There are two types of reproduction–
In asexual reproduction sex organs don’t take part.
Hence, single organisms usually reproduce by asexual methods.
For sexual reproduction activities of both the male and the female sex organs together is essential.
Hence, two organisms- male and female are essential for sexual reproduction. Now let us study some basic methods of reproduction in single organisms.
Fission or Binary Fission
When a cell gets fully matured, its nucleus divides into two.
Each one of the two nuclei takes its half share of cytoplasm, forms a membrane around and gets separated as a new cell.
Each new cell is called as a daughter cell. This method of asexual reproduction is called as fission or binary fission. In Baker’s yeast and amoeba asexual reproduction takes place by this method.
The malaria parasite (Plasmodium sp.) covers itself with a cyst in adverse conditions.
The cyst breaks when favourable conditions occur.
Before the breaking out of the cyst the nucleus of the cell divides many times to form innumerable nuclei. Each new nucleus takes its share of cell material and becomes round ready to perform like a new cell.
When cyst breaks numerous new cells with proper nuclei come out and develop to form a number of organisms. This method of asexual reproduction in a single organism is called multiple fission.
Usually filaments of spirogyra- an alga get broken by mechanical reasons. Afterwards each of the broken pieces develops into a new spirogyra. This process is called as Fragmentation.
The word ‘regeneration’ is made up of two parts re- and –generation which means ‘originate again’. If any part of the body of an organism (say tail of a lizard) is cut in an accident, it develops again to its full length within a time period. This process is called as regeneration. Body construction, repair and development continue in organisms but these are not similar in all the organisms. Some examples –
- Replacement of dead and injured cells into new ones
- Healing of wounds
- Development of new organs
- Development of a new organism from any part of the body
Above mentioned developments occur in many different organisms and are examples of regeneration. Asexual processes of repair of injured or useless organs of a body, origin of a new organ from any part of the body of an organism that occurs automatically in the body of an adult organism is called as regeneration.
In this method of asexual reproduction a bulb like growth starts somewhere on the outer layer of the body. The nucleus of the cell producing bulb divides in two parts and one part is retained inside the bulb. This bulb like bud may produce other bulbs or may get detached and fall down. The development of this bud into an individual is called as budding. Example: Yeast cell and the multicellular organism Hydra reproduce asexually through this method.
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