<P> Eukaryota (represented by the Australian green tree frog, left), </P> <P> Bacteria (represented by Staphylococcus aureus, middle) and </P> <P> In biological taxonomy, a domain (Latin: regio), also superkingdom or empire, is the highest taxonomic rank of organisms in the three - domain system of taxonomy designed by Carl Woese, an American microbiologist and biophysicist . According to the Woese system, introduced in 1990, the tree of life consists of three domains: Archaea, Bacteria, and Eukarya . The first two are all prokaryotic microorganisms, or single - celled organisms whose cells have no nucleus . All life that has a nucleus and membrane - bound organelles, and multicellular organisms, is included in the Eukarya . Stefan Luketa in 2012 proposed a five "dominion" system, adding two more to the above . </P> <P> The term "domain" is proposed by Woese et al. (1990) in his three - domain system . This term represents a synonym for the category of dominion (lat . dominium), introduced by Moore in 1974 . However, only Stefan Luketa uses the term "dominion". He placed Prion and Virus under two "dominions" separately . </P>

Why are organisms placed into the domain of eukarya
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