Did You Know?
Some hundred years ago, naturalists referred to amoeba as Proteus animalcule, after Greek God Proteus, who had the ability to alter his shape.
Amoebae (plural of amoeba
) are large protozoans and single-celled organisms belonging to the genus Protozoa and phylum Sarcodina. They are shapeless (their shape keeps changing), and the largest of these organisms may grow to a size of 1 mm. Amoebae mostly thrive in moist environmental conditions, such as soil, bottom of freshwater ponds, puddles, streams, and seawater, or as parasites in animals, including humans. They move around with the help of their false feet called pseudopodia, which are small projections of the cell. These pseudopodia play a vital role in the metabolic activities, like locomotion, eating, etc., of an amoeboid.Stages in the Life Cycle of an Amoeba
An amoeba reproduces asexually by a process called binary fission.Metabolic Activities in Amoeba
» It starts by pulling in the pseudopodia to attain a spherical shape.
» Mitotic cell division takes place, which constricts the nucleus and cytoplasm to form two daughter cells.
» Thus, the genetic information in the nucleus is copied in both the cells which makes them identical. The nucleus is the most vital part of an amoeba and is the key to its survival. The free amoebae are called trophozoites. Binary fission in amoebae may last for anywhere around 30 - 60 minutes under ideal conditions.
Amoeba can also reproduce by a process called multiple fission. It usually applies this process under abnormal circumstances, wherein the environment lacks the necessary nutrients. The process begins in the same way as binary fission.
» Amoeba retracts its pseudopodia and attains a more spherical shape.
» In hostile or dangerous situations, where natural conditions make survival difficult for the amoeba, it forms a protective covering, like a wall around itself to form a cyst. This cyst is able to survive harsh and rough conditions which are potentially harmful for a normal amoeba.
» Inside the cyst, multiple mitosis takes place. This process produces many daughter cells inside the cyst, which are protected against the unsuitable environment.
» Once favorable conditions prevail, the cyst ruptures and daughter amoebae are released from it. These cysts are responsible for causing infection and contaminating food and water.
The amoeba that is armored in protective covering around itself is often termed as 'microbial cyst.' If the amoeba stays in the microbial cyst stage for a long time, it may die due to lack of food and will also be incapable of reproducing.
The amoeba is made up of same parts or organelles, like that of a normal cell. Being a single cell, it is enclosed in a cell membrane. It contains a nucleus (brain-like organ of amoeba that controls its actions), organelles (organs of amoeba) and cytoplasm (fluid within the cell membrane). A method known as phagocytosis is used by amoeba for locomotion, feeding, and reproduction. During phagocytosis, amoeba changes its shape and reassembles itself. During feeding, the amoeba engulfs food and then disintegrates it within the cell membrane. Once the food has been enveloped, organelles known as food vacuoles, do the task of digesting it and storing it.
The useful nutrients are absorbed, while anything that's potentially harmful remains in the food vacuole, from where it is eventually pushed to the surface via the cell membrane―this process is called egestion.
There are many amoeboids that affect human beings and cause various diseases. Some of these are given below:
» Entamoeba histolytica causes amoebic dysentery or amoebiasis.
» Naegleria fowleri is a freshwater-dwelling species that can attack the brain and nervous system in humans.
» Acanthamoeba can affect the eyes or brain of humans, causing keratitis or encephalitis, respectively.
Amoebae are very important life forms, as they are the basis on which many other life forms have evolved. Without amoeba, evolution of other organisms would not be possible. Although there exist many different amoeba with varying life cycles, majority are replicas of their parent. Once they attain maturity, they divide by mitosis, and the initiate the process of dividing, feeding, and maturing all over again.