CHAPTER 2.
REPRODUCTION IN LOWER AND HIGHER ANIMALS
Ø The Process of formation of
new individuals of same species for continuity of race is called as
reproduction.
Ø Importance of
Reproduction.
Ø It helps to continue
the race and inheritance of characters from parents to offsprings.
Ø It helps to continue
the life generation after generations.
Ø Sexual reproduction
brings about variation of characters in offsprings.
Ø Sexual reproduction
plays major role in evolution of species.
Ø Definition:
Ø Development of new
individuals without formation and fusion of gametes is called as asexual
reproduction.
Ø It is characteristic
feature of lower organisms.
Ø Basic features of
Asexual Reproduction.
Ø Found only in lower
organisms.
Ø Most primitive and
simplest method of reproduction.
Ø Only mitotic division
takes place
Ø Process is uniparental
i.e. involves single parent.
Ø Offsprings produced are
genetically identical to parents.
Ø The process never
develops any variation hence plays no role in evolution.
Ø It does not involve
formation and fusion of gametes. It is
rapid method of multiplication.
|
Asexual
reproduction |
Sexual
Reproduction |
|
1. It
is always uniparental process |
1) It is always biparental process. |
|
2.
Gametes are not involved. |
2) Gametes are involved. |
|
3.
Only mitotic division takes place. |
3) Both mitotic and meiotic division take
place. |
|
4. Cells
involved are somatic. |
4) Cells involved are germ cells. |
|
5.
Offsprings are genetically identical. |
5) Offsprings show variation. |
|
6. No
role in evolution. |
6) Plays major role in evolution. |
|
7. It
is rapid process. |
7) It is slow process. |
|
8. Unit of reproduction is entire body or body
part. |
8) Unit of
reproduction is gametes |
|
9. Found only in
lower organisms. |
9) Found in higher
plants and animals. |
Ø Gemmule
formation:-
Ø It is a method or
asexual reproduction.
Ø Gemmule formation is a
type of endogenous budding in fresh water sponges.
Ø Each gemmule is a mass
of undifferentiated cells called as archaeocytes surrounded by a protective coat of amphidisk spicules.
Ø The coat is hard and
chitinous in nature.
Ø The gemmule formation
helps in perennation and dispersal.
Ø During favourable
conditions, archaeocytes come out of gemmule through micropyle and form a new sponge. E.g. spongilla.
Ø The mechanism of
asexual reproduction in which one or more unicellular or multicellular outgrowths called
as buds are formed on the body is known as budding.
Ø Each multicellular outgrowth,
bud enlarges, develops the parental characters and then separates to
lead independent life.
Ø It feeds, grows and
develops as adult and repeats the
process.
Ø E.g. Hydra.
Ø Planarians show
regeneration.
Ø The anterior part
exerts a pull over the posterior part which holds on.
Ø Due to this the middle part constricts and finally breaks.
The anterior part regenerates the posterior part and
vice-versa.
Ø Thus, at the end two
complete worms are developed at the end.
1)
What
is reproduction?
2)
Which
is the most distinguishing character of living organism?
3)
What
are the two basic patterns of reproduction?
4)
Which
type of division take place during asexual reproduction?
5)
What
is the nature of offspring produced in asexual reproduction?
6)
Which
is the quick method of multiplication?
7) Give the examples of animals which show asexual reproduction?
8) What is clone?
9) What can be the possible reasons of variation produce during asexual reproduction?
10) Which cells produce gemmules?
11) What is the role of archeooytes?
12) Why organisms show gemmule formation?
13) Give the examples of animals which show gemmule formation?
14) Which groups of animals are show Budding?
15) Give examples of Budding?
16) Which type of budding is found in hydra?
17) Which organism shows regeneration?
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