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The hierarchy of biological classification's major eight taxonomic ranks. Taxonomic rank ( rank, category, taxonomic category is an abstract term used in the Scientific classification, or Taxonomy, of organisms A domain contains one or more kingdoms. In biological Taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest Taxonomic rank of Organisms Intermediate minor rankings are not shown.

From biological taxonomy, a kingdom or regnum is a taxonomic rank in either (historically) the highest rank, or (in the new three-domain system) the rank below domain. Foundations of modern biology There are five unifying principles Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos Taxonomic rank ( rank, category, taxonomic category is an abstract term used in the Scientific classification, or Taxonomy, of organisms The three-domain system is a Biological classification introduced by Carl Woese in 1990 that divides cellular life forms into Archaea, Taxonomic rank ( rank, category, taxonomic category is an abstract term used in the Scientific classification, or Taxonomy, of organisms In biological Taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest Taxonomic rank of Organisms Each kingdom is divided into smaller groups called phyla (or in some contexts these are called "divisions"). A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. Currently, textbooks from the United States use a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea, and Eubacteria), while British and Australian textbooks describe five kingdoms (Animalia, Plantae, Fungi, Protista, and Prokaryota or Monera). Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell

Carolus Linnaeus distinguished two kingdoms of living things: Animalia for animals and Vegetabilia for plants (Linnaeus also treated minerals, placing them in a third kingdom, Mineralia). Carl Linnaeus (Latinized as Carolus Linnaeus, also known after his ennoblement as, May 23 new style (13 May old style 1707 who laid the foundations for Plants are living Organisms belonging to the kingdom Plantae. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Linnaeus divided each kingdom into classes, later grouped into phyla for animals and divisions for plants. A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class.

It gradually became apparent how important the prokaryote/eukaryote distinction is, and Stanier and van Niel popularized Edouard Chatton's proposal in the 1960s. Edouard Chatton (1883 — 1947 was a French biologist who first distinguished between the Eukaryotic and Prokaryotic systems of cellular organisation and coined ^[1]

Five kingdoms

R. H. Whittaker recognized an additional kingdom for the Fungi. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ The resulting five-kingdom system, proposed in 1968, has become a popular standard and with some refinement is still used in many works, or forms the basis for newer multi-kingdom systems. It is based mainly on differences in nutrition; his Plantae were mostly multicellular autotrophs, his Animalia multicellular heterotrophs, and his Fungi multicellular saprotrophs. Nutrition (also called nourishment or aliment) is the provision to cells and Organisms of the materials necessary (in the form of food to support An autotroph (from the Greek autos = self and trophe = nutrition is an Organism that produces complex Organic compounds from simple A heterotrophs, or chemoorganotrophy ( Greek heterone = (another and trophe = nutrition is an Organism that requires The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies. ^[2]

Six kingdoms

In the years around 1980 there was an emphasis on phylogeny and redefining the kingdoms to be monophyletic groups, groups made up of relatively closely related organisms. The Animalia, Plantae, and Fungi were generally reduced to core groups of closely related forms, and the others placed into the Protista. Based on RNA studies Carl Woese divided the prokaryotes (Kingdom Monera) into two kingdoms, called Eubacteria and Archaebacteria. Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Carl Richard Woese (born July 15 1928, Syracuse New York) is an American Microbiologist who attended Deerfield Academy The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Carl Woese attempted to establish a Three Primary Kingdom (or Urkingdom) system in which Plants, Animals, Protista, and Fungi were lumped into one primary kingdom of all eukaryotes. The Eubacteria and Archaebacteria made up the other two urkingdoms. The initial use of "six Kingdom systems" represents a blending of the classic Five Kingdom system and Woese's Three Kingdom system. Such six Kingdom systems have become standard in many works. ^[3]

A variety of new eukaryotic kingdoms were also proposed, but most were quickly invalidated, ranked down to phyla or classes, or abandoned. The only one which is still in common use is the kingdom Chromista proposed by Cavalier-Smith, including organisms such as kelp, diatoms, and water moulds. The Chromista are a eukaryotic supergroup probably Polyphyletic, Professor Thomas (Tom Cavalier-Smith (born October 21 1942) FRS, FRSC, NERC Professorial Fellow is a Professor of Kelp are large Seaweeds ( Algae) belonging to the Brown algae and classified in the order Laminariales Diatoms ( Greek: (dia = "through" + (temnein = "to cut" i Oomycetes also known as Water molds (or water moulds: see spelling differences) are a group of filamentous unicellular Heterokonts physically Thus the eukaryotes are divided into three primarily heterotrophic groups, the Animalia, Fungi, and Protozoa, and two primarily photosynthetic groups, the Plantae (including red and green algae) and Chromista. The red algae (Rhodophyta ˌroʊdəˈfaɪtə roʊˈdɒfɨtə from Greek: ῥόδον (rhodon = rose + φυτόν (phyton = plant thus red plant are The green algae (singular green alga) are the large group of Algae from which the Embryophytes (higher plants emerged However, it has not become widely used because of uncertainty over the monophyly of the latter two kingdoms.

