Types of asexual reproduction
1. Binary fission
One individual breaks into two. It is mitotic(in eukaryotes) or amitotic (in prokaryotes) process.
Types of binary fission
Fission can take place from any arbitrary plane of body
Fission takes place through the longitudinal plane
Eg. Euglena, trypanosome, giardia, lesihmania
Fission takes place along the transverse plane
Eg. Paramecium (the part without cytostome i.e the upper part is caller proter and the part with cytostome i.e the lower part is called opisthe )
Mostly in dinoflagellates, ceratium
In organisms which undergo binary fission, there is no concept of senescene or natural death
It is mode of reproduction in favourable conditions.
Quesn : What will happen if paramecium is kept constantlyin favourable condition? (assume that only binary fission takes place and sexual reproduction doesn’t take place)
Ans. Paramecium population will die as the surface area volume ratio increases rapidly with each division. So, metabolic rate increases rapidly that results in their death.
That is why they involve in sex. Reproduction by conjugation.
2. Multiple fission
It takes place during unfavourable conditions. Usually, Cyst is formed and many nuclei are produced
Eg. In amoeba ,sometimes, nucleus divides repetitively but no cyst is formed. It is called psuedopodiospores.
If cyst also develops in the amoebulae thus formed, it is called encysted spore or encysted amoebulae.
Multiple fission is of two types.
In protozoans, a trophozoite increases in cell size and its nucleus divides repeatedly along with some organelles. The organism in such condition is called as schizont. The schizont eventually ruptures, releasing merozoites
Sporulation involving multiple fission of sporonts, resulting in formation of sporocysts or sporozoites. It can also be seen as reproduction by asexual division of spore or zygote.
(plasmo = cytoplasm , tomy = cut)
Only cytokinesis but not karyokinesis takes place. It is a modified multiple fission
As u may have guessed, it can be seen only in multinucleated organism.
Eg. Opalina ( it occurs in seminal vesicles of earthworm)
Eg2. pelomyxa (also called as giant amoebulae)
After plasmotomy, some cells may get uninucleated, but with time, karykinesis occurs (for development)
This can be seen only in organisms with low organization level.
Eg.. sponges, coelentereates upto echinoderms.
It is of two types
Eg. Gemmules formation (mesoglear) in sponges. It is protected by spicules
Eg. Hydra, sponges, tunicates etc.
In hydra budding takes place towards proximal end.