REPRODUCTION IN ORGANISMS -01 For Class 12th and AIPMT
Articles Blog

REPRODUCTION IN ORGANISMS -01 For Class 12th and AIPMT


Hi,
This is Dr. Neela Bakore, And we are starting with the first chapter
in the unit of Reproduction. The first chapter is REPRODUCTION IN ORGANISM. Reproduction is a process of giving rise to
new organisms of the same kind. This is the basic characteristics feature of living
organisms, Even viruses which are kept between living
and non living, They also show this process,
A life process that is Reproduction. The basic reason for reproduction is continuity
of the race. So why do organism reproduce? Because they want to continue their race. So that the race continues for times to come. Continuity of the race. This is the basic purpose of reproduction. There are two main categories in which we
divide or classify the reproduction. Asexual Reproduction and Sexual Reproduction. Asexual Reproduction is involvement of one
parent. So it is also known as uni -parental,
Whereas in sexual reproduction two parents a male and a female are required so it is
also known as bi-paternal. In asexual reproduction formation and fusion
of gamete is not required or do not takes place. So there is no fusion of gametes,
Whereas in sexual reproduction gamete formation and fusion is important part. Formation of gametes takes place by the process
of meiosis. And in meiosis genetic variation takes place
due to crossing over. Whereas in this case as no gamete are fusing
so no variation is there. So the offsprings which are there,
They are identical to the parents. So the offsprings are same as parents or
that single parent which is performing the process. Whereas in this there is genetic variation,
And the offsprings have characteristics of both the parents and there is the combination
also possible 50 – 50, 60 – 40 or even variable. So genetic variation and the offsprings are
different, Different in the sense of the characteristics. So these are basic differences,
We will take this processes in detail. Asexual reproduction is also known as apomixes. And sexual reproduction is known as amphimixes. Let us first discuss asexual reproduction
and the methods by which this takes place. Asexual reproduction takes place by various
methods. So let us first write down the names and then
take these one by one. One is fission, these fission basically is
the parent cell splits into daughter cells. It can be binary fission that means one parent
cell splits into two daughter cells. Or it could be multiple fission. Another method of asexual reproduction is
by budding, The buds normally are termed as an outgrowth
on the parent body, So most of the times which we talk of are
the buds which are outside these buds are known as exogenous. So there are two types of buds which are seen
one is exogenous and other is endogenous so exogenous budding and
endogenous budding Where the bud are inside the parent body. Fragmentation, where the parent body just
undergoes fragmentation breaks up into different fragments and each fragment gives rise to
an individual, Then spore formation there are various types
of spores, Like zoospores, conidia, oidia and all those
things. And one more when some vegetative part of
the plant is helping in reproduction, So that becomes vegetative propagation,
In vegetative propagation, we will talk about both natural as well as artificial. That is naturally the plants which show vegetative
propagation and artificially how we can help these plants propagate or we can use this
methods for propagation of the plants. So these are the categories in which we divide
the asexual reproduction basically. Let us start with fission,
So first, fission basically means splitting one is binary fission,
So one type of fission is binary fission, In which one parent cell or organism, it could
be unicellular organism splits into daughter cells. So one parent cell splits into two daughter
cells. Splitting is going to be
First the nucleus is going to split and then cytoplasm will undergo splitting,
Now the plane in which the splitting takes place we can get different types of binary
fission, Like irregular binary fission,
Irregular binary fission, irregular means there is no fixed plane in which the nucleus
or the cytoplasm is going to split. This is seen in Amoeba. In amoeba the cytoplasmic constriction takes
place or can take place in any plane. So if this amoeba has to divide or reproduce
first its nucleus will start to show constriction. Then this nucleus would completely divide
into two nuclei and cytoplasm also starts showing constrictions. And now these two daughter amoebi with their
nuclei are formed. In this case we have seen the constrictions
like this. But because of the shape of amoeba is not
fixed, It can show constriction in any plane,
It can show constriction from side, from top, anywhere
And that is why we are calling it irregular binary fission. What has happened to the parent cell? The parent cell undergoes fission to produce
two daughter cells. Technically speaking this cell has now divided
into two daughter cells which are again young, They will grow attain maturity,
At the normal size and will again divide. So these organisms which show binary fission
they are considered as immortal. Immortal because normally what happens is
reproduction then they come into post reproductive stage and then they die,
But here when it comes into reproductive phase it has given rise to two daughter cells. Now both these will grow, again they will
divide by binary fission. Again two daughter cells will be formed. So naturally they do not undergo death
And they are considered immortals. Only the ones which show binary fission. So this is one example where it is irregular. Let us talk about other type of binary fission. Again binary means parent cell will divide
into two but the plane of the division is decided. It is longitudinal,
So longitudinal binary fission. That means it is going to be vertical type
of fission. It is seen in euglena. Euglena
is a flagellate. It has one large flagellum and there is one
more smaller which is not visible to us. So when it has to divide,
First thing, it loses its flagella. The flagellum is lost. Rather both the flagella is lost. And now this upper end which is called the
