Amoeba
Definition
Amoebas, amoebae, or amoeboids is a generalised terminology that refers to a particular type of motile organism. Amoebas are eukaryotic cells or organisms composed of a single cell that modify their shape as a means of motile action. These types of organisms are found in protozoa, fungi and animal lineages.[1] Amoebas are found in abundant numbers across the planet, either in a hard outer shell, known as “testate” or “naked” without one. [2]
Movement
The many different types of amoeba move through the use of a structure known as a pseudopod, which means “false foot.” These are bends of the plasma membrane which allow the cytoplasm of a cell to spill into a particular direction, and then serve as an anchor to pull the rest of the cell in the desired direction. The action of the plasma membrane is controlled by actin filaments, similar to how our muscles flex. [3] These pseudopods can take on a myriad of forms, ranging from branching filamented protrusions, bloblike lobes or thin tapering points. [4]
Anatomy
Amoebas, across their multitude of taxonomic distributions, vary greatly in their anatomical morphologies. Different species of amoebas that live in different environments have pressures to survive that require unique solutions. Some amoeba, known as testate amoeba have a hard outer shell with which they protect themselves from harm. These shells vary greatly based on species, and can be made of a multitude of substances containing silica, calcium, chitin, sand grains and diatoms. [2] The osmotic potential of water in an amoeba is subject to high variability in freshwater systems, and as such amoeba in this environment require the use of a contractile vacuole. This organelle can absorb or release water as needed to maintain stable conditions. [3]
Dietary Processes
The major action by which amoebas consume matter is through a process known as phagocytosis. When an amoeba encounters a particle of food, it responds by surrounding the particle with its various pseudopods, creating a vacuole of the food within its cytoplasm, and digests it with enzymes before releasing the processed material into its environment. Amoebas consume a variety of things, ranging from algae, bacteria, other protozoa to dead or decaying matter.[4] Protozoan amoebas are responsible for the consumption of massive amounts of bacteria. The growth of these protozoan amoebas in response to bacterial growth is thought to assist in the nutrient cycling and brings nutrients such as nitrogen from decaying matter closer to the root systems of plants. [5]
References
[1] "The Amoebae". The University of Edinburgh. Archived from the original https://web.archive.org/web/20090610035748/http://www.bms.ed.ac.uk/research/others/smaciver/amoebae.htm
[2]Ogden, C. G. (1980). An Atlas of Freshwater Testate Amoeba. Oxford, London, and Glasgow: Oxford University Press, for British Museum (Natural History). pp. 1–5. ISBN 978-0198585022.
[3]Alberts Eds.; et al. (2007). Molecular Biology of the Cell 5th Edition. New York: Garland Science. ISBN 9780815341055.
[4]David J. Patterson. "Amoebae: Protists Which Move and Feed Using Pseudopodia". Tree of Life web project. http://tolweb.org/accessory/Amoebae?acc_id=51
[5]Clarholm, M. (1981). Protozoan grazing of bacteria in soil—impact and importance. Microbial Ecology,7(4), 343-350. doi:10.1007/bf02341429 https://link.springer.com/article/10.1007/BF02341429
[6]Thorp, James H. (2001). Ecology and Classification of North American Freshwater Invertebrates. San Diego: Academic. p. 71. ISBN 0-12-690647-5.