Editing Microorganism (section)

==Classification and structure==
Microorganisms can be found almost anywhere on [[Earth]]. [[Bacteria]] and [[archaea]] are almost always microscopic, while a number of [[eukaryote]]s are also microscopic, including most [[Protista|protists]], some [[fungus|fungi]], as well as some [[micro-animal]]s and plants. [[Virus]]es are generally regarded as [[Non-cellular life|not living]] and therefore not considered to be microorganisms, although a subfield of [[microbiology]] is [[virology]], the study of viruses.<ref>{{Cite book |title=eLS|last=Lim|first=Daniel V. |date=2001 |publisher=John Wiley |isbn=978-0-470-01590-2 |doi=10.1038/npg.els.0000459|chapter = Microbiology}}</ref><ref>{{Cite web|url=http://www.highveld.com/microbiology/what-is-microbiology.html|title=What is Microbiology? |website=highveld.com |access-date=2017-06-02|archive-url=https://web.archive.org/web/20150215180557/http://www.highveld.com/microbiology/what-is-microbiology.html |archive-date=2015-02-15}}</ref><ref>{{cite book |last=Cann |first=Alan |title=Principles of Molecular Virology |year=2011 |publisher=Academic Press |isbn=978-0-12-384939-7 |edition=5th}}</ref>

===Evolution===
{{further|Timeline of the evolutionary history of life|Earliest known life forms}}
{{PhylomapB||caption=[[Carl Woese]]'s 1990 [[phylogenetic tree]] based on [[rRNA]] data shows the domains of [[Bacteria]], [[Archaea]], and [[Eukaryota]]. All are microorganisms except some eukaryote groups.|size=325px}}
Single-celled microorganisms were the [[Origin of life|first forms of life]] to develop on Earth, approximately 3.5 billion years ago.<ref>{{Cite journal |author=Schopf, J. |title=Fossil evidence of Archaean life |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=869–885 |year=2006 |pmid=16754604 |doi=10.1098/rstb.2006.1834 |pmc=1578735}}</ref><ref>{{Cite journal |last=Altermann |first=W. |last2=Kazmierczak |first2=J. |title=Archean microfossils: a reappraisal of early life on Earth |journal=Res Microbiol |volume=154 |issue=9 |pages=611–617 |year=2003 |pmid=14596897 | doi=10.1016/j.resmic.2003.08.006|doi-access=free }}</ref><ref>{{Cite journal|last=Cavalier-Smith |first=T. |author-link=Thomas Cavalier-Smith |title=Cell evolution and Earth history: stasis and revolution  |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=969–1006 |year=2006 |pmid=16754610 |doi=10.1098/rstb.2006.1842 |pmc=1578732}}</ref> Further evolution was slow,<ref>{{Cite journal| last=Schopf |first=J. | title=Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic | pmc=44277| journal=PNAS | volume=91 | issue=15 | pages=6735–6742 | year=1994 | pmid=8041691 | doi=10.1073/pnas.91.15.6735 | bibcode=1994PNAS...91.6735S| doi-access=free }}</ref> and for about 3&nbsp;billion years in the [[Precambrian]] [[Eon (geology)|eon]], (much of the history of [[life|life on Earth]]), all [[organism]]s were microorganisms.<ref>{{Cite journal|author=Stanley, S. |title=An Ecological Theory for the Sudden Origin of Multicellular Life in the Late Precambrian |journal=PNAS |volume=70 |issue=5 |pages=1486–1489 |date=May 1973 |pmid=16592084 |pmc=433525 | doi=10.1073/pnas.70.5.1486 |bibcode=1973PNAS...70.1486S |doi-access=free }}</ref><ref>{{Cite journal |author1=DeLong, E. |author2=Pace, N. | title=Environmental diversity of bacteria and archaea | journal=Syst Biol | volume=50 | issue=4 | pages=470–478 | year=2001 |pmid=12116647 | doi=10.1080/106351501750435040|citeseerx=10.1.1.321.8828 }}</ref> Bacteria, algae and fungi have been identified in [[amber]] that is 220&nbsp;million years old, which shows that the [[Morphology (biology)|morphology]] of microorganisms has changed little since at least the [[Triassic]] period.<ref>{{Cite journal |author=Schmidt, A. |author2=Ragazzi, E. |author3=Coppellotti, O. |author4=Roghi, G. | title=A microworld in Triassic amber | journal=Nature | volume=444 | issue=7121 | page=835 | year=2006 | pmid=17167469 | doi=10.1038/444835a |bibcode=2006Natur.444..835S |s2cid=4401723 | doi-access=free }}</ref> The newly discovered [[Nickel#Biological role|biological role played by nickel]], however – especially that brought about by [[Types of volcanic eruption|volcanic eruptions]] from the [[Siberian Traps]] – may have accelerated the evolution of [[methanogen]]s towards the end of the [[Permian–Triassic extinction event]].<ref>{{cite web |url= http://www.space.com/26654-microbe-innovation-started-largest-earth-extinction.html |title= Microbe's Innovation May Have Started Largest Extinction Event on Earth |last= Schirber |first=Michael |date= 27 July 2014 |publisher=Astrobiology Magazine |website= Space.com |quote=That spike in nickel allowed methanogens to take off.}}</ref>

