Amoeba characteristics, taxonomy, morphology, nutrition

Abraham McLaughlin

Amoeba is a genus of unicellular organisms of the Kingdom Protista. They are openly known as protozoa and are generally microscopic in size. Individuals of this genus are the simplest eukaryotes from a functional and structural point of view. Because of this, their processes are also very basic.

It was discovered in 1757 by Johann Rösel Von Rosenhof, a botanist of German origin. The best known and most representative species of this genus is the Amoeba proteus, which is characterized by the extensions that come out of its body, known as peudopods and that serve to move and feed.

Examples of Amoebas. Source: By Picturepest (original picture), Nina-marta (modification) [CC BY 2.0 (], via Wikimedia Commons

Most amoebas are harmless to humans. However, there are some species that can wreak havoc on health, being able to give rise to pathologies that, if not treated, can degenerate into fatal outcomes. Among these, the best known infection is amebiasis, which causes diarrhea, abdominal pain and general malaise..

Article index

  • 1 Taxonomy
  • 2 Morphology
    • 2.1 Shape
    • 2.2 Vacuole
    • 2.3 Cytoplasm
  • 3 General characteristics
  • 4 Habitat
  • 5 Nutrition
    • 5.1 Ingestion
    • 5.2 Digestion
    • 5.3 Absorption
    • 5.4 Assimilation
    • 5.5 Excretion of waste substances
  • 6 Breathing
  • 7 Playback
  • 8 References


The taxonomic classification of the genus Ameba is as follows:

Domain: Eukarya

Kingdom: Protista

Edge: Amoebozoa

Class: Tubulínea

Order: Euamoebida

Family: Amoebidae

Gender: Amoeba


Organisms of the genus Amoeba They are unicellular, which means that they are made up of a eukaryotic cell.

They have the typical structure of a eukaryotic cell: cell membrane, cytoplasm with organelles and cell nucleus. They do not have a defined shape, since their membrane is quite flexible and allows it to adopt various shapes.

Through the cell membrane they manage to establish communication with the external environment, through the exchange of substances, either for food or for other processes such as respiration..

Regarding the size, there are several. For example, the best known species of this genus, the Amoeba proteus it measures approximately 700 - 800 microns in length. However, there are much smaller species.


Like many other protozoa, members of this genus can present two forms:

  • Trophozoite: It is the so-called activated vegetative form. When the organism is in this state it can feed and reproduce. Among its most outstanding characteristics is that it has a single nucleus and presents a structure known as a karyosome. This is nothing more than chromatin condensed around the nucleus.
  • Cyst: it is a highly resistant form to harsh environmental conditions. It is the way in which you can infect a new host.


One of the most recognizable elements within the morphology of the amoeba is the vacuole. A vacuole is a sac-shaped cytoplasmic organelle that is bounded by a membrane.

There are several types: storage, digestive and contractile. In the case of amoebae, they have a contractile vacuole, which allows them to remove excess water from the cell interior.


The cytoplasm of the amoeba has two clearly distinguishable areas: an internal one, called endoplasm, and an external one known as ectoplasm..

The body of the amoeba gives off some extensions that are called pseudopods.

Paradoxically, despite being one of the simplest living organisms, it has one of the largest genomes, even having 200 times more DNA than human beings.

General characteristics

Organisms belonging to the genus Ameba are eukaryotes. This implies that their cells have a cell nucleus, delimited by a membrane. Within it is contained the genetic material in the form of DNA and RNA.

Similarly, they present a locomotion system through pseudopods. These are extensions of its cytoplasm, through which the amoeba anchors itself to a surface, to later propel itself forward..

In terms of their lifestyle, some of the known species of Amoeba are parasites of humans. They have a special predilection for the intestine, which they parasitize causing diseases such as amebiasis.


Living beings of the genus amoeba inhabit a great multitude of environments. They have been found in decaying vegetation, although they are particularly abundant in aquatic environments, either flowing or stagnant water..

