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Amoeba
Scientific classification
Domain: Eukaryota
Kingdom: Amoebozoa
Phylum: Tubulinea
Order: Tubulinida
Family: Amoebidae
Genus: Amoeba
Bory de Saint-Vincent, 1822
Species

Amoeba proteus

Amoeba (sometimes amœba or ameba, plural amoebae) is a genus of protozoan.[1]

Contents

Terminology

There are many closely related terms that can be the source of confusion:

  • Amoeba is a genus that includes species such as Amoeba proteus
  • Amoebidae is a family that includes the Amoeba genus, among others.
  • Amoebozoa is a kingdom that includes the Amoebidae family, among others.
  • Amoeboids are organisms that move by crawling. Many (but not all) Amoeboids are Amoebozoa.

History

The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757.[2] Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus who could change his shape. The name "amibe" was given to it by Bory de Saint-Vincent,[3] from the Greek amoibè (αμοιβή), meaning change.[4]

Anatomy

Anatomy of an amoeba

The cell's organelles and cytoplasm are enclosed by a cell membrane, obtaining its food through phagocytosis. Amoebae have a single large tubular pseudopod at the anterior end, and several secondary ones branching to the sides. The most famous species, Amoeba proteus, averages about 220-740 μm in length while moving,[5] making it a giant among amoeboids.[6] A few amoeboids belonging to different genera can grow larger, however, such as Gromia, Pelomyxa, and Chaos.

Amoebae's most recognizable features include one or more nuclei and a simple contractile vacuole to maintain osmotic equilibrium. Food enveloped by the amoeba is stored and digested in vacuoles. Amoebae, like other single-celled eukaryotic organisms, reproduce asexually via mitosis and cytokinesis, not to be confused with binary fission, which is how prokaryotes (bacteria) reproduce. 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. Amoebae also have no definite shape.[7]

Genome

The amoeba is remarkable for its very large genome. The species Amoeba protea has 290 billion base pairs in its genome, while the related Polychaos dubium (formerly known as Amoeba dubia) has 670 billion base pairs. The human genome is small by contrast, with its count of 2.9 billion base pairs.[8]

Reaction to stimuli

Hypertonic and hypotonic solutions

Like most cells, amoebae are adversely affected by excessive 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.[9]

Amoebic cysts

In environments which are potentially lethal to the cell, an amoeba may become dormant by forming itself into a ball and secreting a protective membrane to become a microbial cyst. The cell remains in this state until it encounters more favourable conditions.[7] 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 enzymes and organelles are not damaged by the salt water found in seas, oceans, salt swamps, salty rivers and ponds. Most are microscopic, but some can grow as large as grapes.[10]

References

  1. ^ Amoeba at Dorland's Medical Dictionary
  2. ^ Leidy, Joseph (1878). "Amoeba proteus". The American Naturalist 12 (4): 235–238. doi:10.1086/272082. http://links.jstor.org/sici?sici=0003-0147%28187804%2912%3A4%3C235%3AAP%3E2.0.CO%3B2-7. Retrieved 2007-06-20. 
  3. ^ Audouin, Jean-Victor; et al (1826). Dictionnaire classique d'histoire naturelle. Rey et Gravier. pp. 5. http://books.google.com/books?id=1I8DAAAAQAAJ&pg=PA158&lpg=PA158&dq=%22bory+de+saint+vincent+jean+baptiste+genevieve+marcellin%22+amibe&source=web&ots=SCcqmYPPSy&sig=vje4JuVmdQzWrFqpXTw2UjRsgx8#PPA5,M1. 
  4. ^ McGrath, Kimberley; Blachford, Stacey (eds.) (2001). Gale Encyclopedia of Science Vol. 1: Aardvark-Catalyst (2nd ed.). Gale Group. ISBN 078764370X. OCLC 46337140. 
  5. ^ "Amoeba proteus". Amoebae on the Web. http://amoeba.ifmo.ru/species/amoebidae/aprot.htm. Retrieved 2009-10-08. 
  6. ^ MacIver, Sutherland. "Isolation of Amoebae". The Amoebae. http://www.bms.ed.ac.uk/research/others/smaciver/Protocols/AmoebaProts/isolation_of_amoebae.htm. Retrieved 2009-10-08. 
  7. ^ a b "Amoeba". Scienceclarified.com. http://www.scienceclarified.com/Al-As/Amoeba.html. 
  8. ^ http://www.genomenewsnetwork.org/articles/02_01/Sizing_genomes.shtml
  9. ^ Patterson, D.J. (1981). "Contractile vacuole complex behaviour as a diagnostic character for free living amoebae". Protistologica 17: 243–248. 
  10. ^ https://webspace.utexas.edu/lhc58/protist_slideshow/