Microorganisms tend to have a relatively fast rate of evolution. Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through [[Bacterial conjugation|conjugation]], [[Transformation (genetics)|transformation]] and [[Transduction (genetics)|transduction]], even between widely divergent species.<ref>{{Cite journal| author=Wolska, K. | title=Horizontal DNA transfer between bacteria in the environment | journal=Acta Microbiol Pol | volume=52 | issue=3 | pages=233–243 | year=2003 |pmid=14743976}}</ref> This [[horizontal gene transfer]], coupled with a high [[mutation]] rate and other means of transformation, allows microorganisms to swiftly [[biological evolution|evolve]] (via [[natural selection]]) to survive in new environments and respond to [[stressors|environmental stresses]]. This rapid evolution is important in medicine, as it has led to the development of [[multidrug resistance|multidrug resistant]] [[pathogenic bacteria]], ''superbugs'', that are [[antimicrobial resistance|resistant to antibiotics]].<ref>{{Cite journal |author=Enright, M. |author2=Robinson, D. |author3=Randle, G. |author4=Feil, E. |author5=Grundmann, H. |author6=Spratt, B. | title=The evolutionary history of methicillin-resistant ''Staphylococcus aureus'' (MRSA) | journal=Proc Natl Acad Sci USA | volume=99 | issue=11 | pages=7687–7692 |date=May 2002 | pmid=12032344 |pmc=124322 | doi=10.1073/pnas.122108599|bibcode=2002PNAS...99.7687E |doi-access=free }}</ref>

A possible transitional form of microorganism between a prokaryote and a eukaryote was discovered in 2012 by Japanese scientists. ''[[Parakaryon myojinensis]]'' is a unique microorganism larger than a typical prokaryote, but with nuclear material enclosed in a membrane as in a eukaryote, and the presence of endosymbionts. This is seen to be the first plausible evolutionary form of microorganism, showing a stage of development from the prokaryote to the eukaryote.<ref name="Parakaryon">{{cite web |title=Deep sea microorganisms and the origin of the eukaryotic cell |url=http://protistology.jp/journal/jjp47/JJP47YAMAGUCHI.pdf |access-date=24 October 2017}}</ref><ref name="Yamaguchi">{{cite journal|last1=Yamaguchi |display-authors=et al|first1=Masashi |title=Prokaryote or eukaryote? A unique microorganism from the deep sea |issue=6 |journal=Journal of Electron Microscopy |volume=61 |pages=423–431 |doi=10.1093/jmicro/dfs062 |pmid=23024290 |date=1 December 2012}}</ref>

===Archaea===
{{main|Archaea}}
{{further|Prokaryote}}

Archaea are [[prokaryote|prokaryotic]] unicellular organisms, and form the first domain of life in [[Carl Woese]]'s [[three-domain system]]. A prokaryote is defined as having no [[cell nucleus]] or other [[lipid bilayer|membrane bound]]-[[organelle]]. Archaea share this defining feature with the bacteria with which they were once grouped. In 1990 the microbiologist Woese proposed the three-domain system that divided living things into bacteria, archaea and eukaryotes,<ref>{{Cite journal |author1=Woese, C. |author1-link=Carl Woese | author2=Kandler, O. | author3=Wheelis, M. | title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya | doi= 10.1073/pnas.87.12.4576 | journal=Proc Natl Acad Sci USA | volume=87 | issue=12 | pages=4576–4579 | year=1990 | pmid=2112744 | pmc=54159 | bibcode=1990PNAS...87.4576W|doi-access=free }}</ref> and thereby split the prokaryote domain.

