Asexual Reproduction

Reproduction in plants of Class 7

The process of producing new organism from a single parent without the involvement of sex cells or gametes.

Asexual reproduction takes place in unicellular organisms, some plants and some multicellular animals like sponges and Hydra.

Only one parent is involved; two sexes are not required.
Only mitosis takes place; meiosis never takes place.
New individuals (offsprings) are genetically identical to the parents, since they arise from only one parent; thus, no variations are introduced in the new organims.

Asexual reproduction produces identical organisms generation after generation. New organisms, therefore, inherit any defects of their parent.
Evolutionary change is not possible as no variations are produced. A species consequently cannot adapt to changes in its environment.

Vegetative propagation: This is a type of reproduction found in higher plants in which a new plant is formed from a vegetative part of the plant such as roots, stems ore leaves

(a) Cutting: This is the very common method of vegetative propagation practised by the gardeners all over the world. It is the process in which a vegetative portion from plant is taken and is rooted in the soil to form a new plant. e.g. Grapes, Sugarcane etc.
(b) Layering: In this process the development of adventitious roots is induced on a stem before it gets detached from parent plant, e.g., Mango, roses etc

Mound layering: In the process of layering the lower stem branch of plant is used. Leaves are removed from this stem. Then it is bent close to the ground, pegged and covered with the moist soil in such a way that it's growing tip remains above the soil surface. This pegged down branch is called as layer. After a few days the covered portion of stem develops roots. This stem is then detached from the parent plant and is grown separately into a new individual. e.g. Jasmine
Air layering: It is adopted in those plants where stem cannot be bent to the ground. In this process the stem is girdled (i.e. ring of the bark is removed). Then it is covered with moist moss or cotton and wrapped with a polythene sheet to preserve the moisture. After few weeks adventitious roots develop from the injured part. The branch along with roots is then separated from the parent plant and planted to grow into a new plant. e.g. Orange, Pomegranate etc.
Grafting: The process of joining together of two different plants in such a manner that they live as one plants is called as grafting. Out of the two plants one is rooted in the soil and is known as the stock. The other part consists of a small shoot bearing one or more buds it is known as scion. Their union is carried out in such a way that their cambium must overlap each other. e.g. Mango, roses etc

Formation of a daughter individual from a small projection which is called as bud, arising on the parent body is called as budding.

(A) Exogenous budding: [External budding] In this, bud arises from the surface of parent body.e.g., Hydra.
(B) Endogenous budding: [Internal budding] In this, bud arises inside or within the parent body. e.g., Sponges.

Fragmentation is the process in which the body of an individual breaks up into two or more parts and each part develops into a complete organism.
In some filamentous organisms such as the green alga Spirogyra, the filament break up into two or more fragments. Each fragment or piece grows into a new individual.
Among the animals, sponges, flatworms (Planaria) and tapeworm shows fragmentation of the body. The fragments develop into new individuals.

It is a common method of reproduction in non-flowering plants (the plants which do not produce seeds) e.g., fungi (Mucor, Rhizopus, Penicillium), bacteria, ferns or mosses.
In fungi, during spore formation, a structure called sporangium develops from the hyphae.
The nucleus in the sporangium divides repeatedly. Each nucleus gets surrounded by a small portion of cytoplasm, and a spore is formed.
Spores are very small in size. They have thick walls.
The walls help the spores to survive adverse conditions in the environment, like high temperature, scarcity of water and lack of food

asexual reproduction revision