Organisms of this genus can be found in sewage, stagnant water, and even bottled water. Likewise, they can be found in shallow pools and at the bottom of ponds or in the same mud..


Amoebas are organisms that, due to their type of diet, are considered heterotrophs. These types of individuals are not capable of making their own nutrients, as if plants do through the process of photosynthesis..

The nutrition of amoebae occurs through phagocytosis. By this is understood that process in which the cells ingest the nutrients to digest and metabolize them with the help of various digestive enzymes and the organelles found in their cytoplasm..

Digestion in amoebae encompasses several stages:


It is the process by which food enters the body that will take advantage of its nutrients. In the case of amoebas, for the ingestion process, they use pseudopods.

When perceiving some food particle nearby, the amoeba projects the pseudopods until it completely surrounds it. Once this has happened, the food is enclosed in a kind of bag known as a food vacuole..


This is a process that involves the fragmentation of nutrients into much smaller molecules that are easily usable by the body..

In amoebae, the nutrients that are contained within the food vacuole are subjected to the action of various digestive enzymes, which break them down and turn them into simpler molecules.


This process occurs immediately after the digestive enzymes have processed the ingested nutrients. Here, through simple diffusion, the usable nutrients are absorbed into the cytoplasm..

It is important to mention that, as in any digestive process, there are always undigested particles. These will remain in the food vacuole to be disposed of later..


During this stage, through different cellular mechanisms, the nutrients that were absorbed are used to obtain energy. This step is very important, because the energy that is generated is used by the cell for other equally important processes, such as reproduction..

Excretion of waste substances

In this phase, the undigested substances are released outside the amoeba. In this process, the vacuole in which the undigested particles were deposited fuses with the cell membrane in order to release them into the extracellular space..


Because the ameba It is one of the simplest living beings known, it does not have specialized organs to carry out the breathing process. This is unlike mammals that have lungs, or fish that have gills..

Taking the above into account, respiration in amoebas is based on a process known as diffusion. Diffusion is a passive transport (it does not imply energy expenditure) in which a substance crosses the cell membrane from a place where there is a high concentration of it to another where it is little concentrated.

In respiration in amoebae, oxygen (Otwo) diffuses into the cell. Once there, it is used in various metabolic processes, at the end of which carbon dioxide (COtwo). This gas (COtwo) is harmful to the cell, so it is expelled out of it, once again, through diffusion.


The type of reproduction of these organisms is asexual. In it, from an individual two exactly equal to the parent originate.

Amoebas reproduce through an asexual process known as binary fission, which is based on mitosis.

During this process, the first thing that happens is a duplication of DNA. Once the genetic material is duplicated, the cell begins to lengthen. Genetic material is located at both ends of the cell.

Prokaryotic fission, binary fission, is a form of asexual reproduction.

Subsequently, the cell begins to strangle, until the cytoplasm is completely divided, giving rise to two cells with the same genetic information as the cell that gave rise to them..

This type of reproduction has a certain disadvantage, since the living beings that originate through it will always be exactly the same as the parent. In this reproduction the genetic variability is totally null.

There is another variation in the reproductive process of the amoeba. Because living beings are not always in ideal environmental conditions, they have found it necessary to develop certain mechanisms that guarantee their survival..

Organisms of the genus amoeba are no exception. When faced with hostile environmental conditions, the cell develops a kind of very hard protective covering that completely covers it, thus constituting a cyst..

However, within the cyst the cellular activity does not cease, on the contrary. Protected from the damaging external environment, a large number of mitotic divisions take place within the cyst. This is how many cells are generated that will eventually transform into adult amoebae.

Once the environmental conditions are again favorable for the development and growth of amoebae, the cyst ruptures and all the daughter cells that had formed inside are released into the environment to begin their maturation process..


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  4. Kwang, J. (1973). The Biology of Amoeba. Academic press. 99-123
  5. Mast, S. (1926). Structure, movement, locomotion and stimulation in Amoeba. Journal of Morphology. 41 (2). 347-425

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