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Editor-In-Chief: C. Michael Gibson, M. 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. Amoeba itself is found in decaying vegetation in fresh and salt water, wet soil, and animals. Due to the ease with which they may be obtained and kept alive they are common objects of study, both as representative protozoa and to demonstrate cell structure and function.
The cells have several lobose pseudopods , with one large tubular pseudopod at the anterior and several secondary ones branching to the sides. Its most recognizable features include a single nucleus and simple contractile vacuole to maintain osmotic pressure. The amoeba obtains its food through phagocytosis. Amoebas reproduce through binary fission. 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 Bery St. An amoeba, from the order Amoebida, class Mastigophora phylum sarcodina protozoa, [2] is a single-celled organism. They live in freshwater stagnant ponds, soil, streams, the ocean, and the bodies of other organisms. Some of the largest amoebae are about 1mm across, which means a human being would barely be able to see it with the naked eye. Species that possess a CV always use it, even in very hypertonic high concentration of solutes environments, since the cell tends to adjust its cytoplasm to become even more hyperosmotic hypertonic than the environment.
The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment. In hyperosmotic environments, less water will be expelled and the contraction cycle will be longer. The number of CVs per cell varies, depending on the species.
Amoeba have one; Dictyostelium discoideum , Paramecium aurelia, and Chlamydomonas reinhardtii have two; and giant amoeba, such as Chaos carolinensis , have many.
In some unicellular eukaryotic organisms e. In Paramecium , which, presumably, has the most-complex and highly-evolved CV, the vacuole is surrounded by several canals, which absorb water by osmosis from the cytoplasm.
After the canals fill with water, it is pumped into the vacuole. When the vacuole is full, it expels the water through a pore in the cytoplasm that can be opened and closed. Amoebae survive in hypotonic environments because they have contractile vacuoles to pump excess water out of the cell. To regulate osmotic pressure, most freshwater amoebae have a contractile vacuole CV that expels excess water from the cell.
This organelle is necessary because the surrounding water is hypotonic with respect to the contents of the cell. Water is transferred across the amoeba's cell membrane by osmosis. I couldn't find a good video on amoebae, but here is a good video showing the operation of CVs in paramecia. How can an amoeba survive in hypotonic environment? Ernest Z. Jun 27,
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