Archaea

Structure
Archea are very similar to bacteria (in size, shape, absence of membrane bound organelles). Until 1990, they were considered an unusual group of bacteria and named archaebacteria. They were given their own domain since they have gone through an independent evolution and have many differences in their biochemistry from other forms of life. Archaea reproduce asexually and divide by binary fission, fragmentation, or budding; in contrast to bacteria archaea do not form spores. Initially, archaea were seen as extremophiles that lived in harsh environments, such as hot springs and salt lakes, but they have since been isolated from various habitats including soils, oceans, and marshlands. One example are the methanogenic archaea that inhabit the gut of humans and ruminants, where they are present in vast numbers and aid in the digestion of food.

Function
Archaea are important in technology; methanogens are used to produce biogas and as part of sewage treatment, and enzymes from extremophile archaea that can resist high temperatures and organic solvents are exploited in biotechnology.

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 * Prokaryotic Chromosomes
 * Structure and Function of Prokaryotes