Protist 22932 225909404 2008-07-15T23:39:24Z Donald Albury 374244 /* Modern classifications */ typo {{Taxobox | color = khaki | name = Protist | fossil_range = [[Neoproterozoic]] - Recent | image = Protist collage.jpg | image_width = 250px | image_caption = | domain='''[[Eukarya]]''' | domain_authority=[[Robert Whittaker|Whittaker]] & [[Lynn Margulis|Margulis]], 1978 | regnum = '''Protista'''[[paraphyly|*]] | regnum_authority = [[Ernst Haeckel|Haeckel]], [[1866]] | subdivision_ranks = Typical phyla | subdivision = <div> *'''[[Chromalveolata]]''' ** [[Heterokont]]ophyta ** [[Haptophyte|Haptophyta]] ** [[Cryptomonad|Cryptophyta]] (cryptomonads) ** '''[[Alveolate|Alveolata]]''' *** [[Dinoflagellate|Dinoflagellata]] *** [[Apicomplexa]] *** [[Ciliate|Ciliophora]] (ciliates) *'''[[Cabozoa]]''' ** '''[[Excavate|Excavata]]''' *** [[Euglenozoa]] *** [[Percolozoa]] *** [[Metamonad]]a ** '''[[Rhizaria]]''' *** [[Radiolaria]] *** [[Foraminifera]] *** [[Cercozoa]] * '''[[Archaeplastida]] (in part)''' ** [[Red alga|Rhodophyta]] (red algae) ** [[Glaucophyta]] (basal archaeplastids) * '''[[Unikonta]] (in part)''' ** [[Amoebozoa]] ** [[Choanozoa]] <center><br>Many others;<br>classification varies</center></div> }} '''Protists''' ({{IPAEng|ˈproʊtɨst}}), are a diverse group of [[eukaryote|eukaryotic]] [[microorganism]]s. Historically, protists were treated as the [[kingdom (biology)|kingdom]] '''Protista''' but this group is no longer recognized in modern taxonomy. The protists do not have much in common besides a relatively simple organization -- either they are [[unicellular]], or they are [[multicellular]] without specialized [[tissue (biology)|tissues]]. This simple cellular organization distinguishes the protists from other eukaryotes, such as [[fungi]], [[animal]]s and [[plant]]s. The term ''protista'' was first used by [[Ernst Haeckel]] in [[1866]]. Protists were traditionally subdivided into several groups based on similarities to the "higher" kingdoms: the [[one-celled]] animal-like [[protozoa]], the plant-like [[protophyta]] (mostly [[one-celled]] [[algae]]), and the fungus-like [[slime mold]]s and [[water mold]]s. Because these groups often overlap, they have been replaced by [[phylogenetic]]-based [[classification]]s. However, they are still useful as informal names for describing the [[morphology (biology)|morphology]] and [[ecology]] of protists. Protists live in almost any environment that contains liquid water. Many protists, such as the [[algae]], are [[photosynthesis|photosynthetic]] and are vital [[primary producer]]s in ecosystems, particularly in the ocean as part of the [[plankton]]. Other protists, such as the [[Kinetoplastid]]s and [[Apicomplexa]] are responsible for a range of serious human diseases, such as [[malaria]] and [[sleeping sickness]]. ==Classification== ===Historical classifications=== The first division of the protists from other organisms came in the 1820's, when the German biologist Georg A. Goldfuss interoduced the word ''[[protozoa]]'' to refer to organisms such as [[ciliate]]s and [[coral]]s.<ref name=Scamardella1999>{{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}}</ref> This group was expanded in 1845 to include all "unicellular animals", such as [[Foraminifera]] and [[amoebae]]. The formal taxonomic category ''Protoctista'' was first proposed in the early 1860's [[John Hogg (biologist)|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.<ref name=Scamardella1999/> The kingdom of minerals was later removed from taxonomy by [[Ernst Haeckel]], leaving plants, animals, and the protists as a “kingdom of primitive forms”.<ref name=Rothschild1989>{{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}}</ref> 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]] [[eukaryote]]s such as [[diatom]]s, [[green algae]] and [[fungi]].<ref name=Copeland1938>{{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}}</ref> This classification was the basis for Whittaker's later definition of [[Fungi]], [[Animalia]], [[Plantae]] and Protista as the four kingdoms of life.<ref name=Whittaker1959>{{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}}</ref> The kingdom Protista was later modified to separate [[prokaryote]]s into the separate kingdom of [[Monera]], leaving the protists as a group of eukaryotic microorganisms.<ref>{{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}}</ref> These five kingdoms remained the accepted classification until the development of [[molecular phylogenetic]]s in the late 20th century, when it became apparent that neither protists or monera were single groups of related organisms (they were not [[Clade|monophyletic groups]]). ===Modern classifications=== 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.<ref name="Adl 05">{{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}}</ref> The term ''protozoa'' is used to refer to [[heterotroph]]ic 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 [[monophyly|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)<ref name="Adl 05"/> 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.<ref name="Cavalier Smith 03">{{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}}</ref> Many are thought to be monophyletic, though there is still uncertainty. For instance, the [[excavate]]s are probably not monophyletic and the [[chromalveolate]]s are probably only monophyletic if the [[haptophyte]]s and [[cryptomonad]]s are excluded.