Taxobox | color = khaki
name = Protist
image_width = 250px
domain_authority=Whittaker & Margulis, 1978
regnum = Protista*
regnum_authority = Haeckel,
subdivision_ranks = Typical phyla
** Cryptophyta (cryptomonads)
*** Ciliophora (ciliates)
** Rhodophyta (red algae)
Protists (IPAEng|ˈproʊtɨst), are a diverse group of eukaryotic
microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy.citation | author = Simonite, T. | year = 2005 | title = Protists push animals aside in rule revamp | journal = Nature | volume = 438 | issue = 7064 | pages = 8–9 | doi = 10.1038/438008b | url = http://www.ncbi.nlm.nih.gov/pubmed/16267517] The protists do not have much in common besides a relatively simple organization -- either they are unicellular, or they are multicellularwithout specialized tissues. This simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants.
The term "protista" was first used by
Ernst Haeckelin 1866. Protists were traditionally subdivided into several groups based on similarities to the "higher" kingdoms: the one-celledanimal-like protozoa, the plant-like protophyta(mostly one-celled algae), and the fungus-like slime molds and water molds. Because these groups often overlap, they have been replaced by phylogenetic-based classifications. However, they are still useful as informal names for describing the morphology and ecologyof protists.
Protists live in almost any environment that contains liquid water. Many protists, such as the
algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton. Other protists, such as the Kinetoplastids and Apicomplexaare responsible for a range of serious human diseases, such as malariaand sleeping sickness.
The first division of the protists from other organisms came in the 1820's, when the German biologist Georg A. Goldfuss introduced the word "
protozoa" to refer to organisms such as ciliates and corals.cite journal | author = Scamardella, J. M. |title = Not plants or animals: a brief history of the origin of Kingdoms Protozoa, Protista and Protoctista | year = 1999 | journal = International Microbiology | volume = 2 | pages = 207–221 | url = http://www.im.microbios.org/08december99/03%20Scamardella.pdf] This group was expanded in 1845 to include all "unicellular animals", such as Foraminiferaand amoebae. The formal taxonomic category "Protoctista" was first proposed in the early 1860's John Hogg, who argued that the protists should include what he saw as primitive unicellular forms of both plants and animals. He defined the Protoctista as a "fourth kingdom of nature", in addition to the then-traditional kingdoms of plants, animals and minerals. The kingdom of minerals was later removed from taxonomy by Ernst Haeckel, leaving plants, animals, and the protists as a “kingdom of primitive forms”.cite journal | author = Rothschild, L. J. | year = 1989 | title = Protozoa, protista, protoctista: What's in a name? | journal = Journal of the History of Biology | volume = 22 | issue = 2 | pages = 277–305 | doi = 10.1007/BF00139515 | url = http://www.springerlink.com/index/LW54T61737212643.pdf]
Herbert Copeland resurrected Hogg's label almost a century later, arguing that "Protoctista" literally meant "first established beings", Copeland complained that Haeckel's term "protista" included anucleated microbes such as
bacteria. Copeland's use of the term "protoctista" did not. In contrast, Copeland's term included nucleated eukaryotes such as diatoms, green algaeand fungi.cite journal | author = Copeland, H. F. | year = 1938 | title = The Kingdoms of Organisms | journal = Quarterly Review of Biology | volume = 13 | issue = 4 | pages = 383 | doi = 10.1086/394568 | url = http://links.jstor.org/sici?sici=0033-5770(193812)13%3A4%3C383%3ATKOO%3E2.0.CO%3B2-K] This classification was the basis for Whittaker's later definition of Fungi, Animalia, Plantaeand Protista as the four kingdoms of life.cite journal | author = Whittaker, R. H. | year = 1959 | title = On the Broad Classification of Organisms | journal = Quarterly Review of Biology | volume = 34 | issue = 3 | pages = 210 | doi = 10.1086/402733 | url = http://links.jstor.org/sici?sici=0033-5770(195909)34%3A3%3C210%3AOTBCOO%3E2.0.CO%3B2-J] The kingdom Protista was later modified to separate prokaryotes into the separate kingdom of Monera, leaving the protists as a group of eukaryotic microorganisms. [cite journal |author=Whittaker RH |title=New concepts of kingdoms or organisms. Evolutionary relations are better represented by new classifications than by the traditional two kingdoms |journal=Science (journal) |volume=163 |issue=863 |pages=150–60 |year=1969 |month=January |pmid=5762760] These five kingdoms remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that neither protists or monera were single groups of related organisms (they were not monophyletic groups).
Currently, the term "protist" is used to refer to unicellular eukaryotes that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues.cite journal |author=Adl SM, Simpson AG, Farmer MA, "et al" |title=The new higher level classification of eukaryotes with emphasis on the taxonomy of protists |journal=J. Eukaryot. Microbiol. |volume=52 |issue=5 |pages=399–451 |year=2005 |pmid=16248873 |doi=10.1111/j.1550-7408.2005.00053.x] The term "protozoa" is used to refer to
heterotrophic species of protists that do not form filaments. These terms are not used in current taxonomy, and are retained only as convenient ways to refer to these organisms.
The taxonomy of protists is still changing. Newer classifications attempt to present monophyletic groups based on
ultrastructure, biochemistry, and genetics. Because the protists as a whole are paraphyletic, such systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes. The recent scheme by Adl "et al." (2005) is an example that does not bother with formal ranks (phylum, class, etc.) and instead lists organisms in hierarchical lists. This is intended to make the classification more stable in the long term and easier to update.
