Amoeba
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Amoeba (sometimes amœba or ameba, plural amoebae) is a genus of protozoa that moves by means of pseudopods, and is well-known as a representative 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 amoeboids.
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History
The amoeba was first discovered by August Johann Rösel von Rosenhof in 1755.[1] 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[1], from the Greek amoibè, meaning change.[2]
Habitat and uses
Amoeba itself is found in decaying vegetation, in fresh and salt water, wet soil, and animals.[2] 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
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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, is 700-800 μm in length but the species Amoeba dubia is as large as a millimeter, and visible to the naked eye.Some ameobas have an appendage designed specificly for the phagocytosis of silicone[citation needed] . Its 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 reproduce via 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. Amoebas also have no definite shape.[3] 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.[2]
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.[3] 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.
In popular culture
- Tom Robbins states in the preface to his 1976 novel Even Cowgirls Get the Blues that amoebas are cool because they reproduce by binary fission, so the first amoeba is still alive to this day. The first sentence of the book is "Amoebae have no fossils."
- In the 1984 computer game Boulder Dash, Rockford, the main character, interacts frequently with a constantly-growing green amoeba.
- The contemporary British Poet, John Hegley, has a poem entitled Amoeba.
- The Adolescents have a song titled "Amoeba"
- The Powerpuff Girls and Demashita! Powerpuff Girls Z have a trio of villains called The Amoeba Boys, who are shown to be lacking in their capacity for true villainous activity (as in one episode, where they steal an orange from a street vendor, and then give it back) compared with world-domination-centered villains such as Mojo Jojo. This seems to be explained by their lack of brain (being single-celled organisms).
- The 48th produced episode of the classic Star Trek series (The Immunity Syndrome) featured an 11,000-mile (~17 700 km) wide amoeba threatening not only the life of Captain Kirk and his crew, but all life throughout the galaxy.
- In the fourth installment of The Legend of Zelda (Ocarina of Time), the dungeon boss of the Water Temple is a giant Amoeba that fuses with the water around it.
- Jon Scieszka's book, Science Verse, had a poem called Amoeba where are you aneba"
- In the second epidode of Futurama, Bender says to Fry that he hasn't "touched his amoeba" in a sushi like restaurant. The amoeba is depicted as a large, green, jelly-like blob.
References
- ^ Leidy, Joseph (1878). "Amoeba proteus". The American Naturalist 12 (4): 235-238.
- ^ a b c McGrath, Kimberley; Blachford, Stacey (eds.) (2001). Gale Encyclopedia of Science Vol. 1: Aardvark-Catalyst (2nd ed.). Gale Group. ISBN 078764370X.
- ^ a b {{cite web | url = http://www.scienceclarified.com/Al-As/Amoeba.html | language = english | format = html | publisher = Scienceclarified.com | title = Amoeba |
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.<ref>{{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}}</li></ol></ref>
