Revision Notes
Class - 12 Biology
Chapter 1 – Reproduction in Organisms
Life Span: The period which begins from birth and ends with the natural death of
an organism is known as its life span.
Reproduction is an important biological process by which an organism will give
rise to another organism similar to itself.
Some basic facts about reproduction are discussed below.
Reproduction is the process that ensures that species are continued from
generation to generation. It leads to the development of genetic vavariation.
This variation in genetics is inherited during reproduction.
Reproduction in which only one parent is called asexual.
Reproduction in which two parents of the opposite sex are involved in the
fusion of male and female gametes is known as sexual reproduction.
Asexual Reproduction Sexual Reproduction
Class XII Biology www.vedantu.com 1
,ASEXUAL REPRODUCTION
In this asexual reproduction, only one parent participates in producing the
offspring. As a result, the offspring produced are identical to each other and
also to the parents.
Asexual reproduction is most commonly seen in unicellular organisms, as well
as in plants and animals with relatively simple organizations. It is also seen in
organisms that are multicellular.
ASEXUAL REPRODUCTION IN ANIMALS
The most commonly seen modes of asexual reproduction in the case of animals
are as follows:
1. Fission:
Fission, commonly known as binary fission, takes place in prokaryotic
microorganisms and a few multicellular organisms too.
After a growth period, the organism is split into independent organisms. Some
single-celled eukaryotes go through binary division via mitosis.
In different organisms, part of an individual is separated and a second
individual is formed.
For example, in lots of asteroid echinoderms, this technique takes place while
the central disk separates.
Some sea anemones and a few polyps also reproduce via division.
In some cases, it is seen that the nucleus divides several times by amitotic
divisions. This leads to the formation of several new copies of nuclei.
Cytoplasmic division does not take place during this time. The cytoplasm will
accumulate around each nucleus. Therefore, many unicellular and seedless
offspring are formed from a single cell. This method of propagation is known
as multiple fission. Eg Amoeba and Paramecium.
Class XII Biology www.vedantu.com 2
, Differences between binary and multiple fission-
S.No. Characteristics Binary Fission Multiple Fission
1 Number of Parents divide into Parent divide in many
daughters produced two daughters. daughters.
2 Time of Formation During favorable During unfavorable
conditions. conditions.
3 Fate of Parent Nothing is left with Residual cytoplasm is left.
parents.
2. Budding
The budding is a type of asexual reproduction that occurs from the growth of
part of a cell or a region of the body that leads to the separation of the original
organism into two individuals.
The budding process is common in some invertebrates such as corals and
hydras.
Class XII Biology www.vedantu.com 3
Class - 12 Biology
Chapter 1 – Reproduction in Organisms
Life Span: The period which begins from birth and ends with the natural death of
an organism is known as its life span.
Reproduction is an important biological process by which an organism will give
rise to another organism similar to itself.
Some basic facts about reproduction are discussed below.
Reproduction is the process that ensures that species are continued from
generation to generation. It leads to the development of genetic vavariation.
This variation in genetics is inherited during reproduction.
Reproduction in which only one parent is called asexual.
Reproduction in which two parents of the opposite sex are involved in the
fusion of male and female gametes is known as sexual reproduction.
Asexual Reproduction Sexual Reproduction
Class XII Biology www.vedantu.com 1
,ASEXUAL REPRODUCTION
In this asexual reproduction, only one parent participates in producing the
offspring. As a result, the offspring produced are identical to each other and
also to the parents.
Asexual reproduction is most commonly seen in unicellular organisms, as well
as in plants and animals with relatively simple organizations. It is also seen in
organisms that are multicellular.
ASEXUAL REPRODUCTION IN ANIMALS
The most commonly seen modes of asexual reproduction in the case of animals
are as follows:
1. Fission:
Fission, commonly known as binary fission, takes place in prokaryotic
microorganisms and a few multicellular organisms too.
After a growth period, the organism is split into independent organisms. Some
single-celled eukaryotes go through binary division via mitosis.
In different organisms, part of an individual is separated and a second
individual is formed.
For example, in lots of asteroid echinoderms, this technique takes place while
the central disk separates.
Some sea anemones and a few polyps also reproduce via division.
In some cases, it is seen that the nucleus divides several times by amitotic
divisions. This leads to the formation of several new copies of nuclei.
Cytoplasmic division does not take place during this time. The cytoplasm will
accumulate around each nucleus. Therefore, many unicellular and seedless
offspring are formed from a single cell. This method of propagation is known
as multiple fission. Eg Amoeba and Paramecium.
Class XII Biology www.vedantu.com 2
, Differences between binary and multiple fission-
S.No. Characteristics Binary Fission Multiple Fission
1 Number of Parents divide into Parent divide in many
daughters produced two daughters. daughters.
2 Time of Formation During favorable During unfavorable
conditions. conditions.
3 Fate of Parent Nothing is left with Residual cytoplasm is left.
parents.
2. Budding
The budding is a type of asexual reproduction that occurs from the growth of
part of a cell or a region of the body that leads to the separation of the original
organism into two individuals.
The budding process is common in some invertebrates such as corals and
hydras.
Class XII Biology www.vedantu.com 3