Some of the main groups of protists, which may be treated as phyla, are listed in the taxobox at right.cite journal|last=Cavalier-Smith|first=T.|authorlink=Thomas Cavalier-Smith|coauthors=Chao, E. E. Y.|year=2003|title= Phylogeny and classification of phylum Cercozoa (Protozoa) |journal=Protist |volume=154 |issue=3–4 |pages=341–358 |doi=10.1078/143446103322454112] Many are thought to be monophyletic, though there is still uncertainty. For instance, the
excavates are probably not monophyletic and the chromalveolates are probably only monophyletic if the haptophytes and cryptomonads are excluded. [cite journal | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1713255 | title = Evaluating Support for the Current Classification of Eukaryotic Diversity | author = Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz | doi = 10.1371/journal.pgen.0020220 | journal = PLoS Genet. | date = 2006 December | volume = 2 | issue = 12 | pages = e220 | pmid = 17194223]
Types of protists
Protozoa, the animal-like protists
Protozoa are mostly single-celled,
motileprotists that feed by phagocytosis, though there are numerous exceptions. They are usually only 0.01–0.5 mm in size, generally too small to be seen without magnification. Protozoa are grouped by method of locomotioninto:
Some species, for example "
Plasmodium falciparum", have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually. [cite journal |author=Talman AM, Domarle O, McKenzie FE, Ariey F, Robert V |title=Gametocytogenesis: the puberty of Plasmodium falciparum |journal=Malar. J. |volume=3 |issue= |pages=24 |year=2004 |month=July |pmid=15253774 |pmc=497046 |doi=10.1186/1475-2875-3-24 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15253774] However, it is unclear how frequently sexual reproduction causes genetic exchange between different strains of "Plasmodium" in nature and most populations of parasitic protists may be clonal lines that rarely exchange genes with other members of their species. [cite journal |author=Tibayrenc M, Kjellberg F, Arnaud J, "et al" |title=Are eukaryotic microorganisms clonal or sexual? A population genetics vantage |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=88 |issue=12 |pages=5129–33 |year=1991 |month=June |pmid=1675793 |pmc=51825 |url=http://www.pnas.org/cgi/pmidlookup?view=long&pmid=1675793]
Marguilis, L., Corliss, J.O., Melkonian, M.,and Chapman, D.J. (Editors) 1990. "Handbook of Protoctista." Jones and Bartlett , Boston. ISBN 0-86720-052-9
* [http://tolweb.org/Eukaryotes/3 Tree of Life: Eukaryotes]
* [http://phylogenetics.bioapps.biozentrum.uni-wuerzburg.de/etv/ A java applet for exploring the new higher level classification of eukaryotes]
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Look at other dictionaries:
protist — PROTÍST, protiste, s.n. Microorganism unicelular. – Din fr. protiste. Trimis de ana zecheru, 19.04.2004. Sursa: DEX 98 PROTÍST s. v. protozoar. Trimis de siveco, 13.09.2007. Sursa: Sinonime protíst s. n., pl. protíste … Dicționar Român
Protist — Pro tist, n. (Zo[ o]l.) One of the Protista. [1913 Webster] … The Collaborative International Dictionary of English
protist — 1869, from Mod.L. protista, from Gk. neut. pl. of protistos вЂњthe very first,вЂќ superlative of protos вЂњfirstвЂќ (see PROTO (Cf. proto )) … Etymology dictionary
protist — [prōt′ist] n. [< Gr prōtistos, first < prōtos, first: see PROTO ] Biol. in some systems of classification, any of a kingdom (Protista) of one celled organisms, as algae, yeasts, or protozoans, having characteristics found in both plants and … English World dictionary
protist — protistan /proh tis teuhn/, adj., n. protistic, adj. /proh tist/, n. any of various one celled organisms, classified in the kingdom Protista, that are either free living or aggregated into simple colonies and that have diverse reproductive and… … Universalium
Protist — protistai statusas T sritis ekologija ir aplinkotyra apibrėžtis Grupė vienaląsčių organizmų, turinčių branduolį ir sudėtingos sandaros (eukariotines) ląsteles. atitikmenys: angl. protist vok. Protist, m rus. протисты … Ekologijos terminų aiškinamasis žodynas
protist — protistai statusas T sritis ekologija ir aplinkotyra apibrėžtis Grupė vienaląsčių organizmų, turinčių branduolį ir sudėtingos sandaros (eukariotines) ląsteles. atitikmenys: angl. protist vok. Protist, m rus. протисты … Ekologijos terminų aiškinamasis žodynas
protist — noun Etymology: New Latin Protista, from Greek, neuter plural of prōtistos very first, primal, from superlative of prōtos first more at prot Date: 1889 any of a diverse taxonomic group and especially a kingdom (Protista syn. Protoctista) of… … New Collegiate Dictionary
Protist — Die Protisten (Protista) sind eukaryotische, ein bis wenigzellige Lebewesen, die aber nicht näher miteinander verwandt sind. Früher wurden sie als eigenes Reich innerhalb der Eukaryoten zusammengefasst und den Pflanzen (Reich Plantae), Tieren… … Deutsch Wikipedia
protist — noun Any of the eukaryotic unicellular organisms including protozoans, slime molds and some algae; historically grouped into the kingdom Protoctista. See Also: protistologist, protistology, protistological … Wiktionary