L. (2011). Microorganism. In: Gargaud, M., et al. Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-11274-4_992
Download citation
DOI: https://doi.org/10.1007/978-3-642-11274-4_992
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-642-11271-3
Online ISBN: 978-3-642-11274-4
eBook Packages: Physics and AstronomyReference Module Physical and Materials ScienceReference Module Chemistry, Materials and Physics