Class 8, Science, Chapter-6, Lecture-1, Asexual Reproduction (Notes)
REPRODUCTION:
The process by which new individuals of the same species are produced by the existing organisms is termed as reproduction.
TYPES OF REPRODUCTION:
- ASEXUAL REPRODUCTION:
The mode of reproduction in which the body cells of an organism undergo mitotic division and form two or more new individuals of the same kind is termed as asexual reproduction.
METHODS –
- Fission
(a) Binary fission
(b) Multiple fission - Budding
- Spore Formation
- Regeneration
- Vegetative Propagation
- SEXUAL REPRODUCTION:
The mode of reproduction in which male sex cells and female sex cells undergo fusion to produce zygote which further divides to form new organism is termed as sexual reproduction.
BINARY FISSION: (in unicellular Organism like Amoeba, Paramecium)
The process of asexual reproduction in which a unicellular organism divides into two daughter cells and each one grows into adult organism is termed as binary fission.
STEPS:
- The nucleus of the parent cell divides into two.
- A constriction appears in the cell membrane
- Constriction increases and cytoplasm divides into two parts
- Two daughter organisms are formed.
MULTIPLE FISSION: (in Plasmodium)
STEPS:
- The nucleus divides into many daughter nuclei.
- The nuclei arrange along the periphery of the parent cell.
- An outer membrane develops around each nucleus with some cytoplasm
- The multinucleated cell divides and daughter organisms are formed.
BUDDING: (in Hydra, Yeast)
The process of asexual reproduction in which a small part of the body of the parent organism grows out as a bud and separates after developing into an organism is termed as budding.
STEPS:
- A bulging bud on the body appears due to repeated mitotic division.
- The bud enlarges and develops.
- The developed bud separates from the body and develops into daughter organism.
SPORE FORMATION: (in Rhizopus, Mucor, Penicillium)
The process of asexual reproduction in which the parent plant produces a large number of spores that can produce new plants is called spore formation.
(This is the most common method of asexual reproduction in Fungi and Bacteria)
STEPS:
- Sporangium develops at the top of vertical hypha.
- The nucleus divides inside the sporangium.
- Each nucleus with a bit of cytoplasm, develops into spore.
- The sporangium breaks and spores are liberated.
- The spores develop into new hypha under suitable conditions.
REGENERATION: (in Spirogyra, Hydra, Planaria, Sponges)
The method of asexual reproduction in which a mature organism develops from detached body part of the parent organism is called regeneration.
STEPS:
- The mature organism breaks into two or more pieces.
- Each piece grows into a new individual.
VEGETATIVE PROPAGATION: (in Guava, Bryophyllum, Onion, Banana, Garlic, Water Hyacinth)
The method of asexual reproduction in which new plants are obtained from stem, root or leaf of old plants is termed as vegetative propagation.
ADVANTAGES OF VEGETATIVE PROPAGATION:
- Plants which produce very few seeds can be grown by vegetative propagation.
- Very young plants can be made to flower by grafting them on mature plants.
Differences between:
Fission | Fragmentation |
---|---|
Fission takes place in UNICELLULAR organism. | Fragmentation takes place in simple MULTICELLULAR organisms. |
In the process, nucleus divides first and then the cytoplasm divides to produce two individuals. | In the process, mature organism first breaks and then develops into new individual by cell division. |