amoeba


amoeba
/euh mee"beuh/, n., pl. amoebas, amoebae /-bee/.
ameba.

* * *

One-celled protozoan that can form temporary extensions of cytoplasm (pseudopodia) in order to move about.

Some amoebas are found on the bottom of freshwater streams and ponds. Others live in the human digestive system; one type causes amebic dysentery in humans. Each amoeba contains a small mass of jellylike cytoplasm with vacuoles and a nucleus. Food is taken in and material is excreted at any point on the cell surface. Amoebas are used extensively in cell research for determining the relative functions and interactions of the nucleus and the cytoplasm.

Amoeba (magnified).

Russ Kinne/Photo Researchers

* * *

▪ protozoan order
also spelled  ameba , plural  amoebas  or  amoebae 
  any of the microscopic unicellular protozoans of the rhizopodan order Amoebida. The well-known type species, Amoeba proteus, is found on decaying bottom vegetation of freshwater streams and ponds. There are numerous parasitic amoebas. Of six species found in the human alimentary tract, Entamoeba histolytica causes amebic dysentery. Two related free-living genera of increasing biomedical importance are Acanthamoeba and Naegleria, strains of which have been recognized as disease-causing parasites in several vertebrates, including humans.

      Amoebas are identified by their ability to form temporary cytoplasmic extensions called pseudopodia (pseudopodium), or false feet, by means of which they move about. This type of movement, called amoeboid movement, is considered to be the most primitive form of animal locomotion.

      Amoebas are used extensively in cell research for determining the relative functions and interactions of the nucleus and the cytoplasm. Each amoeba contains a small mass of jellylike cytoplasm, which is differentiated into a thin outer plasma membrane, a layer of stiff, clear ectoplasm just within the plasma membrane, and a central granular endoplasm. The endoplasm contains food vacuoles, a granular nucleus, and a clear contractile vacuole. The amoeba has no mouth or anus; food is taken in and material excreted at any point on the cell surface. During feeding, extensions of cytoplasm flow around food particles, surrounding them and forming a vacuole into which enzymes are secreted to digest the particles. Oxygen diffuses into the cell from the surrounding water, and metabolic wastes diffuse from the amoeba into the surrounding water. A contractile vacuole, which removes excess water from the amoeba, is absent in most marine and parasitic species. Reproduction is asexual (binary fission).

      During adverse environmental periods many amoebas survive by encystment: the amoeba becomes circular, loses most of its water, and secretes a cyst membrane that serves as a protective covering. When the environment is again suitable, the envelope ruptures, and the amoeba emerges.

* * *


Universalium. 2010.

Look at other dictionaries:

  • Amoeba — Разработчик Эндрю Таненбаум Последняя версия 5.3 12 февраля 2001 Тип ядра Микроядро Лицензия MIT Состояние Остановлен Веб сайт …   Википедия

  • Amoeba — Saltar a navegación, búsqueda Amoeba se puede referir: Amoeba, Sistema Operativo Distribuido. Amoeba, género de protistas. Obtenido de Amoeba Categoría: Wikipedia:Desambiguación …   Wikipedia Español

  • Amoeba — bezeichnet eine Gattung der Amöben, siehe Amoeba (Gattung) ein Betriebssystem, siehe Amoeba (Betriebssystem) Diese Seite ist eine Begriffsklärung zur Unterscheidung mehrerer mit demselben Wort bezeichneter Begriffe …   Deutsch Wikipedia

  • Amoeba — Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. Amibe Amoeba : Système d exploitation distribué développé en 1981 à l Université libre d Amsterdam par Andrew Tanenbaum. Ce document provient de «… …   Wikipédia en Français

  • amoeba — [ə mē′bə] n. pl. amoebas or amoebae [ə mē′bē] [ModL < Gr amoibē, change < ameibein, to change] 1. a one celled, microscopic organism belonging to any of several families of rhizopods that move and feed using pseudopodia and reproduce by… …   English World dictionary

  • Amoeba — A*moe ba, Amoeba A*m[oe] ba, n.; pl. L. {Am[oe]b[ae]}; E. {Am[oe]bas}. [NL., fr. Gr. ? change.] (Zo[ o]l.) A rhizopod common in fresh water, capable of undergoing many changes of form at will. Same as {ameba}. See {Rhizopoda}. [1913 Webster] || …   The Collaborative International Dictionary of English

  • Amoeba — A*moe ba, Amoeba A*m[oe] ba, n.; pl. L. {Am[oe]b[ae]}; E. {Am[oe]bas}. [NL., fr. Gr. ? change.] (Zo[ o]l.) A rhizopod common in fresh water, capable of undergoing many changes of form at will. Same as {ameba}. See {Rhizopoda}. [1913 Webster] || …   The Collaborative International Dictionary of English

  • amoeba — см. Приложение 1 (Amoeba). (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • amoeba — (n.) 1855, from Mod.L. Amoeba, genus name (1841), from Gk. amoibe change, related to ameibein to change, exchange, from PIE *e meigw , extended form of root *mei to change, go, move (see MUTABLE (Cf. mutable)). So called for its constantly… …   Etymology dictionary

  • amoeba — amoeba. См. амебы. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • amoebă — s.f. v. amibă. Trimis de LauraGellner, 13.09.2007. Sursa: DN …   Dicționar Român


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.