gullet, Euglena is an organism which is placed between
animals and plants. It has plant like characters,
That means it has chloroplast it can perform photosynthesis. Animal like character is, it is without cell
wall. Animal cells don’t have cell wall. So, this has one characteristics of plant
and one characteristics of animal. So if it has sufficient light available to
it, it will perform photosynthesis. But if light is not available then it takes
food from outside. So it’s mode of nutrition also becomes heterotrophic,
So this is the place from where it would take nourishment or nutrition. So first thing is this upper end the gullet
end divides. So here we start seeing an organism with two
gullets formed , The upper end there are two such structures
and the lower part of the body or cell is still fused. So the splitting of cytoplasm or the constriction
is taking place from top to bottom, Or it can be termed as vertical. So after this,
These constriction deepens, This becomes even deep and ultimately we would
get two daughter euglena and now they will develop their flagella. Splitting or the plane of splitting is longitudinal
or vertical. Again one parent cell is giving rise to two
daughter cell. So that is why it is also binary fission. Because of the plane it is called longitudinal
binary fission. The third type the plane is transverse, so
it is known as transverse binary fission. The plane of cytoplasmic constriction is transverse. It is seen in paramecium. The structure of paramecium the shape is slipper
like here it has a gullet,
From here it takes the nourishment, The body is covered with Celia all along. In the gullet also there are Celia. There are two nuclei paramecium is bi-nucleate. It has a large nucleus, macro nucleus and
a smaller micro nucleus. The macro nucleus is responsible for all activities
for the cell. And micro nucleus is responsible for reproduction,
So when it has to reproduce, there are two things which are going to happen simultaneously,
The large nucleus will disintegrate that mean it will break up and dissolve into cytoplasm. Only the smaller nucleus will remain and this
smaller nucleus will split, So we will see this smaller nucleus splitting
into two lobe like things. Larger nucleus would disintegrate,
So this is all disappeared. And only the lower half of the body or the
lower half of the cell has gullet. That means the food can enter only through
here. But if it divides into two,
The upper part should also have a structure from where it can take food in. So here the upper half or upper part also
develops a gullet, The lower part anyways has its gullet
here. So now the nucleus has undergone splitting
the micro nucleus and the upper and the lower part they have their individual gullets. The constriction is going to take place from
here. It is a transverse plane. So now in the next stage both these halfs
they have their smaller nuclei, Larger nucleus is not yet formed again,
Both have their gullets. And the constriction is going to get deeper
from here. And finally these two will separate into two
daughter cells. They will develop their macro nucleus all
other organelle and attain the shape of the parent cell. They will grow in size and become exactly like
parents, The plane of division is transverse, so it
is also called transverse binary fission. In all three whether it is irregular longitudinal
or transverse one parent cell is dividing into daughter cells. So that is why we call them immortal. Because there is no natural death. Every time a cell is formed it is going to
give rise to two daughter cells. Now this is fission the binary one. Let us talk about multiple fission. Here every parent cell is dividing only into
two daughter cells. If one parent cell is producing many daughter
cells. Then by splitting obviously then it will be
called multiple fission. So let us take multiple fission now. So after binary fission, let us talk about
multiple fission. And after this we will talk about a slightly
different version of binary fission. What happens in multiple fission,
One parent cell undergoes fission or splitting to form
many daughter cells. And that is why the term multiple fission. It is seen in plasmodium, the malarial parasite,
amoeba During unfavorable condition. So amoeba show this but normally in favorable
condition it will show binary fission, But the condition are unfavorable then it
will show multiple fission also. Now what happens in this the parent cell during,
or if you are talking the example of amoeba or plasmodium the parent cell first undergoes nuclear
division, So it is a uni-nucleate cell first its nucleus
would divide multiple times. Multiple nuclei are formed. So only nuclear division is taking place right now That is karyokinesis. Each nucleus gets surrounded by little cytoplasm
and a membrane. So each nucleus is getting its own cytoplasm
and a plasma membrane. After this the parent cell ruptures. When parent cell ruptures these multiple cells
or daughter cells are released. So one parent cell is giving rise to many
daughter cells. This is multiple fission. In case of amoeba what happens is,
During unfavorable condition in amoeba during unfavorable conditions, it withdraws its pseudopodia becomes circular and secrets a thick layer around it. This layer is known as cyst. And this process is known as encystment. It remains in this condition throughout the
unfavorable condition. So this is during unfavorable conditions. So during that time it secretes a thick cyst
around itself it become circular by ansorbing or withdrawing all the pseudopodia. And it has its nucleus as it is, nothing takes
place during this time. so it remains in this cyst form. When the favorable condition approach. When the condition gets normal then the cyst
is lost. It loses its cyst, its nucleus undergoes division
so it would have many nuclei. All these nuclei will get surrounded by some
cytoplasm and the plasma membrane. That means daughter cells are formed here. And after this the parent cell will rupture
releasing all these daughter cells. So here one parent cell is giving rise to
many daughter cells. It can happen with encystment stage also,
It could happen straight away. Like it happens in plasmodium. Now there are some organisms like opalina
and paelomyxa, They shows something combination of binary
