Archaea

Archaea is one of the three domains of life (the other two being prokaryotes and eukarya). It comprises single-celled organisms, similar in size and shape to prokaryotes, that, like prokaryotes, lack internally compartmentalized organelles. It was established as a separate domain from prokaryotes after biochemical and genetic studies revealed that archaeans formed a genetically distinct group, with distinctive biochemistry (notably in the lipid composition of their cell membranes) and metabolic pathways.