This is Online Notes on Chapter=8 (How do Organisms Reproduce) Part 1 for preparation of CBSE BOARD Examination, NTSE etc.• Reproduction is the process by which living organisms produce new
individuals similar to themselves. It ensures continuity of life on
earth.
• Nucleus of the cell contains DNA (Deoxyribose Nucleic Acid) which
is the heredity material.
• DNA replicates and forms new cells causing variation. So, these new
cells will be similar but may not be identical to original cell.
• Variations are useful for the survival of the individual and species
over time as well as basis for evolution.
Types of Reproduction :
(a) Asexual Reproduction
• A single individual give rise to new individual.
• Gametes are not formed.
• New individual is identical to parent.
• It is extremely useful as a means of rapid multiplication.
• Adopted by lower organisms.
(b) Sexual Reproduction
• Two individuals i.e., one male and one female are needed to give rise
to new individual.
• Gametes are formed.
• New individual is genetically similar but not identical to parents.
• It is useful to generate more variations in species.
• Adopted by higher organisms.
Modes of Asexual Reproduction:
(i) Fission : The parent cell divides into daughter cells.
• Binary fission : 2 cells are formed. E.g., amoeba.
• Multiple fission : Many cells are formed. E.g., Plasmodium.
maturation, each piece develops into new individual. E.g., Spirogyra
each piece grows into a complete organism. E.g., Planaria, Hydra.
(iv) Budding : A bud is formed which develops into tiny individual. It
detaches from parent
vegetative parts such as :
• By roots : E.g., dahlias, sweet potato.
• By stem : E.g., potato, ginger.
• By leaves : E.g., bryophyllum (leaf notches bear buds which develop
into plants).
• Artificial methods :
(a) Grafting : E.g., Mango
(b) Cutting : E.g., Rose
(c) Layering : E.g., Jasmine
(d) Tissue culture : New plants are grown by using growing tip of a plant.
These growing cells are kept in a culture medium leads to the formation of
callus. Callus is then transferred to hormone medium which causes growth and
differentiation. E.g., ornamental plants, orchid.
Benefits of tissue culture :
• We can grow plants like banana, rose, jasmine etc. that have lost the
capacity to produce seeds.
• New plants are genetically similar to parents.
• Helps in growing seedless fruits.
(v) Spore Formation : Spores are small bulb like structures which are
covered by thick walls. Under favourable conditions, they germinate and
produce new organism.
