We explain what amoebas are and some characteristics of this group of protists. Also, your observations and approximate size.
What is an amoeba?
Amoebas or amoebas are single-celled eukaryotic organisms that crawl by using pseudopodia (“false feet”). They make up one of the four groups of amoeboid protozoa (foraminifera, heliozoa and radiolarians) that belong to the Kingdom Protista.
The pseudopodia are mobile extensions of the cytoplasm of amoebas. They allow them to move across a surface and phagocytize (engulf) food. These extensions can be wide and pointless (lobopodia), thin, thread-like (filopodia) or reticular (rhizopodia).
Amoebas are also characterized by having a large cell nucleus and a contractile vacuole with which they regulate the amount of water inside the cell (and, therefore, the tonicity). However, many marine amoebas lack this vacuole and freshwater amoebas may have several.
These organisms lack a cell wall, but may have a shell or testa that surrounds them. Naked amoebas usually live in salt and fresh water and moist soil. On the other hand, shelled amoebas live mostly in fresh water, moist soils and mosses. Not all of them are free-living, since there are species that are parasitic. Some are even in the air.
Amoebas typically measure from a few micrometers (μm) to a millimeter. For example, some intestinal amoebas measure between 9 to 15 µm, while the largest species Polychaos dubium (parasitic to humans) can be seen with the naked eye because it reaches more than 1 mm in length.
Amoeba Nutrition
Amoebas are heterotrophic organisms. Those that inhabit land and water They feed on decaying matter or organisms smaller usually bacteria, algae or fungi.
To do this, they use pseudopodia, with which they encompass the food particle and incorporate it through their cell membrane. In the cytoplasm, food is digested within digestive vacuoles. This process is called phagocytosis.
Some species have developed a parasitic life and need to invade the internal systems of multicellular organisms to survive and reproduce. They generally parasitize the digestive tract of annelids, insects and vertebrates (including humans). For example, Entamoeba histolytica It is a human intestinal parasite that causes amoebiasis.
Generally, amoebas have aerobic respiration, that is, his metabolism It depends on the oxygen they take in from the atmosphere through its membrane. However, some have anaerobic respiration (such as E. histolytica). These amoebas that live in places without oxygen may lack mitochondria.
Reproduction of amoebas
Amoebas reproduce asexually, that is, they do not produce gametes nor do they need a reproductive partner to be able to leave offspring. Sexual reproduction has very rarely been observed in amoebas.
Generally, the reproduction mechanism is binary fission. In this process, The genetic material of the “mother” amoeba is duplicated by mitosis and the cytoplasm divides into two equal parts. In those amoebas that have a shell, it also divides into two.
Each half of the “mother” amoeba gives rise to a new individual that is identical to its parent because it receives a copy of its genetic material. Although this type of asexual reproduction is rapid (compared to sexual reproduction), it does not provide genetic variability to the offspring.
Classification of amoebas
Amoebas were first observed in 1757, by the German naturalist August Johann Rösel von Rosenhof. From his observations on the changing shape of the organism, the first observed species was named Amoeba proteus (an allusion to the Greek god Proteus, capable of changing shape at will).
They were formerly classified within the kingdom of animals, but later they were included in the kingdom of protists. At first they were classified together with other amoeboid protozoa (foraminifera, heliozoans and radiolarians) within the phylum Sarcodina or Rhizopoda, but this has since fallen into disuse.
Currently, most amoebas are grouped into one of the five supergroups of eukaryotic living beings, called Amoebozoa. However, some amoeboid organisms belong to other groups. This is because molecular phylogenetics changed the course of the taxonomic classification of eukaryotes.
Examples of amoebas
Some examples of amoebas are:
- Amoeba proteus. Large, free-living amoeba that lives in freshwater environments. It is the best known amoeboid species.
- Arcella vulgaris. Amoeba with a testa that lives in freshwater environments.
- Difflugia sp. Amoeba with testa formed from sand particles, living mainly in swamps.
- Entamoeba histolytica. Parasitic amoeba of the human and canid intestine, causing dysentery.
- Acanthamoeba sp. Free-living amoeba found in air, water and land. They can infect the cornea of humans.
- Naegleria fowleri. Temperate freshwater amoeba (hot springs, pools, rivers), which causes brain infections in humans.
See also: Viruses in biology
References
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- Ruppert, E.E., & Barnes, R.D. (1996). Invertebrate zoology. (6th ed.). McGraw-Hill Interamericana.
- Rushforth, SR, Robbins, RR, Crawley, JL, & Van de Graaff, KM (2008). A photographic atlas for the botany laboratory. (5th ed.) Morton Publishing Company.
- Vidyasagar, A. & Dutfield, S. (February 26, 2022). What is an amoeba? Live Science.
- Anderson, O.R. (2011) Rhizopoda. Encyclopedia of Life Sciences. Doi.org
- Treviño Rodríguez, JG (sf). Etymology of amoeba. Online Spanish Etymological Dictionary. Etymologies
- Pereira, Á and Pérez Ríos, M. (2003). Free-living amoebas. Offarm: pharmacy and society22(6), 114-117. Elsevier.es
- Sard, BG, Navarro, RT and Sanchis, JGE (2011). Non-pathogenic intestinal amoebas: a clinical-analytical view. Infectious Diseases and Clinical Microbiology29(3), 20-28. Doi.org