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

AMOEBA, the Greek equivalent of the name "Amibe" given by Bery St Vincent to the Proteus animalcule of earlier naturalists, used as a quasi-popular term for any simple naked protist the sole external organs of which are pseudopodia, i.e. temporary outgrowths of the clearer outer layer of the soft protoplasmic body. It is also used as a generic name, and in its present limitations by E. Penard includes only those the pseudopodia of which are constantly changing, blunt outgrowths. In the former wider sense, amoebae are found in sluggish waters, fresh and salt, all over the world; they readily make their appearance in infusions putrefying after infection from aerially carried germs, and the leucocytes or colourless blood corpuscles of Metazoa are essentially amoebae in their structure and behaviour. The protoplasm of the individual is divided into a centrally placed body, the nucleus, of relatively stable shape, and the cytoplasm, itself divided into an outer, clearer ectoplasm ("ectosarc") and an inner, more granular endoplasm ("endosarc"), passing into one another. The movements of amoebae are of several kinds. (1) The amoeba may grow out irregularly into blunt lobes, the pseudopodia, some being emitted while others are retracted, and so may advance in any direction by the emission of pseudopodia thitherward, and the enlargement of these by the passage of the organism into them. (2) Again, it may advance by a sort of rolling: the lower surface, or that in contact with the substratum over or under which it is passing, is viscid and adheres to the substratum, the superficial dorsal layer passing forward and bending over to the ventral side; whilst the converse action takes place at the hinder end; (3) or again, the pseudopodia, when long, well marked and relatively permanent, may serve as actual limbs on which the body is supported and on which it moves. In the outgrowth of a pseudopod the process may take place gradually, the ectoplasm growing as it stretches, or it may take place by the limiting layer of the ectosarc bursting, as it were, and a rounded prominence of the endosarc protruding and at once forming a new "skin" or pellicle. This last mode, termed "eruptive," is common in the case of the enormous, multinucleate amoeba termed Pelomyxa palustris, which attains a diameter when contracted and spherical of as much as a line (over 2 mm.). From the ease with which amoebae are obtained and kept alive under the microscope, as well as from their identity in structure with the primitive elements of Metazoa, they have always been favourite objects of study for protoplasmic physiology under its simplest conditions. Among the investigators of protoplasmic movements we may cite F. Dujardin, O. Biitschli, L. Rhumbler and H. S. Jennings. The opening to the exterior of the contractile vesicle has been found here. Pelomyxa has yielded to A. E. Dixon and M. Hartog a peptic ferment, such as has been extracted by C. F. W. Krukenbergfromthe Myxomycete Fuligo (Flowers of Tan), which is the largest known naked mass of protoplasm without cellular differentiation.

Amoeba shows also the multiplication by fission, so characteristic of the cell: for the study of other modes of reproduction, spore formation and. syngamic (or so-called fertilization) processes, fresh-water or salt-water amoebae are ill suited, and up to this date we do not know the life cycle of any free-living naked amoeba, though that of some parasitic forms and shell-bearers have been fully made out. Some amoebae are certainly young states of Myxomycetes. Encystment, the excretion of a membrane around the cell to tide over unfavourable circumstances, has been noted in almost all species.

Amoeba coli and A. histolytica are parasites in the gut of man, the former relatively harmless, the latter the cause of severe dysentery and hepatic abscess, common in India.

H. S. Jennings has recently made a full study of the movements of Amoeba, and of its general behaviour, and found therein many indications that these are on the whole such as we should expect of an organism working by "trial and error" rather than the uniform modes of non-living beings. Thus the operations of an amoeba ingesting a round, encysted Euglena are summed up thus: "One seems to see that the amoeba is trying to obtain this cyst for food, that it shows remarkable pertinacity in continuing its attempts to put forth efforts to accomplish this in various ways, and that it shows remarkable pertinacity in continuing its attempts to ingest the food when it meets with difficulties. Indeed the scene could be described in a much more vivid and interesting way by the use of terms still more anthropomorphic in tendency." (M. H A.)


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Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Phylum: Amoebozoa
Subphylum: Protamoebae
Classis: Lobosea
Ordo: Euamoebida
Familia: Amoebidae
Genus: Amoeba
Species: A. discoides - A. dubia - A. gorgonia - A. guttula - A. limicola - A. proteus - A. radiosa - A. spumosa - A. striata - A. verrocosa - A. vespertilio

Name

Amoeba Bory de Saint-Vincent, 1822

References

links

Vernacular names

Українська: Амеба
中文: 變形蟲

Simple English

File:Amoeba (PSF).png
Diagram of amoeba structure

Amoeba (plural = amoebae) is well-known as a unicellular organism, a protist. The amoeba was first discovered by August von Rosenhof in 1757.[1] It is a genus of protozoa that moves with false feet, called pseudopodia.

The amoeba is a member of a whole group of amoeboid eukaryotic protists. They are heterotrophs, eating bacteria and other protists.

Contents

Pseudopodia

These are unique extensions of the organism's membrane. They are used by the amoeba for phagocytosis (active food/nutrient intake) and motility (self-propelled movement).

Life

Amoebae are often found within freshwater, typically on vegetation in decay in still or slow moving water, or in the benthic zone of some lakes. However, they are common organisms of study because it is easy to keep them in a laboratory. They are used to study protozoa and to demonstrate cell structure and function.

Other websites

References

  1. Leidy, Joseph (1878). "Amoeba proteus". The American Naturalist 12 (4): 235–238. doi:10.1086/272082. http://links.jstor.org/sici?sici=0003-0147%28187804%2912%3A4%3C235%3AAP%3E2.0.CO%3B2-7. Retrieved 2007-06-20. 








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