Online Notes on Chapter=8 ( How do Organisms Reproduce) Part 1

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.

(ii) Fragmentation : The organism breaks-up into smaller pieces upon
maturation, each piece develops into new individual. E.g., Spirogyra

(iii) Regeneration : If organism is somehow cut or broken into many pieces,
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

(v) Vegetative Propagation : In many plants, new plants develops from
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.

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