    a microorganism (from the , mikros, "small" and , organismÃ³s, "organism") is a microscopic living organism, which may be a single cell or a multicellular organism. the study of microorganisms is called microbiology, a subject that began with the discovery of microorganisms in 1674 by antonie van leeuwenhoek, using a microscope of his own design. microorganisms are very diverse and include all the bacteria and archaea and almost all the protozoa. they also include some fungi, algae, and certain animals, such as rotifers. many macro animals and plants have juvenile stages which are also microorganisms. some microbiologists also classify viruses (and viroids) as microorganisms, but others consider these as nonliving. microorganisms live in every part of the biosphere, including soil, hot springs, "seven miles deep" in the ocean, "40 miles high" in the atmosphere and inside rocks far down within the earth's crust (see also endolith). microorganisms, under certain test conditions, have been observed to thrive in the vacuum of outer space.{{cite journal | title = biological responses to space: results of the experiment "exobiological unit" of era on eureca i | journal = adv space res. | year = 1995 | first1 = horneck g |las
Microorganisms