How do organisms Reproduce – Notes
Asexual Reproduc on
• It involves only one parent.
• There are no forma on and fusion of gametes.
• The young ones formed are almost iden cal to each other as well as to the parent cell.
• Asexual reproduc on generally occurs during favorable environmental condi ons and
when there is an abundance of food.
• It is a faster method of reproduc on.
Types of Asexual Reproduc on is Unicellular Organism
(i) Binary Fission: Seen in bacteria, protozoa like Amoeba, Paramecium. (In these first
pseudopodia withdrawn (karyokinesis) the nucleus of the parent cell divides and then the
cytoplasm divides (cytokinesis) resul ng in the forma on of two daughter cells). It occurs
during highly favourable condi ons. The cell division can occur in any plane as in case of
Amoeba. However, organisms like Leishmania. (cause Kala-azar), which have a whip like
flagella at one end, binary fission occurs in a definite orienta on in rela on to the flagellum.
Cytokinesis: Division of cytoplasm.
Karyokinesis: Division of Nucleus.
(ii) Mul ple Fission: Seen in Plasmodium, (a malarial parasite). In this during unfavorable
condi ons, the parent cell develops a thick resistant wall around itself forming a cyst. Within
the wall, the cytoplasm divides many mes to form many plasmodia. When condi ons
become favorable, the cyst wall breaks and the Plasmodium are released.
, Types of Asexual Reproduc on in Mul cellular Organisms:
(iii) Fragmenta on: Seen in mul cellular organisms which have a rela vely simple body
organiza on like Spirogyra. Spirogyra has a filamentous body. (If it breaks into smaller pieces
or fragments). Each fragment has the capacity to form a new individual.
However, all mul cellular organisms cannot show cell-by-cell division as cells from ssues
which form organs. These organs are placed at definite posi ons in the body. Hence, they
need to use more complex methods of reproduc on.
(iv) Regenera on: It is the ability of organisms to develop their lost parts. Some organisms
show have high regenera ve capacity it is also a means of reproduc on for example;
Planaria. (Regenera on is carried out by specialized cells which redivide to form a mass of
cells from which different cells undergo changes to become different cell types and ssues.
These changes occur in an organized sequence known as development).
(v) Budding: Seen in Hydra. Parent Hydra develops a bud at its lower end. This grows in size
and finally breaks off to live independently.
(vi) Spore Forma on: Seen in Rhizopus (a fungus). Rhizopus body is made up of thread-like
structures called hyphae. The erect hyphae bear sporangia inside which reproduc ve
structures called spores are formed. Spores are asexually reproducing bodies having a thick
Asexual Reproduc on
• It involves only one parent.
• There are no forma on and fusion of gametes.
• The young ones formed are almost iden cal to each other as well as to the parent cell.
• Asexual reproduc on generally occurs during favorable environmental condi ons and
when there is an abundance of food.
• It is a faster method of reproduc on.
Types of Asexual Reproduc on is Unicellular Organism
(i) Binary Fission: Seen in bacteria, protozoa like Amoeba, Paramecium. (In these first
pseudopodia withdrawn (karyokinesis) the nucleus of the parent cell divides and then the
cytoplasm divides (cytokinesis) resul ng in the forma on of two daughter cells). It occurs
during highly favourable condi ons. The cell division can occur in any plane as in case of
Amoeba. However, organisms like Leishmania. (cause Kala-azar), which have a whip like
flagella at one end, binary fission occurs in a definite orienta on in rela on to the flagellum.
Cytokinesis: Division of cytoplasm.
Karyokinesis: Division of Nucleus.
(ii) Mul ple Fission: Seen in Plasmodium, (a malarial parasite). In this during unfavorable
condi ons, the parent cell develops a thick resistant wall around itself forming a cyst. Within
the wall, the cytoplasm divides many mes to form many plasmodia. When condi ons
become favorable, the cyst wall breaks and the Plasmodium are released.
, Types of Asexual Reproduc on in Mul cellular Organisms:
(iii) Fragmenta on: Seen in mul cellular organisms which have a rela vely simple body
organiza on like Spirogyra. Spirogyra has a filamentous body. (If it breaks into smaller pieces
or fragments). Each fragment has the capacity to form a new individual.
However, all mul cellular organisms cannot show cell-by-cell division as cells from ssues
which form organs. These organs are placed at definite posi ons in the body. Hence, they
need to use more complex methods of reproduc on.
(iv) Regenera on: It is the ability of organisms to develop their lost parts. Some organisms
show have high regenera ve capacity it is also a means of reproduc on for example;
Planaria. (Regenera on is carried out by specialized cells which redivide to form a mass of
cells from which different cells undergo changes to become different cell types and ssues.
These changes occur in an organized sequence known as development).
(v) Budding: Seen in Hydra. Parent Hydra develops a bud at its lower end. This grows in size
and finally breaks off to live independently.
(vi) Spore Forma on: Seen in Rhizopus (a fungus). Rhizopus body is made up of thread-like
structures called hyphae. The erect hyphae bear sporangia inside which reproduc ve
structures called spores are formed. Spores are asexually reproducing bodies having a thick