Archaea differ from bacteria in both their genetics and biochemistry. For example, while bacterial [[cell membrane]]s are made from [[phospholipid|phosphoglycerides]] with [[ester]] bonds, Achaean membranes are made of [[ether lipid]]s.<ref>{{Cite journal |author1=De Rosa, M. |author2=Gambacorta, A. | author3=Gliozzi, A. |title=Structure, biosynthesis, and physicochemical properties of archaebacterial lipids |journal=Microbiol. Rev. |volume=50 |issue=1 |pages=70–80 |date=1 March 1986|pmid=3083222 |pmc=373054 |doi=10.1128/mmbr.50.1.70-80.1986}}</ref> Archaea were originally described as [[extremophile]]s living in [[extreme environment]]s, such as [[hot spring]]s, but have since been found in all types of [[habitat]]s.<ref>{{Cite journal |author1=Robertson, C. |author2=Harris, J. |author3=Spear, J. |author4=Pace, N. | title=Phylogenetic diversity and ecology of environmental Archaea | journal=Curr Opin Microbiol | volume=8 | issue=6 | pages=638–642 | year=2005 | pmid=16236543 | doi=10.1016/j.mib.2005.10.003}}</ref> Only now are scientists beginning to realize how common archaea are in the environment, with [[Thermoproteota]] (formerly Crenarchaeota) being the most common form of life in the ocean, dominating ecosystems below {{convert|150|m}} in depth.<ref>{{Cite journal |author=Karner, M. B. |author2=DeLong, E. F. |author3=Karl, D. M. |title=Archaeal dominance in the mesopelagic zone of the Pacific Ocean |journal=Nature |volume=409 |issue=6819 |pages=507–510 |year=2001 |pmid=11206545 | doi=10.1038/35054051|bibcode=2001Natur.409..507K |s2cid=6789859 }}</ref><ref>{{Cite journal |author=Sinninghe Damsté, J. S. |author2=Rijpstra, W. I. |author3=Hopmans, E. C. |author4=Prahl, F. G. |author5=Wakeham, S. G. |author6=Schouten, S. |title=Distribution of Membrane Lipids of Planktonic Crenarchaeota in the Arabian Sea |journal=Appl. Environ. Microbiol. |volume=68 |issue=6 |pages=2997–3002 |date=June 2002 |pmid=12039760 |pmc=123986 | doi=10.1128/AEM.68.6.2997-3002.2002|bibcode=2002ApEnM..68.2997S }}</ref> These organisms are also common in soil and play a vital role in [[ammonia]] oxidation.<ref name=LeiningerUrich2006>{{cite journal |last1=Leininger |first1=S. |last2=Urich |first2=T. |last3=Schloter |first3=M. |last4=Schwark |first4=L.|last5=Qi|first5=J. |last6=Nicol |first6=G. W. |last7=Prosser |first7=J. I. |author-link7=James I. Prosser |last8=Schuster |first8=S. C. |last9=Schleper |first9=C.|title=Archaea predominate among ammonia-oxidizing prokaryotes in soils |journal=[[Nature (journal)|Nature]] |volume=442 |issue=7104 |year=2006|pages=806–809|pmid= 16915287 |doi=10.1038/nature04983|bibcode=2006Natur.442..806L|s2cid=4380804 }}</ref>

The combined domains of archaea and bacteria make up the most diverse and abundant group of [[organism]]s on Earth and inhabit practically all environments where the temperature is below +{{convert|140|°C}}. They are found in [[water]], [[soil]], [[Earth's atmosphere|air]], as the [[microbiome]] of an organism, [[hot spring]]s and even deep beneath the Earth's crust in [[Rock (geology)|rocks]].<ref name=Gold>{{Cite journal|author=Gold, T. |title=The deep, hot biosphere |journal=Proc. Natl. Acad. Sci. USA |volume=89 |issue=13 |pages=6045–6049 |year=1992 |pmid=1631089 |doi= 10.1073/pnas.89.13.6045 |pmc=49434 |bibcode=1992PNAS...89.6045G|doi-access=free }}</ref> The number of prokaryotes is estimated to be around five nonillion, or 5 × 10<sup>30</sup>, accounting for at least half the [[Biomass (ecology)|biomass]] on Earth.<ref>{{Cite journal|author=Whitman, W. |author2=Coleman, D. |author3=Wiebe, W. | title=Prokaryotes: The unseen majority | doi= 10.1073/pnas.95.12.6578 | journal=PNAS | volume=95 | issue=12 | pages=6578–6583 | year=1998 | pmid=9618454 | pmc=33863|bibcode=1998PNAS...95.6578W |doi-access=free }}</ref>

