Methods of asexual reproduction

December 3, 2018

It is a common method of reproduction in lower plants and animals.
A single organism is involved in this method i.e. capable of reproduction.
The method of reproduction where a single parent is involved and there is no fusion of male and female gamete is asexual reproduction.
Sex cells or gametes are not involved.
The new offspring produced are genetically identical to their parents.
The various methods are:

a) Fission

b) Budding

c) Sporulation

d) Fragmentation or regeneration

e) Vegetative reproduction

A) Fission

In this method, a parent organism divides or splits into two or more daughter organisms.
It is common in unicellular organisms like amoeba, paramecium, plasmodium, bacteria, euglena, etc.
It is of two types depending on the number of daughter organisms produced.

i) Binary fission

A single parent divides into two daughter organisms in this method.
The nucleus divides first into two daughter nuclei which is followed by the division of cytoplasm.
The cell splits into two daughter cells finally.
This results in the formation of two daughter organisms.
The parent organisms cease to exist and the daughter one comes to existence.
It occurs during favourable condition of life.
The off-springs obtained are morphologically and genetically identical to parent.
E.g. bacteria, euglena, amoeba, paramecium, plasmodium, etc.

Image source: snapsolve

ii) Multiple fission

A single parent divides or splits into more than two daughter organisms at the same time.
It occurs generally during unfavourable conditions.
Many unicellular algae and some unicellular animals like amoeba, plasmodium, etc. follow this method of reproduction.
A cyst is formed initially which is a thick protective layer around the cell under unfavourable conditions.
The nucleus first divides repeatedly to form many daughter nuclei.
Later on, each nucleus gets surrounded by the cytoplasm and cell membrane.
Many daughter cells are formed inside the cyst finally.
Under favourable conditions, the cyst breaks and small offspring are released.

Image source: toppr

B)Budding

A bulb-like projection i.e bud arises from the parent’s body in this method.
This bud detaches from the parents body and finally develops into new organism.
Thus, the method of asexual reproduction which takes place by the formation of a bud is called budding.
Unicellular plants like yeast and multicellular organism like hydra follow this method.

C) Sporulation

This method is common in the majority of thallophytes and bryophytes.
The parent plant produces a large number of tiny spores which can produce new plants.
This method is common in mucor, moss, fern, Marchantia, Rhizopus, Chlamydomonas, etc.
Thus, the method of reproduction which takes place by means of spores is called sporulation.
A small-knob like structures called sporangia (singular- sporangium) develops at the top of the hyphae.
Numerous spores are produced inside the sporangium.
Spores are the microscopic asexually reproductive bodies covered by a hard protective coat.
At maturity, the sporangium bursts and spores are released.
Under favourable condition, the spores germinate into new organisms.

D) Fragmentation and Regeneration

The multicellular organism breaks into two or more fragments and each fragment develops into a new complete organism. It is called fragmentation.
The ability of an individual fragment of an organism to replace its lost parts is called regeneration.
It can also be defined as the process of getting back a complete organism from its body parts.
Filamentous algae like Spirogyra and animals like Hydra, Planaria, Tapeworm, Sponge, etc. reproduce by this method.
Fragmentation is generally used for plants while regeneration is common for animals.

E) Vegetative propagation

This is common in some higher plants.
A bud grows on the vegetative parts of a plant like the stem, root or leaf and develops into new plant.
On maturity, the new plant detaches itself from the parent plant and lives as an independent plant.
The method of asexual reproduction in which new plants are produced by cutting, sowing or grafting of the vegetative parts of plants like stem, root or leaf is called vegetative propagation.