{{otheruses}}
{{Taxobox|
| name = ''Amoeba''
| image = Chaos diffluens.jpg|200px
| domain = [[Eukaryota]]
| regnum = [[Amoebozoa]]
| phylum = [[Tubuliniea]]
| classis = Tubulinida
| familia = [[Amoebidae]]
| genus = '''''Amoeba'''''
| genus_authority = Bery de St. Vincent 1822
}}

'''''Amoeba''''' (sometimes '''''amœba''''' or '''''ameba''''', plural '''''amoebae''''') is a [[genus]] of [[protozoa]] that moves by means of [[pseudopod]]s, and is well-known as a representative [[Microorganism|unicellular organism]]. The word '''amoeba''' or '''ameba''' is variously used to refer to it and its close relatives, now grouped as the [[Amoebozoa]], or to all protozoa that move using pseudopods, otherwise termed [[amoeboid]]s. The amoeba was first discovered by [[August Johann Rösel von Rosenhof]] in 1755.<ref>{{cite journal | last = Leidy | first = Joseph | title = Amoeba proteus | journal = The American Naturalist | volume = 12 | issue = 4 | year = 1878 | pages = 235-238 | url = http://links.jstor.org/sici?sici=0003-0147%28187804%2912%3A4%3C235%3AAP%3E2.0.CO%3B2-7 | accessdate = 2007-06-20}}</ref> Early naturalists referred to ''Amoeba'' as the ''Proteus animalcule'' after the [[Greek mythology|Greek]] god [[Proteus]] who could change his shape. The name "amibe" was given to it by Bery St. Vincent, from the Greek ''amoibè'', meaning change.<ref name = EOS1>{{cite book | first = Kimberley | last = McGrath | coauthors = Blachford, Stacey (eds.) | title = Gale Encyclopedia of Science Vol. 1: Aardvark-Catalyst (2nd ed.) | year = 2001 | isbn = 078764370X | publisher = Gale Group}}</ref>

==Habitat and uses==
''Amoeba'' itself is found in decaying [[vegetation]] in [[Fresh water|fresh]] and [[Saline water|salt]] water, wet soil, and animals.<ref name = EOS1/> Due to the ease with which they may be obtained and kept alive, they are common objects of study as representative protozoa and to demonstrate cell structure and function.

==Anatomy==
The cell's [[organelle]]s and [[cytoplasm]] are enclosed by a [[cell membrane]], obtaining its food through [[phagocytosis]]. Amoebae have a single large tubular [[pseudopod]] at the [[Anatomical terms of location|anterior]] end, and several secondary ones branching to the sides. The most famous species, ''[[Amoeba proteus]]'', is 700-800 [[Micrometre|μm]] in length but the species ''[[Amoeba dubia]]'' is as large as a millimeter, and visible to the naked eye. Its most recognizable features include a single [[cell nucleus|nucleus]] and a simple contractile [[vacuole]] to maintain [[osmosis|osmotic]] pressure. Food enveloped by the amoeba is stored and digested in vacuoles. Amoebae reproduce through [[binary fission]]. In cases where the amoeba are forcibly divided, the portion that retains the nucleus will survive and form a new cell and cytoplasm, while the other portion dies.<ref name = SC>{{cite web | url = http://www.scienceclarified.com/Al-As/Amoeba.html | language = english | format = html | publisher = Scienceclarified.com | title = Amoeba | accessdate = 2007-11-06 }}</ref>

== Reaction to stimuli ==
=== Hypertonic and hypotonic solutions ===
Like most cells, amoebae are adversely affected by excessive [[Osmosis|osmotic pressure]] caused by extremely saline or dilute water. Amoebae will prevent the influx of salt in saline water, resulting in a net loss of water as the cell becomes [[isotonic]] with the environment, causing the cell to shrink. Placed into [[fresh water]], amoebae will also attempt to match the concentration of the surrounding water, causing the cell to swell and sometimes burst.<ref name=Patterson1981>{{cite journal | author = Patterson, D.J. | year = 1981 | title = Contractile vacuole complex behaviour as a diagnostic character for free living amoebae | journal = Protistologica | volume = 17 | pages = 243-248}}</ref> Adjusting the tonicity of the cytoplasm can also damage the digestive enzymes used in phagocytosis, allowing the amoeba to ingest food but not extract energy, resulting in death.<ref name = EOS1/>

=== Amoebic cysts ===
{{main|Microbial cyst}}
In environments which are potentially lethal to the cell, some amoeba may become [[Dormancy|dormant]] by forming itself into a ball and secreting a protective membrane to become a [[Microbial cyst|cyst]]; the cell remains in this state until it encounters more favourable conditions.<ref name = SC/> While in cyst form the amoeba will not replicate and may die if unable to emerge for a lengthy period of time.

=== Marine amoeba ===
Marine amoeba lack contractile vacuoles and their [[enzyme]]s and organelles are not damaged by the salt water found in seas, oceans, salt swamps, salty rivers and ponds.

== Amoebas pathogenic to humans ==
*''[[Entamoeba histolytica]]''
*''[[Naegleria fowleri]]''
*''[[Acanthamoeba]]''
*''[[Balamuthia mandrillaris]]''
*''[[Hartmannella]]''

==References==
{{Reflist}}

==External links==
* [http://tolweb.org/notes/?note_id=51 Amoebae: Protists Which Move and Feed Using Pseudopodia, David Patterson (Tree of Life)]
* [http://wikibooks.org/wiki/Biology_Cell_biology_Introduction_Cell_size Wikibooks: compare size of cells]
* [http://www.bairbrepaws.com/psneeley/FwrPLA.htm Joseph Leidy's Amoeba Plates]

[[Category:Protista]]
[[Category:Amoeboids]]
[[Category:Amoebozoa]]

[[ar:أميبا (كائن دقيق)]]
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