The biodiversity of the prokaryotes is unknown, but may be very large. A May 2016 estimate, based on laws of scaling from known numbers of species against the size of organism, gives an estimate of perhaps 1&nbsp;trillion species on the planet, of which most would be microorganisms. Currently, only one-thousandth of one percent of that total have been described.<ref name="NSF-2016002">{{cite news |title=Researchers find that Earth may be home to 1 trillion species |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=138446 |date=2 May 2016 |work=[[National Science Foundation]] |access-date=6 May 2016 }}</ref> [[Archaea|Archael cells]] of some species aggregate and transfer [[DNA]] from one cell to another through direct contact, particularly under stressful environmental conditions that cause [[DNA damage (naturally occurring)|DNA damage]].<ref>{{cite journal |last1=van Wolferen |first1=M.|last2=Wagner |first2=A|last3=van der Does |first3=C.|last4=Albers |first4=S. V. | year = 2016 | title = The archaeal Ced system imports DNA | journal = Proc Natl Acad Sci USA | volume = 113 | issue = 9| pages = 2496–501 | doi = 10.1073/pnas.1513740113 | pmid = 26884154 | pmc = 4780597 | bibcode = 2016PNAS..113.2496V | doi-access = free }}</ref><ref>Bernstein H, Bernstein C. Sexual communication in archaea, the precursor to meiosis. pp. 103–117 in Biocommunication of Archaea (Guenther Witzany, ed.) 2017. Springer International Publishing {{ISBN|978-3-319-65535-2}} DOI 10.1007/978-3-319-65536-9</ref>

===Bacteria===
{{Main|Bacteria}}
[[File:Staphylococcus aureus 01.jpg|thumb|''[[Staphylococcus aureus]]'' bacteria magnified about 10,000×]]
Like archaea, bacteria are prokaryotic – unicellular, and having no cell nucleus or other membrane-bound organelle. Bacteria are microscopic, with a few extremely rare exceptions, such as ''[[Thiomargarita namibiensis]]''.<ref>{{Cite journal |last=Schulz |first=H. |last2=Jorgensen |first2=B. | title=Big bacteria | journal=Annu Rev Microbiol | volume=55 | pages=105–137 | year =2001 |pmid=11544351 | doi=10.1146/annurev.micro.55.1.105}}</ref> Bacteria function and reproduce as individual cells, but they can often aggregate in multicellular [[Colony (biology)#Microbial colony|colonies]].<ref>{{Cite journal |author-link=James A. Shapiro |last=Shapiro |first=J. A. |title=Thinking about bacterial populations as multicellular organisms |journal=Annu. Rev. Microbiol. |volume=52 |pages=81–104 |year=1998 |pmid=9891794 |doi=10.1146/annurev.micro.52.1.81 |url=http://www.sci.uidaho.edu/newton/math501/Sp05/Shapiro.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110717183759/http://www.sci.uidaho.edu/newton/math501/Sp05/Shapiro.pdf |archive-date=17 July 2011 }}</ref> Some species such as [[myxobacteria]] can aggregate into complex [[swarm]]ing structures, operating as multicellular groups as part of their [[Biological life cycle|life cycle]],<ref>{{cite journal | title=Myxobacteria: Moving, Killing, Feeding, and Surviving Together | journal=Frontiers in Microbiology| volume=7| page=781| pmid=27303375| pmc=4880591| year=2016| last1=Muñoz-Dorado| first1=J. | last2=Marcos-Torres| first2=F. J. | last3=García-Bravo | first3=E. | last4=Moraleda-Muñoz| first4=A. | last5=Pérez| first5=J. | doi=10.3389/fmicb.2016.00781| doi-access=free}}</ref> or form clusters in [[colony (biology)|bacterial colonies]] such as ''[[E. coli]]''.

