Hey students so as you know that
 
reproduction is a means to produce new
 
Offsprings. These offsprings or
 
organisms produces are very much similar
 
to their parents. But we know that there
 
are subtle differences between the
 
parents and the offsprings. Let us learn
 
why this happens? We know that the
 
chromosome present in the nucleus of the
 
cell, contains the information of
 
inheritance in the form of DNA. And the
 
DNA expresses this information in the
 
form of protein. So the basic event in
 
reproduction is to make a copy of this
 
DNA. Now, the copy of this DNA is made by
 
some biochemical reactions and as we
 
know that no reaction can create an
 
exact copy of the DNA rather some errors
 
are always expected. And this will
 
produce some variations which will occur
 
in the progeny.
 
Now the question arises that what is the
 
importance of these variations.
 
Well, we know that there can be some
 
changes in the environment around the
 
organisms. For example, temperature can go
 
up or down, water presence may change etc.
 
Now, if the population of an organism is
 
well-suited for a particular environment
 
and it that environment changes the
 
whole population is more likely to be
 
wiped out. But if there are some
 
variations in the populations, those
 
variations can help in the survival of
 
that population in that changing
 
environment. And so we say that
 
variations are useful for a population.
 
Having discussed that how these
 
variations are produced in these progenies.
 
And what is their importance,
 
Let's see different modes by which these
 
progenies are produced. The process of
 
production
 
of progenies or offsprings is
 
known as reproduction. Now this
 
reproduction occurs either by a single
 
individual or by the involvement of
 
both the sexes. That is by the
 
involvement of both, male and female. When
 
the reproduction occurs by a single
 
individual it is known as asexual
 
reproduction. While when the reproduction
 
occurs with the involvement of both the
 
sexes that is male and female it is
 
known as sexual reproduction. In this
 
lesson we'll mainly study about asexual
 
reproduction there are various methods
 
by which individuals divide asexually.
 
For example, fission, fragmentation
 
regeneration, budding, vegetative
 
propagation and spore formation. We'll
 
discuss all of them one by one
 
Let's start with fission, fission means
 
dividing or splitting. So in this the
 
organism divides or splits as a whole. It
 
is mainly found in all unicellular
 
organisms. There are two types of fissions.
 
First, binary fission second multiple
 
fission. Now in binary fission the
 
organism divides or splits in two parts.
 
For example, it occurs in bacteria, amoeba
 
paramecium, etc. Depending on the plane of
 
cell division, binary division can be of
 
three types. First, organism can split from
 
Tranverse plane. For example, in bacteria,
 
protozoa, etc. Second organisms can split
 
from any plane. For example in Amoeba and
 
third, organisms can split longitudinally.
 
For example, in leishmania. It is also
 
known as
 
kala-azhar. It is a protozoan. So it has a
 
whip like structure called flagellum.
 
at the end of itself and that's to divide
 
the cell into two equal halves it has to
 
divide longitudinally. A second type of
 
fission is multiple vision. In which the
 
organisms divide into many. So some
 
organisms they have continuous division
 
and produce many daughter cells
 
simultaneously. For example, malarial
 
parasite, plasmodium. Next method of
 
asexual reproduction is fragmentation. It
 
is mainly present in multicellular
 
organisms with simple body organization.
 
For example, in spirogyra. It is a
 
green algae. It has filamentous
 
structure. When it matures it breaks down
 
into various elements or pieces and
 
these pieces then give rise to the new
 
individuals. Now we'll see what is
 
regeneration. In this process fully
 
diifferentiated organisms give rise to new
 
organisms from their body parts. They do
 
this with the help of specialized cells.
 
Which can make all the types of cells in
 
the body.
 
Hydra and planaria show regeneration we
 
can see regeneration process in planaria.
 
If the body of the planaria is cut
 
into many pieces, then each piece will
 
grow into a new individual. Next method
 
is budding. It is also present in hydra.
 
Regenerative cells in hydra are
 
responsible for budding. This budding is
 
the result of repeated cell division at a
 
particular site. It is nothing but just
 
an outgrowth. When this bud matures, they
 
detached from the body of the parents
 
and then
 
they grow as new individuals. Next we
 
study about vegetative propagation. This
 
type of reproduction occurs in plants.
 
When new plants are developed from
 
vegetative parts of the plant, like roots,
 
stems and leaves. It is known as
 
vegetative propagation. Vegetative
 
propagation occurs naturally in many
 
plants, for example, in bryophyllum.
 
You might have seen the lives of bryophyllum.
 
It has buds all around its margins. When
 
these leaves fall into soil, new plants
 
emerge. There are many advantages of
 
vegetative propagation. Like first, the
 
plants can bear fruits and flowers at
 
much earlier stage than other plants.
 
Second, the plants which have lost the
 
capacity to bear seeds, can also grow for
 
example, banana, rose, jasmine, etc. And third
 
the plants produced by this method are
 
genetically similar to the parents and
 
so they share the same characteristics.
 
Nowadays many farmers and gardeners are
 
using artificial methods of vegetative
 
propagation like cutting, grafting,
 
layering, etc. By these methods many
 
plants like Rose, grapes, sugarcane, etc are
 
grown. You might be amazed to know that
 
scientists and plant biologists have
 
found new techniques to grow plants they
 
remove the cells or tissues from the
 
growing tip of the plants and place
 
these cells or tissues in artificial
 
medium. After repeated division, a mass of
 
cells is formed in this medium. This
 
mass of cells is known as callus. This
 
callus is then again place in another
 
artificial medium which contains
 
hormones for its growth and
 
differentiation. From this callus
 
plantlets are seen to be growing out and
 
these plantlets are planted in soil for
 
for the plant development. This technique
 
of growing plants is known as tissue
 
culture. By this technique, many plants
 
can be grown by a single plant in
 
disease free conditions. Many ornamental
 
plants are grown by using this tissue
 
culture technique.
 
Lastly we'll study about spore formation.
 
If you keep a wet bread slice for 3-4 hours in
 
cool, moist and dark place. You'll find a
 
greenish appearance on it.
 
These greenish substances are fungus or
 
bread mold called rhizopus. This rhizopus
 
has hyphae and sporangia in it. If you
 
observe it with magnifying glasses,
 
You'll find this type of structure. These
 
filaments are called hyphae. These are
 
non- reproductive structures of
 
rhizopus. While this blob on a stick like
 
structure is called sporangia. These are
 
the reproductive structures of rhizopus.
 
This sporangia contains spores in them.
 
And these spores are surrounded by a thick
 
wall, which protects it. Dehiscence
 
these spores in moist environment
 
develops new rhizopus. So in this lesson
 
we learned that how variations occur in
 
the progenies and why they're important.
 
Next we saw about the modes of
 
asexual reproduction. Which are fission,
 
fragmentation, regeneration, budding,
 
vegetative propagation and spore
 
formation.