Woese stresses genetic similarity over outward appearances and behaviour, relying on comparisons of ribosomal RNA genes at the molecular level to sort out classification categories. A plant does not look like an animal, but at the cellular level, both groups are eukaryotes, having similar subcellular organization, including cell nuclei, which the Eubacteria and Archaebacteria do not have. More importantly, plants, animals, fungi, and protists are more similar to each other in their genetic makeup at the molecular level, based on rRNA studies, than they are to either the Eubacteria or Archaebacteria. Woese also found that all of the eukaryotes, lumped together as one group, are more closely related, genetically, to the Archaebacteria than they are to the Eubacteria. This means that the Eubacteria and Archaebacteria are separate groups even when compared to the eukaryotes. So, Woese established the Three-domain system, clarifying that all the Eukaryotes are more closely genetically related compared to their genetic relationship to either the bacteria or the archaebacteria, without having to replace the "six kingdom systems" with a three kingdom system. The three-domain system is a Biological classification introduced by Carl Woese in 1990 that divides cellular life forms into Archaea, The Three Domain system is a "six kingdom system" that unites the eukaryotic kingdoms into the Eukarya Domain based on their relative genetic similarity when compared to the Bacteria Domain and the Archaea Domain. Woese also recognized that the Protista Kingdom is not a monophyletic group and might be further divided at the level of Kingdom. Others have divided the Protista Kingdom into the Protozoa and the Chromista, for instance.

Recent Advances

Classification is an ongoing area of research and discussion. As new findings and technologies become available they allow the refinement of the model. For example, gene sequencing techniques allow the comparison of the genome of different groups (Phylogenomics). Phylogenomics can be regarded as the intersection between the fields of evolution and genomics. A study published in 2007 by Fabien Burki, et al^[4] proposes four high level groups of eukaryotes based on phylogenomics research.

1. Plantae (green and red algae, and plants)
2. Opisthokonts (amoebas, fungi, and animals)
3. Excavata (free-living and parasitic protists)
4. SAR (acronym for Stramenopiles, Alveolates, and Rhizaria–the names of some of its members. Plants are living Organisms belonging to the kingdom Plantae. The opisthokonts ( Greek: (opisthō- = "rear posterior" + (kontos = "pole" i The excavates are a major assemblage of Protists often known as Excavata. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The heterokonts or stramenopiles are a major line of Eukaryotes presently containing about 10500 known species The alveolates ("with cavities" are a major line of Protists There are three phyla, which are very divergent in form but are now known to be close relatives The Rhizaria are a species-rich supergroup of Protists They vary considerably in form but for the most part they are Amoeboids with filose reticulose or microtubule-supported Burki found that the previously split groups Rhizaria and Chromalveolates were more similar in 123 common genes than once thought. Chromalveolata is a Eukaryote supergroup first proposed by Thomas Cavalier-Smith as a refinement of his kingdom Chromista, which was first )

Summary

(Note that the equivalences in this table are not perfect. The three-domain system is a Biological classification introduced by Carl Woese in 1990 that divides cellular life forms into Archaea, Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Plants are living Organisms belonging to the kingdom Plantae. Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Plants are living Organisms belonging to the kingdom Plantae. Plants are living Organisms belonging to the kingdom Plantae. Plants are living Organisms belonging to the kingdom Plantae. e. g. Haeckell placed the red algae (Haeckell's Florideae; modern Florideophyceae) and blue-green algae (Haeckell's Archephyta; modern Cyanobacteria) in his Plantae, but in modern classifications the empires are erroneously attributed to Chatton in the table who did not rank the 2 groups nor formally name them). The red algae (Rhodophyta ˌroʊdəˈfaɪtə roʊˈdɒfɨtə from Greek: ῥόδον (rhodon = rose + φυτόν (phyton = plant thus red plant are Florideophyceae is a class of Red algae They were once thought to be the only algae to bear Pit connections but these have since been found in the filamentous Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy

In 1998 Cavalier-Smith divided Protista in 2 new kingdoms: Chromista the phylogenetic group of golden-brown algae that includes those algae whose chloroplasts contain chlorophylls a and c, as well as various colorless forms that are closely related to them, and Protozoa, the kingdom of protozoans. Professor Thomas (Tom Cavalier-Smith (born October 21 1942) FRS, FRSC, NERC Professorial Fellow is a Professor of The Chromista are a eukaryotic supergroup probably Polyphyletic, Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular

• Cavalier-Smith, T. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Plants are living Organisms belonging to the kingdom Plantae. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ The Chromista are a eukaryotic supergroup probably Polyphyletic, Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular 2006. Protozoa: the most abundant predators on earth, Microbiology Today, Nov. 2006, pp. 166-167. (pdf aquí).

References

See also

• Cladistics
• Systematics

External links

• The five kingdom concept
• Whittaker's classification