Their [[genome]] is usually a [[circular bacterial chromosome]] – a single loop of [[DNA]], although they can also harbor small pieces of DNA called [[plasmid]]s. These plasmids can be transferred between cells through [[bacterial conjugation]]. Bacteria have an enclosing [[Bacterial cell structure#Cell wall|cell wall]], which provides strength and rigidity to their cells. They reproduce by [[binary fission]] or sometimes by [[budding]], but do not undergo [[Meiosis|meiotic]] [[sexual reproduction]]. However, many bacterial species can transfer DNA between individual cells by a [[horizontal gene transfer]] process referred to as natural [[Transformation (genetics)|transformation]].<ref>{{cite journal |last=Johnsbor |first=O. |last2=Eldholm |first2=V. |last3=Håvarstein |first3=L. S. |title=Natural genetic transformation: prevalence, mechanisms and function |journal=Res. Microbiol. |volume=158 |issue=10 |pages=767–778 |date=December 2007 |pmid=17997281 |doi=10.1016/j.resmic.2007.09.004 |doi-access=free }}</ref> Some species form extraordinarily resilient [[endospore|spores]], but for bacteria this is a mechanism for survival, not reproduction. Under optimal conditions bacteria can grow extremely rapidly and their numbers can double as quickly as every 20 minutes.<ref>{{Cite journal| last=Eagon |first=R. | title=Pseudomonas Natriegens, a Marine Bacterium With a Generation Time of Less Than 10 Minutes | journal=J Bacteriol | volume=83 | issue=4| pages=736–737 | year =1962 | pmid=13888946 | pmc=279347| doi=10.1128/JB.83.4.736-737.1962 }}</ref>

===Eukaryotes===
{{Main|Eukaryote}}

Most living things that are visible to the naked eye in their adult form are [[eukaryote]]s, including [[human]]s. However, many eukaryotes are also microorganisms. Unlike [[bacteria]] and [[archaea]], eukaryotes contain [[organelle]]s such as the [[cell nucleus]], the [[Golgi apparatus]] and [[mitochondrion|mitochondria]] in their [[cell (biology)|cells]]. The nucleus is an organelle that houses the [[DNA]] that makes up a cell's genome. DNA (Deoxyribonucleic acid) itself is arranged in complex [[chromosome]]s.<ref>[http://www.ucmp.berkeley.edu/alllife/eukaryotamm.html Eukaryota: More on Morphology.] (Retrieved 10 October 2006)</ref>
[[Mitochondrion|Mitochondria]] are organelles vital in [[metabolism]] as they are the site of the [[citric acid cycle]] and [[oxidative phosphorylation]]. They evolved from [[symbiotic]] bacteria and retain a remnant genome.<ref name=Dyall>{{Cite journal |author=Dyall, S. |author2=Brown, M. |author3=Johnson, P. | title=Ancient invasions: from endosymbionts to organelles | journal=Science | volume=304 | issue=5668 | pages=253–257 | year=2004|pmid=15073369 | doi=10.1126/science.1094884|bibcode=2004Sci...304..253D |s2cid=19424594 }}</ref> Like bacteria, [[plant cell]]s have [[cell wall]]s, and contain organelles such as [[chloroplast]]s in addition to the organelles in other eukaryotes. Chloroplasts produce energy from light by [[photosynthesis]], and were also originally symbiotic bacteria.<ref name=Dyall/>

Unicellular eukaryotes consist of a single [[Cell (biology)|cell]] throughout their life cycle. This qualification is significant since most [[multicellular organism|multicellular]] eukaryotes consist of a single cell called a [[zygote]] only at the beginning of their life cycles. Microbial eukaryotes can be either [[haploid]] or [[diploid]], and some organisms have multiple [[cell nucleus|cell nuclei]].

Unicellular eukaryotes usually reproduce asexually by [[mitosis]] under favorable conditions. However, under stressful conditions such as nutrient limitations and other conditions associated with DNA damage, they tend to reproduce sexually by [[meiosis]] and [[Fertilization|syngamy]].<ref name=Bernstein>{{cite book |last1=Bernstein |first1=H. |last2=Bernstein |first2=C. |last3=Michod |first3=R. E. |year=2012 |chapter-url=https://www.novapublishers.com/catalog/product_info.php?products_id=31918 |title=DNA repair as the primary adaptive function of sex in bacteria and eukaryotes.  |chapter=Chapter 1 |pages=1–49 |series= DNA Repair: New Research |editor-first1=Sakura |editor-last1=Kimura |editor-first2=Sora |editor-last2=Shimizu |publisher=Nova Sci. Publ. |isbn=978-1-62100-808-8 |url-status=dead |archive-url=https://web.archive.org/web/20180722155931/https://www.novapublishers.com/catalog/product_info.php?products_id=31918 |archive-date= Jul 22, 2018 }}</ref>

