Reproduction is the ability of living organisms to produce living beings similar to themselves.
Importance of variation:
• Sexual reproduction provides great scope for variation.
• Variation is important for survival of species.
• Variation helps a species to adapt to different environmental changes.
Kinds/types of reproduction:
- Sexual reproduction.
- Asexual reproduction
|Asexual reproduction||Sexual reproduction|
|It does not involve formation of gametes.||It involves the formation of special reproductive cell called gametes.|
|New organism are formed either by the division of the parent body or by the differentiation of the parent body.||Male and female gametes fuse to form zygote which develops into a new individual.|
Modes of Asexual reproduction:
Plants and animals from lower classes reproduce by asexual methods.
1. Binary Fission:
• Most common method in unicellular organisms.
• It is division of the parent cell into two identical daughter organisms.
• Example: Amoeba, paramecium, bacterium etc.
• Parent cell divides to produce many identical new individuals.
• Example: Plasmodium vivax, Leishmania etc.
• Adult organisms, on maturation break up into smaller fragments. Each fragment develops into new individual.
• Example: Spirogyra
• A small outgrowth called a bud arises on the parent’s body.
• The bud grows by repeated cell divisions.
• It then breaks off from the parents body and develops into a new individual.
• Example: Hydra, Sponges, Corals, Yeast etc.
• Regeneration is the ability of organisms to generate lost or damaged body parts.
• Regeneration is carried out by specialized cell or tissue.
• These form a mass of cells which undergo changes to form cells specialized in different functions.
• If planaria is cut into small pieces, then each piece develops into a new planaria.
• Example: Lizard, Starfish, Planaria, Hydra etc.
• Spores are special structures produced in sacs called sporangia.
• When spores mature, sporangia burst and spores are carried by air or water to different places.
• When spores fall on a suitable ground they germinate and give arise to new plants.
• Example: Moss, Fern, Fungi etc.
• Several plants are capable of producing naturally through their roots, stems and leaves. Such type of reproduction is called vegetative propagation.
• Example: Sweet potato (by roots), Bryophyllum (by leaves), Ginger (by stem).
Different methods used to develops plants which can bears fruits and flowers by vegetative propagation are as follow:
1.Stem cutting: This involves cutting a part of the stem and planting it the soil to allow the growth of roots and buds into shoots.
• Examples: Sugarcane, Pear, China rose etc.
2.Grafting: In grafting, the stem or bud of two best quality plants is combines to form a new plant.
• Example: Guava, Apple, Mango etc.
3.Layering: In this the lower branch of a plant is bent and covered with soil. Once new root start on the branch, it is cut from the parent plant and allowed to grow as an individual plant.
• Example: Rose, Jasmine etc.
Advantages of vegetative reproduction
• New plants show the exact characteristics as those of the parents’ plant.
• This method is faster and certain.
Plants not capable of producing sexually can be produced by this method.
• Examples: seedless bananas and grapes.
Disadvantages of vegetative reproducing
There is no possibility of variation.
The new plant grow in the same area as the parent plant which leads to competition
• Cells from the growing tips of a plant are separated and are grown on a nutrient medium containing all nutrients and hormones necessary for plant growth.
• These cells from a mass called callus.
• The callus develops plantlets.
These are transferred to the soil and grow new individuals.
Advantages of tissue culture:
• The new plantlets can be grown in a short amount of time.
• Only a small amount of initial plant tissue is required.
• The new plantlets and plants are more likely to be free of viruses and diseases.
• The process is not dependant on the seasons and can be done throughout the year.
• You need only a relatively small space to perform the process.
On a larger scale, the tissue culture process helps to supply the consumer market with new subspecies and variety.
• People looking to cultivate challenging plants such as specific breeds of orchid find more success with the tissue culture process than traditional soil.
Disadvantages of tissue culture:
• Tissue Culture can require more labor and cost more money.
• There is a chance that the propagated plants will be less resilient to diseases due to the type of environment they are grown in.
It is imperative that, before being cultured, the material is screened; failure to pick up any abnormalities could lead to the new plants being infected.
• While the success rate is high if the correct procedures are followed, success with the tissue culture is not a guarantee.