Fission or Division विखंडन, Asexual Reproduction by Fission or Division विखंडन द्वारा अलैंगिक प्रजनन
Channel: Biologyhub Prakashsir AP
Date: 2021-05-07

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Biologyhub Prakashsir Ap
Biology Hub Prakash Sir Ap
Prakash Kumar
Kumar Prakash
विखंडन द्वारा अलैंगिक प्रजनन
Asexual Reproduction by Fission Or  Division
Asexual reproduction
 
Fission or Division is the type of asexual reproduction in which any unicellular organism divide into two or more equal part. 
Types of Fission
[A]  Binary Fission
[B] Multiple Fission
[C] Plasmotomy
[A] Binary fission is the types of fission in which any unicellular organism body divide into two equal part.Depending on the plane of fission, binary fission is of the following types
i.               Simple irregular binary fission
ii.               Transverse binary fission
iii.               Longitudinal binary fission
iv.               Oblique binary fission
  Simple binary fission is seen in Amoeba like irregular shaped organisms where the plane of division is hard to observe. The contractile vacuoles cease to function and disappear. The nucleoli disintegrate and the nucleus divides mitotically. The cell then constricts in the middle, so the cytoplasm divides and forms two daughter cells.
In transverse binary fission, the plane of the division runs along the transverse axis of the individual. e.g. Paramecium and Planaria. In Paramecium the macronucleus divides by amitosis and the micronucleus divides by mitosis.
In longitudinal binary fission, the nucleus and the cytoplasm divides in the longitudinal axis of the organism In flagellates, the flagellum is retained usually by one daughter cell.

The basal granule is divided into two and the new basal granule forms a flagellum in the other daughter individual. e.g. Vorticella and Euglena.
In oblique binary fission the plane of division is oblique. It is seen in dinoflagellates. e.g. Ceratium

[B]In multiple fission the parent body divides into many similar daughter cells simultaneously. First, the nucleus divides repeatedly without the division of the cytoplasm, later the cytoplasm divides into as many parts as that of nuclei. Each cytoplasmic part encircles one daughter nucleus. This results in the formation of many smaller individuals from a single parent organism. If multiple fission produces four or many daughter individuals by equal cell division and the young ones do not separate until the process is complete, then this division is called repeated fission e.g. Vorticella.

[C]In Plasmodium, multiple fission occurs in the schizont and in the oocyte stages. When multiple fission occurs in the schizont, the process is called schizogony and the daughter individuals are called merozoites When multiple fission occurs in the oocyte, it is called sporogony and the daughter individuals are called sporozoites. 
During unfavorable conditions (increase or decrease in temperature, scarcity of food) Amoeba withdraws its pseudopodia and secretes a three-layered, protective, chitinous cyst wall around it and becomes inactive. This phenomenon is called encystment. When conditions become favourable, the encysted Amoeba divides by multiple fission and produces many minute amoebae called pseudopodiospore or amoebulae. The cyst wall absorbs water and breaks off liberating the young pseudopodiospores, each with a fine pseudopodia. They feed and grow rapidly to lead an independent life. 
In some metazoan animals, a special type of transverse fission called strobilation occurs. In the process of strobilation, several transverse fissions occur simultaneously giving rise to a number of individuals which often do not separate immediately from each other e.g. Aurelia.  
Plasmotomy is the division of multinucleated parent into many multinucleate daughter individuals with the division of nuclei. Nuclear division occurs later to maintain normal number of nuclei. Plasmotomy occurs in Opalina and Pelomyxa (Giant Amoeba).
During unfavourable conditions Amoeba multiplies by sporulation without encystment. Nucleus breaks into several small fragments or chromatin blocks. Each fragment develops a nuclear membrane, becomes surrounded by cytoplasm and develops a spore-case around it. When conditions become favourable, the parent body disintegrates and the spores are liberated, each hatching into a young amoeba.