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The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
The last universal common ancestor (LUCA) was an organism which had ribosomes and the genetic code; it lived some 4 billion years ago. It gave rise to two main branches of prokaryotic life, the bacteria and the archaea. From among these small-celled, rapidly-dividing ancestors arose the Eukaryotes, with much larger cells, nuclei, and ...
The eukaryotes (/ j uː ˈ k ær i oʊ t s,-ə t s / yoo-KARR-ee-ohts, -əts) [4] constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals , plants , fungi , seaweeds , and many unicellular organisms are eukaryotes.
According to the domain system, the tree of life consists of either three domains, Archaea, Bacteria, and Eukarya, [1] or two domains, Archaea and Bacteria, with Eukarya included in Archaea. [3] [4] In the three-domain model, the first two are prokaryotes, single-celled microorganisms without a membrane-bound nucleus.
Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. [16] This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. [ 13 ]
The other three kingdoms in his system were the eukaryotic Fungi, Animalia, and Plantae. Whittaker, however, did not believe that all his kingdoms were monophyletic. [25] Whittaker subdivided the kingdom into two branches containing several phyla: Myxomonera branch Cyanophyta, now called Cyanobacteria; Myxobacteria; Mastigomonera branch Eubacteriae
For the Prokaryotes (Bacteria and Archaea) the rank kingdom has not been used till 2024 [115] (although some authors referred to phyla as kingdoms [73]). The category of kingdom was included into the Bacteriological Code in November 2023, [ 116 ] the first four proposals ( Bacillati , Fusobacteriati , Pseudomonadati , Thermotogati ) were ...
[1] [2] [3] It emerged from development of knowledge of archaea diversity and challenges the widely accepted three-domain system that classifies life into Bacteria, Archaea, and Eukarya. [4] It was preceded by the eocyte hypothesis of James A. Lake in the 1980s, [5] which was largely superseded by the three-domain system, due to evidence at the ...