====Protists====
{{Main|Protista}}
[[File:Euglena mutabilis - 400x - 1 (10388739803) (cropped).jpg|thumb|upright=0.8|''[[Euglena|Euglena mutabilis]]'', a [[photosynthetic]] [[flagellate]]]]

Of [[Eukaryote|eukaryotic]] groups, the [[protists]] are most commonly [[unicellular]] and microscopic. This is a highly diverse group of organisms that are not easy to classify.<ref>{{Cite journal|author=Cavalier-Smith T |author-link=Thomas Cavalier-Smith |title=Kingdom protozoa and its 18 phyla |journal=Microbiol. Rev. |volume=57 |issue=4 |pages=953–994 |date=1 December 1993|pmid=8302218 |pmc=372943 |doi=10.1128/mmbr.57.4.953-994.1993 |doi-access=free }}</ref><ref>{{Cite journal|last=Corliss |first=J. O. |title=Should there be a separate code of nomenclature for the protists? |journal=BioSystems |volume=28 |issue=1–3 |pages=1–14 |year=1992 |pmid=1292654 | doi=10.1016/0303-2647(92)90003-H|bibcode=1992BiSys..28....1C }}</ref> Several [[algae]] [[species]] are [[multicellular]] protists, and [[slime mold]]s have unique life cycles that involve switching between unicellular, colonial, and multicellular forms.<ref>{{Cite journal|author=Devreotes, P. |title=Dictyostelium discoideum: a model system for cell-cell interactions in development |journal=Science |volume=245 |issue=4922 |pages=1054–1058 |year=1989 |pmid=2672337 | doi=10.1126/science.2672337|bibcode=1989Sci...245.1054D }}</ref> The number of species of protists is unknown since only a small proportion has been identified. Protist diversity is high in oceans, deep sea-vents, river sediment and an acidic river, suggesting that many eukaryotic microbial communities may yet be discovered.<ref>{{Cite journal|author=Slapeta, J. |author2=Moreira, D. |author3=López-García, P. |title=The extent of protist diversity: insights from molecular ecology of freshwater eukaryotes |journal=Proc. Biol. Sci. |volume=272 |issue=1576 |pages=2073–2081 |year=2005 |pmid=16191619 |doi=10.1098/rspb.2005.3195 |pmc=1559898}}</ref><ref>{{Cite journal |author=Moreira, D. |author2=López-García, P. |title=The molecular ecology of microbial eukaryotes unveils a hidden world |journal=Trends Microbiol. |volume=10 |issue=1 |pages=31–38 |year=2002 |pmid=11755083 | url=http://download.bioon.com.cn/view/upload/month_0803/20080326_daa08a6fdb5d38e3a0d8VBrocN3WtOdR.attach.pdf | doi=10.1016/S0966-842X(01)02257-0}}</ref>

====Fungi====
{{Main|Fungus}}

The [[fungus|fungi]] have several unicellular species, such as baker's yeast (''[[Saccharomyces cerevisiae]]'') and fission yeast (''[[Schizosaccharomyces pombe]]''). Some fungi, such as the pathogenic yeast ''[[Candida albicans]]'', can undergo [[phenotypic switching]] and grow as single cells in some environments, and [[Hypha|filamentous hyphae]] in others.<ref>{{Cite journal |author=Kumamoto, C.A. |author-link1=Carol Kumamoto|author2=Vinces, M. D. |title=Contributions of hyphae and hypha-co-regulated genes to Candida albicans virulence |journal=Cell. Microbiol. |volume=7 |issue=11 |pages=1546–1554 |year=2005 |pmid=16207242 | doi=10.1111/j.1462-5822.2005.00616.x|doi-access=free }}</ref>

====Plants====
{{Main|Plant}}

The [[green algae]] are a large group of photosynthetic eukaryotes that include many microscopic organisms. Although some green algae are classified as [[protist]]s, others such as [[charophyta]] are classified with [[embryophyte]] plants, which are the most familiar group of land plants. Algae can grow as single cells, or in long chains of cells. The green algae include unicellular and colonial [[flagellate]]s, usually but not always with two [[flagellum|flagella]] per cell, as well as various colonial, [[Chlorococcales|coccoid]], and filamentous forms. In the [[Charales]], which are the algae most closely related to higher plants, cells differentiate into several distinct tissues within the organism. There are about 6000 species of green algae.<ref>{{Cite book |author=Thomas, David C. |title=Seaweeds |publisher=Natural History Museum |location=London |year=2002 |isbn=978-0-565-09175-0 }}</ref>