what is asexual reproduction ? explain the different methods of asexual reproduction with examples ?
Answers
Modes of Asexual Reproduction. Organisms choose to reproduce asexually by different means. Some of the asexual methods are binary fission (e.g. Amoeba, bacteria), budding (e.g. Hydra), fragmentation (e.g. Planaria), spore formation (e.g. ferns) and vegetative propagation (e.g. Onion).
ANSWER :
ASEXUAL REPRODUCTION :
- When a single parent is involved in the formation of new individual, without the fusion of gametes, it is called asexual reproduction.
- It involves repeated mitotic divisions.
- No gametes are formed during asexual reproduction.
- No or little variations occur during asexual reproduction.
DIFFERENT METHODS OF ASEXUAL REPRODUCTION WITH EXAMPLES ARE :
- The various methods of asexual reproduction are fission ( binary and multiple ) , fragmentation , regeneration , budding, vegetative propagation, and spore formation.
i) Fission :
a) BINARY FISSION : When a single unicellular organism, splits to form two new individuals, first by nuclear division and then by cytoplasmic division, it is called binary fission.
The splitting of the cells can take place in any plane. It occurs during favourable conditions in unicellular organisms such as Amoeba, Paramecium , Euglena, etc.
In Leishmania, binary fission occurs in definite orientation in relation to body structure.
b) MULTIPLE FISSION : Multiple fission involves division of a single unicellular parent into a number of daughter organisms. The nucleus divides repeatedly, each daughter nucleus moves to the periphery, get covered with cytoplasm to form many daughter individuals. It is a common mode of reproduction in Plasmodium when it invades the RBC of man. It occurs during unfavourable conditions.
ii) Budding :
a) IN HYDRA : A bulge or projection appears as a result of repeated mitotic division on the lateral side of the parent's body. It grows on the parent body to resemble a small Hydra. When the new Hydra matures, a constriction at its base separates it from its parent.
b) IN YEAST : A bud starts as a small outgrowth from the surface of the adult cell. As it enlarges, the nucleus of the adult cell divides and then the bud get pinched off but still remains attached to the parent cell. This is turn produces another bud at its tip and the process continues 3 - 4 times in chain of yeast cells.
iii) Spore Formation :
It mostly occurs in fungi and bacteria. The spores develop on a structure called sporangium found on slender, erect fungal hyphae. Within the sporangium, a nucleus divides several times and each daughter nucleus gets surrounded by a bit of cytoplasm to form a spore. A spore is small microscopic structure with a thick wall. It is light and air borne. The sporangium on maturing bursts to release the spores, which in favourable conditions germinates into an entirely new organism eg : Rhizopus , Mucor , Penicillium etc.
iv) Regeneration :
It is the ability of a fully differentiated organism to regenerate the whole body from their body parts.
In Planaria and Hydra, if the individual is cut or broken into many parts, a small piece is capable of regeneration of the entire individual.
Regeneration is carried out by specialized cells.
v) Fragmentation :
Fragmentation is the method of breaking up of an organism into smaller pieces or fragments which grow into new organisms as in algae Spirogyra.
In simple, multicellular organisms like Spirogyra the body / fragment breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.
vi) Vegetative Propagation :
The process by which some plants can reproduce asexually by their vegetative parts like roots , stem and leaves is called vegetative propagation.
Example : vegetative propagation by leaves in bryophyllum