Classification of Amoeba (Ameba)

Amoeba is a simple, single-celled eukaryotic organism that lacks a definite shape. To know more about the characteristics and classification of Amoeba, read on…

Amoeba, also referred to as Ameba, is a genus that belongs to protozoa, which are unicellular eukaryotes (organisms with membrane-bound cell organelles). The name Amoeba is derived from the Greek word amoibe, which means change. There are many species of Amoeba, of which the most extensively studied is A. proteus (Amoeba proteus). Majority of the Amoeba species are very minute and are not visible to the naked eye. However, in spite of its small size, the genomic content of Amoeba is several times more than the human genome. The species A. dubia consists of about 370 billion base pairs; whereas, human genome has about 3 billion base pairs.

Amoeba (plural Amoebae or Amoebas) is found in terrestrial as well as aquatic habitats. Some are parasitic in nature, which are responsible for causing ailments in humans and animals. There are six parasitic species of Amoeba that may result in certain diseases in humans. Let’s discuss in brief about the characteristics and classification of Amoeba.

Amoeba (Ameba): Characteristics The cytoplasm and cell organelles of Amoeba are enclosed by a cell membrane. Since there is no cell wall, the cellular structure of Amoeba is not definite. It can exhibit any form, based on the surrounding condition. An Amoeba can have more than two nuclei in the cell. It possesses pseudopodia for locomotion and feeding purposes. The pseudopods are extensions of the cytoplasm. Amoeba engulfs food by means of phagocytosis; it encircles bacteria

or other smaller protists, and secretes digestive enzymes into the vacuoles. Digestion of food particles takes place in the vacuole with the help of enzymatic actions.

Similar to other protozoans, Amoeba reproduces asexually either by mitosis or cytokinesis. Under forceful division of Amoeba, the portion that contains nucleus survives, while the portions without nucleus die. When Amoeba is exposed to lethal environments, it turns into a dormant form, known as Amoebic cyst. It continues to remain in the cyst form until it encounters normal environmental conditions.

Amoeba is extremely sensitive to stimuli, which is evident from shrinkage or expansion of cell, depending on the surrounding condition. The vacuoles are responsible for maintaining the osmotic pressure inside the cell. When Amoeba is kept in a hypertonic saline solution (concentrated), the cell shrinks and prevents entry of salt. On the contrary, when it is exposed to hypotonic freshwater, Amoeba cell expands and swells.

Amoeba (Ameba): Classification

As Amoeba lacks characteristic morphological features, its classification is often vague and confusing. It is also partly due to the fact that many other species of protists resemble Amoeba in their anatomy and behavior. One of the characteristic features that distinguishes marine Amoeba from freshwater Amoeba is the lack of contractile vacuoles and their enzymes.

Kingdom:

Protist

Phylum:

Protozoa

Class:

Sarcodina

Sub-Class:

Rhizopoda

Order:

Amoebida

Family:

Amoebidae

Genus:

Amoeba Species: proteus, animalcule, dubia, animalcule

, etc.

Scientific studies are ongoing to classify Amoeba by using small subunit ribosomal RNA (SSU rRNA) genes. Amoeba is extensively studied in cell research in order to determine the relation between the cytoplasm and the nucleus of the cell. As Amoeba is one of the simplest forms of eukaryotic organisms on Earth, it is often studied as a representative organism in the process of evolution.