The Three Domain System
Thissystemofclassificationwasintroduced by C.Woese, O. Kandler and M.L.Wheelis, is an evolutionary model of phylogeny based on cells rRNA sequences(differences in the sequences of nucleotides) studies. They grouped all living organisms into three domains: Bacteria, Archaea and Eukaryota (Figure 8.5).
Bacteria and Archaea are two different groups of prokaryotes. The domain Bacteria comprise the vast majority of prokaryotes. The domain Archaea contains prokaryotes that live mostly in extreme environments. The domain Eukaryota contains living organisms that includes Kingdom Protista, Kingdom Fungi, Kingdom Plantae and Kingdom
Animalia. This system of classification is currently accepted by most biologist.
The three domain system is based on the current state of knowledge. As knowledge of organisms increase in the future, classification will undoubtedly continue to change.
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