How do Organisms Reproduce?
Introduction
Reproduction is the process by which living organisms produce new individuals similar to themselves.
It ensures continuity of life on earth.
NEED
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.
For example- If temperature of water increases (due to global warming) drastically, bacteria will die. But if
some variants are resistant to heat, they will survive.
Types of Reproduction
Asexual Reproduction Sexual Reproduction
A single individual give rise to new individual. Two individuals i.e., one male and one female are
0
Gametes are not formed. needed to give rise to new individual.
.
New individual is identical to parent. Gametes are formed.
It is extremely useful as a means of rapid New individual is genetically similar but not identical
multiplication.
Adopted by lower organisms.
to parents.
2
It is useful to generate more variations in species.
g
Adopted by higher organisms.
in
rn
ea
e L Modes of Asexual Reproduction
tiv
The parent cell divides into daughter cells.
1. Binary Fission
a
Seen in bacteria, protozoa like Amoeba, Paramecium.
The cell division can occur in any plane as in case of Amoeba. However, organisms like Leishmania, which have a
e
whip like flagella at one end, binary fission occurs in a definite orientation in relation to the flagellum.
r
C
Cytokinesis: Division of cytoplasm.
Karyokinesis: Division of Nucleus.
22
, 2. Multiple Fission
In this during unfavourable conditions, the parent cell develops a thick resistant wall around itself forming a
cyst.
Within the wall, the cytoplasm divides many times to form many plasmodia.
When conditions become favourable, the cyst wall breaks and the Plasmodium are released.
e.g. Plasmodium
0
3. Budding
Organisms like Hydra & reproduce through budding, utilizing regenerative cells.
2.
A bud develops as an outgrowth due to repeated cell division at a specific site on the parent organism.
Buds mature into independent individuals and detach from the parent body.
ng
ni
ar
Le 4. Fragmentation
e
In some multi-cellular organisms with simple body organization,
v
fragmentation is a method of reproduction.
i
Example: Spirogyra breaks into smaller pieces upon maturation,
t
which grow into new individuals.
Not all multi-cellular organisms can divide cell-by-cell due to
ea
complex body organization.
Organisms with specialized cells organized into tissues and organs
r
require more complex reproductive methods.
5. Regeneration
C
Fully differentiated organisms can regenerate new individuals from body parts.
Example: Hydra and Planaria can regenerate from cut pieces.
Regeneration involves specialized cells proliferating and
differentiating into various cell types and tissues.
It is a process distinct from reproduction as most organisms
do not rely on being cut up to reproduce.
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Introduction
Reproduction is the process by which living organisms produce new individuals similar to themselves.
It ensures continuity of life on earth.
NEED
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.
For example- If temperature of water increases (due to global warming) drastically, bacteria will die. But if
some variants are resistant to heat, they will survive.
Types of Reproduction
Asexual Reproduction Sexual Reproduction
A single individual give rise to new individual. Two individuals i.e., one male and one female are
0
Gametes are not formed. needed to give rise to new individual.
.
New individual is identical to parent. Gametes are formed.
It is extremely useful as a means of rapid New individual is genetically similar but not identical
multiplication.
Adopted by lower organisms.
to parents.
2
It is useful to generate more variations in species.
g
Adopted by higher organisms.
in
rn
ea
e L Modes of Asexual Reproduction
tiv
The parent cell divides into daughter cells.
1. Binary Fission
a
Seen in bacteria, protozoa like Amoeba, Paramecium.
The cell division can occur in any plane as in case of Amoeba. However, organisms like Leishmania, which have a
e
whip like flagella at one end, binary fission occurs in a definite orientation in relation to the flagellum.
r
C
Cytokinesis: Division of cytoplasm.
Karyokinesis: Division of Nucleus.
22
, 2. Multiple Fission
In this during unfavourable conditions, the parent cell develops a thick resistant wall around itself forming a
cyst.
Within the wall, the cytoplasm divides many times to form many plasmodia.
When conditions become favourable, the cyst wall breaks and the Plasmodium are released.
e.g. Plasmodium
0
3. Budding
Organisms like Hydra & reproduce through budding, utilizing regenerative cells.
2.
A bud develops as an outgrowth due to repeated cell division at a specific site on the parent organism.
Buds mature into independent individuals and detach from the parent body.
ng
ni
ar
Le 4. Fragmentation
e
In some multi-cellular organisms with simple body organization,
v
fragmentation is a method of reproduction.
i
Example: Spirogyra breaks into smaller pieces upon maturation,
t
which grow into new individuals.
Not all multi-cellular organisms can divide cell-by-cell due to
ea
complex body organization.
Organisms with specialized cells organized into tissues and organs
r
require more complex reproductive methods.
5. Regeneration
C
Fully differentiated organisms can regenerate new individuals from body parts.
Example: Hydra and Planaria can regenerate from cut pieces.
Regeneration involves specialized cells proliferating and
differentiating into various cell types and tissues.
It is a process distinct from reproduction as most organisms
do not rely on being cut up to reproduce.
23
