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Bacteria Archaea Eucaryota Aquifex Thermotoga Cytophaga Bacteroides Bacteroides-Cytophaga Planctomyces Cyanobacteria Proteobacteria Spirochetes Gram-positive bacteria Green filantous bacteria Pyrodicticum Thermoproteus Thermococcus celer Methanococcus Methanobacterium Methanosarcina Halophiles Entamoebae Slime mold Animal Fungus Plant Ciliate Flagellate Trichomonad Microsporidia Diplomonad
A phylogenetic tree based on rRNA data, showing the separation of bacteria, archaea, and eukaryotes.

The three-domain system is a biological classification introduced by Carl Woese in 1990[1] that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea). Woese argued that, on the basis of differences in 16S rRNA genes, these two groups and the eukaryotes each arose separately from an ancestor with poorly developed genetic machinery, often called a progenote. To reflect these primary lines of descent, he treated each as a domain, divided into several different kingdoms.

Contents

Classification

The three-domain system is loosely based on the traditional five-kingdom system but divides the Monera into two "domains," leaving the remaining eukaryotic kingdoms in the third domain. The current system has the following kingdoms in the three domains:

Archaea Domain - prokaryotic, no nuclear membrane, distinct biochemistry and RNA markers from eubacteria, possess unique ancient evolutionary history for which they are considered some of the oldest species of organisms on Earth; traditionally classified as archaebacteria; often characterized by living in extreme environments

  • Methanogens - metabolize hydrogen and carbon dioxide into methane
  • Halophiles - thrive in salt
  • Thermoacidophiles - thrive in acid and high temperatures (up to 110 degrees Celsius)


Bacteria Domain - prokaryotic, no nuclear membrane, traditionally classified as bacteria, contain all known pathogenic prokaryotic organisms, studied far more extensively than Archaea

  • Cyanobacteria - photosynthesizing bacteria
  • Spirochaete - Gram-negative bacteria that include those causing syphilis and Lyme disease
  • Firmicutes - Gram-positive bacteria including Bifidobacterium animalis which is present in the human large intestine


Eukarya Domain - eukaryotes, nuclear membrane

  • Rhodophyta - red algae
  • Chromalveolata - includes dinoflagellates
  • Saccharomycotina - includes true yeasts
  • Basidiomycota - includes shiitake mushrooms
  • Bryophyta - mosses
  • Magnoliophyta - flowering plants
  • Arthropoda - includes insects, arachnids, and crustaceans
  • Chordata - includes vertebrates and, as such, human beings

Niches

Each of the three cell types tends to fit into recurring specialties or roles. Bacteria tend to be the most prolific reproducers, at least in moderate environments. Archaeans tend to adapt quickly to extreme environments, such as high temperatures, high acids, high sulfur, etc. This includes adapting to use a wide variety of food sources. Eukaryotes are the most flexible with regard to forming cooperative colonies, such as in multi-cellular organisms, including humans. In fact, the structure of a Eukaryote is likely to have derived from a joining of different cell types, forming organelles.

See also

References

  1. ^ Woese C, Kandler O, Wheelis M (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya.". Proc Natl Acad Sci USA 87 (12): 4576–9. doi:10.1073/pnas.87.12.4576. PMID 2112744. http://www.pnas.org/cgi/reprint/87/12/4576. Retrieved 11 Feb 2010. 
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The three-domain system is a biological classification introduced by Carl Woese in 1990[1] that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea). Woese argued that, on the basis of differences in 16S rRNA genes, these two groups and the eukaryotes each arose separately from an ancestor with poorly developed genetic machinery, often called a progenote. To reflect these primary lines of descent, he treated each as a domain, divided into several different kingdoms.

Contents

Classification

The three-domain system is loosely based on the traditional five-kingdom system but divides the Monera into two "domains," leaving the remaining eukaryotic kingdoms in the third domain. The current system has the following kingdoms in the three domains:

Archaea Domain - prokaryotic, no nuclear membrane, distinct biochemistry and RNA markers from eubacteria, possess unique ancient evolutionary history for which they are considered some of the oldest species of organisms on Earth; traditionally classified as archaebacteria; often characterized by living in extreme environments

  • Methanogens - metabolize hydrogen and carbon dioxide into methane
  • Halophiles - thrive in salt
  • Thermoacidophiles - thrive in acid and high temperatures (up to 110 degrees Celsius)


Bacteria Domain - prokaryotic, no nuclear membrane, traditionally classified as bacteria, contain most known pathogenic prokaryotic organisms (see [2] for exceptions), studied far more extensively than Archaea

  • Cyanobacteria - photosynthesizing bacteria
  • Spirochaete - Gram-negative bacteria that include those causing syphilis and Lyme disease
  • Firmicutes - Gram-positive bacteria including Bifidobacterium animalis which is present in the human large intestine


Eukarya Domain - eukaryotes, nuclear membrane

  • Rhodophyta - red algae
  • Chromalveolata - includes dinoflagellates
  • Saccharomycotina - includes true yeasts
  • Basidiomycota - includes shiitake mushrooms
  • Bryophyta - mosses
  • Magnoliophyta - flowering plants
  • Arthropoda - includes insects, arachnids, and crustaceans
  • Chordata - includes vertebrates and, as such, human beings

Niches

Each of the three cell types tends to fit into recurring specialties or roles. Bacteria tend to be the most prolific reproducers, at least in moderate environments. Archaeans tend to adapt quickly to extreme environments, such as high temperatures, high acids, high sulfur, etc. This includes adapting to use a wide variety of food sources. Eukaryotes are the most flexible with regard to forming cooperative colonies, such as in multi-cellular organisms, including humans. In fact, the structure of a Eukaryote is likely to have derived from a joining of different cell types, forming organelles.

See also

References

  1. ^ Woese C, Kandler O, Wheelis M (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya.". Proc Natl Acad Sci USA 87 (12): 4576–9. doi:10.1073/pnas.87.12.4576. PMID 2112744. PMC 54159. http://www.pnas.org/cgi/reprint/87/12/4576. Retrieved 11 Feb 2010. 
  2. ^ Paul B. Eckburg, Paul W. Lepp, and David A. Relman (2003) Archaea and Their Potential Role in Human Disease. Infection and Immunity, p. 591-596, Vol. 71, No. 2 DOI: 10.1128/IAI.71.2.591-596.2003


The three domains of life are the following:

  • bacteria
  • Archaea
  • Eukarya

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