<ref>{{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}}</ref> ==Types of protists== ===Protozoa, the animal-like protists=== Protozoa are mostly single-celled, [[motile]] protists 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 [[locomotion]] into: {|cellpadding="5" | [[Flagellate]]s || with long [[flagellum|flagella]] || e.g., ''[[Euglena]]'' |- | [[Amoeboid]]s ||with transient [[pseudopod]]ia || e.g., ''[[Amoeba]]'' |- | [[Ciliate]]s || with multiple, short [[cilium|cilia]] || e.g., ''[[Paramecium]]'' |- | [[Apicomplexa|Sporozoa]] || non-mobile parasites; some can form spores || e.g., ''[[Toxoplasma]]'' |} ===Algae, the plant-like protists=== They include many single-celled organisms that are also considered protozoa, such as ''[[Euglena]]'', which many believe have acquired [[chloroplast]]s through secondary [[endosymbiosis]]. Others are non-motile, and some (called [[seaweed]]s) are truly multicellular, including members of the following groups: {|cellpadding="5" | [[Green alga|Chlorophyte]]s || green algae, are related to higher plants || e.g., ''[[sea lettuce|Ulva]]'' |- | [[Red alga|Rhodophyte]]s || red algae || e.g., ''[[Porphyra]]'' |- | [[Heterokont]]ophytes || brown algae, diatoms, etc. || e.g., ''[[Macrocystis]]'' |} The green and red algae, along with a small group called the [[glaucophyte]]s, appear to be close relatives of other plants, and so some authors treat them as Plantae despite their simple organization. Most other types of algae, however, developed separately. They include the [[haptophyte]]s, [[cryptomonad]]s, [[dinoflagellate]]s, [[euglenid]]s, and [[chlorarachniophyte]]s, all of which have also been considered protozoans. Note some protozoa host endosymbiotic algae, as in ''[[Paramecium bursaria]]'' or [[radiolaria]]ns, that provide them with energy but are not integrated into the cell. ===Fungus-like protists=== Various organisms with a protist-level organization were originally treated as fungi, because they produce [[sporangia]]. These include [[Chytridiomycetes|chytrids]], [[slime mold]]s, [[water mold]]s, and [[Labyrinthulomycetes]]. Of these, the chytrids are now known to be related to other fungi and are usually classified with them. The others are now placed among the [[heterokont]]s (which have [[cellulose]] rather than [[chitin]] walls) and the [[Amoebozoa]] (which do not have cell walls). == Metabolism == Protists obtain nutrients and digest nutrients in a complex acquirement and assimilation system. Many protists also feed on [[bacteria]], these organisms engulf food and digest it internally. They extend their [[cell wall]] and [[cell membrane]] around the food material to form a [[vacuole|food vacuole]]. This is then taken into the cell via [[endocytosis]] (usually [[phagocytosis]]; sometimes [[pinocytosis]]). Nutrition in some different types of protists is variable. In flagellates, for example, [[filter feeding]] may sometimes occur where the flagella find the prey. {|class="wikitable" style="margin-left: auto; margin-right: auto;" |+ Nutritional types in protist metabolism |- !Nutritional type !Source of energy !Source of carbon !Examples |- |&nbsp;[[Phototroph]]s&nbsp; |align="center" |&nbsp;Sunlight&nbsp; |align="center" |&nbsp;Organic compounds or carbon fixation |&nbsp;[[Algae]], [[Dinoflagellate]]s or [[Euglena]]&nbsp; |- |&nbsp;[[Organotroph]]s |align="center" |&nbsp;Organic compounds&nbsp; |align="center" |&nbsp;Organic compounds or carbon fixation&nbsp; |&nbsp;''[[Apicomplexa]]'', ''[[Trypanosomes]]'' or ''[[Amoeboid|Amoebae]]''&nbsp; |} ==Reproduction== Some protists reproduce [[sexual reproduction|sexually]], while others reproduce [[asexual reproduction|asexually]]. Some species, for example ''[[Plasmodium falciparum]]'', have extremely complex [[biological life cycle|life cycles]] that involve multiple forms of the organism, some of which reproduce sexually and others asexually.<ref>{{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}}</ref> 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.<ref>{{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}}</ref> ==See also== *[[Prasiola]] ==References== <references /> {{commonscat|Protista}} ==Further reading== 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 [[Category:Eukaryotes]] [[Category:Protista|*]] [[ar:طلائعيات]] [[bg:Протисти]] [[ca:Protista]] [[cs:Protisté]] [[cy:Protist]] [[da:Protist]] [[de:Protisten]] [[et:Protistid]] [[el:Πρώτιστα]] [[es:Protista]] [[eo:Protistoj]] [[eu:Protista]] [[fa:آغازیان]] [[fr:Protista]] [[ga:Prótaisteach]] [[ko:원생생물]] [[hr:Protisti]] [[id:Protista]] [[is:Frumvera]] [[it:Protista]] [[he:פרוטיסטים]] [[lb:Protisten]] [[lt:Pirmuonys]] [[hu:Véglények]] [[mk:Протиста]] [[ms:Protis]] [[nl:Protisten]] [[ja:原生生物]] [[no:Protoktister]] [[oc:Protista]] [[nds:Protisten]] [[pl:Protisty]] [[pt:Protista]] [[ro:Regn Protozoa]] [[qu:Ch'ulla kawsaykuq]] [[ru:Протисты]] [[simple:Protist]] [[sk:Protista]] [[sl:Protisti]] [[sr:Протисти]] [[fi:Alkueliöt]] [[sv:Protister]] [[th:โพรทิสต์]] [[to:Meʻamoʻuimuʻa]] [[tr:Protistler]] [[uk:Найпростіші]] [[zh:原生生物]]