How do organisms reproduce?- Asexual Reproduction Notes

HOW DO ORGANISM REPRODUCE

˜ Reproduction is the process by which living organisms produce new

individuals similar to themselves.

˜ Reproduction ensured continuity of life on earth.

˜ Reproduction – A bridge to hereditary transmission.

˜ It involves continuation of characters from the parents to daughter cells

by Copying of DNA (Deoxyribose Nucleic Acid) molecules present in

the chromosomes of the cell.

˜ Copying of DNAs is also not a foolproof exercise, even minute changes

bring about Variation in the blue print of the offsprings.

˜ The useful variations are retained while the harmful one does not go

beyond.

˜ Actually variations help the species to withstand drastic environmental

changes, thus save the species from becoming extinct and promotes its

survival for a longer time.

˜ This inbuilt tendency of variation is the ‘‘fuel’’ for Evolution.

                                              

                                                      REPRODUCTION

    

Asexual Reproduction	Sexual Reproduction
1. A single parent is involved	1. Both Parents involved
2. Gametes not formed	2. Gametes are formed
3. Progeny is Identical to parent eg. Fission in Amoeba	3. Progeny is only genetically similar to the parent.

˜ Asexual Reproduction is extremely useful as a mean of rapid multiplication. It is common in lower plants and animals

MODES OF ASEXUAL REPRODUCTION

1.      FISSION : the parent cell divides/splits into two daughter cell-Binary Fission;

                                                           splits into many cells-multiple Fission.

  

                                                              FISSION

Binary Fission	Multiple Fission
The parent cell divides into two equal halves (daughter cells) E.g. Amoeba, Leishmania, Paramecium	The parent cell divides into many daughter cell simultaneously. Eg. Plasmodium

Stages:

Nucleus lengthens -  nucleus divides- cytoplasm divides- daughter amoebae formed

2.      BUDDING : A bud develops as an outgrowth on parent body due to repeated cell division at a specific site. These buds develop into tiny individuals, which detach from parent body when they mature.

              Eg. Hydra, yeast.

3.      Spore Formation : Spores are small, bulb like structure that develop in sporangium at the top of the erect hyphae of the fungus. They are released into the air and germinate, into new individuals after landing into food or soil.

4.       FRAGMENTATION : It is the accidental process when the broken pieces of an organism (fragments) grow into a complete organism.

5.      REGENERATION : When the simple animals like Hydra, Planaria are cut into parts , each part develops into whole new individual by regenerating lost body parts. This is known as regeneration. It is carried out by specialised cells which divide and differentiate to form the complete individual.

6.      Vegetative Propagation: A mode of reproduction in many plants in which vegetative parts like stem, root, leaves develop into new plant under favourable conditions.

     Methods of Vegetative Propagation

1. By Roots : Eg. adventitious roots of Dahlias

2. By Stems : Eg. Potato (tuber), ginger (rhizome)

3. By Leaves : Eg. leaves of bryophyllum bear adventitious buds (in the notches of leaf margin) which develop into new plants.

4. Grafting : Eg. Mango.

5. Stem Cutting : Eg. Rose

6. Layering : Eg. Jasmine

7. Tissue culture : Eg. Orchids, Ornamental Plants.

Benefits of Vegetative Propagation

1. Plants can bear flowers, fruits earlier than those produced from seeds.

2. Helps in growing plants like Banana, orange, rose, jasmine that have lost the

  capacity to produce seeds.

3. Genetical similarity is maintained in the plants.