fission and multiple fission. The parent cell that is opalina and paelomyxa
which are protozoans. They are multinucleate,
Normally the cells are multinucleate in all other fission which we talked off,
The cell was uni-nucleate. Whether it was binary fission or even multiple
fission. These organisms are normally only multinucleate. So normal condition is multiple nuclei. Now what happens is this parent cell. Undergoes binary fission so when it shows
constriction in the cytoplasm. The nuclei get divided into two groups. One group goes into two daughter cell other
group goes into other daughter cells. After this there would be two daughter cells
formed. Let us just you know count these numbers of
nuclei, 123456789 and let us say 10. Now when the splitting takes place the distribution
of nuclei is not always 50 – 50. So it is 123456 here are four here. So the two daughter cells which are formed
they would have unequal number of nuclei. But it is not same as the parent cell. What has happened? First cytokinesis,
In all other divisions we talked of nuclear division first. First followed by cytoplasmic division,
In this case cytoplasm divides. Now in both these cells nuclear divisions would
takes place and they would regain their parent cell size and same number 10 or nuclei in
this case, And same here 456789 and 10. So the basic difference here also it is fission. It is binary fission only. But the difference is in all other fission
that we talked of Binary, regular, longitudinal, transverse
and even multiple. It is nuclear division first followed by cytoplasmic
division. In opalina and peolmyxa it is binary fission. One parent cell is giving rise to only two
daughter cells. But it is nuclear division or karyokinesis
first followed by cytokinesis. So this is how these two organisms are different. So though binary fission but in a different
manner. It is this division also known as plasmotomy. So slightly different type of division that
is seen in two organisms. So with this we are done with fission. Now let us talk about which is another method
of asexual reproduction. So next method is budding. Two types buds are seen in organism some buds
which are seen outside the parent body called exogenous buds and the ones which grows inside
the parent body are endogenous. Exogenous budding is what we have seen in
junior classes also. Example is Hydra, we also see it in east. In east the parent body shows a tiny out growth
which is known as a bud. This grows to a certain size and when it attains
a size and structure that it is capable of surviving on its own,
Then it pinches off from the parent body and then it would attach somewhere or free – floating,
In case of hydra this is east, in hydra the body is long, cylinder and vast like,
And they are attached to substratum. They have these tentacles again from the body
an outgrowth is seen. the outgrowth is a tiny bud projection kind
of a thing. Later on this will, initially it is going
to be just a projection then after it attains a size it starts looking like the parent in
every respect but for the size. So this tiny bud is know going to look like
the parent, it has its tentacles and everything. So it’s the baby hydra which is growing on
the parent body. Once it becomes like of a size where it can
survive on its own it will detach and this tiny structure will anchor on some substratum
and will grow into an adult. We have seen these projections these growths
outside the parent bodies, So we are calling them exogenous buds. Endogenous buds are inside. So we don’t see it from outside unless and
until they come out. The organism where we see this endogenous
buds, One is a sponge that is spongilla,
Spongilla is the only freshwater sponge. And it produces endogenous buds. So if the body of the sponge has these Austia
for inlet of water and the Asculum for the outlet,
The buds would grow inside here. So you would not see it from outside till
the buds come out. These buds are known as gemmules. These endogenous buds are called gemmules. Now let us see the structure of these gemmules. In the central part they have cells which
are basically stem cells. They will give rise to the complete organisms. These cells are called Archaeocytes,
These cells, each cell is capable of giving rise to an individual. So Archaeocytes they are basically stem cells. This complete structure is surrounded by a
thick jelly like mucilaginous substance, The basic purpose of this is to protect these
cells from injury or desiccation. At one end there is an opening. This opening is known as micropyle. And this layer is mucilaginous. In this musilaginous layer are present speicules. The spicules are needle like structure. They are of the same diameter in the middle. And their ends are pointy like needles. These spicules are known as mono-exonic spicules. So here in this mucilaginous layer there are
these spicules. These spicules are meant for protection. These are pointy structure needle like hard. These spicules can be made up of silica or
calcium salts. These are mono-exonic spicules. They can be made up of silica or calcium salts,
Especially calcium carbonate. Now when these gemmules or endogenous buds
are completely formed. They are released. So they come out of the Asculum the upper
opening. When they come out, they remain in water. Free floating structures. Whenever they come in contact with a suitable
substratum, Because sponges are also attached to the substratum. So whenever they come and contact with the
suitable substratum, They will attach there with their micropyle
at the lower end. So the attachment would be such that the micropyle
is here, the cells , the archaeocytes and the mucilaginous layer around it. And these archaeocytes will come out of this
micropyle to form the sponge body. So the attachment is always through micropyle
end. The spicules and everything then the mucilaginous
layers and everything will degenerate so the buds, but they are inside the body called
gemmules. The examples where we see these gemmules spongilla. It’s a sponge. The only freshwater sponge. All other sponge is of marine. So this the structure of gemmules. They are endogenous. So exogenous outside the body, which can be
seen in the form of small outgrowths. Endogenus buds are inside the parents bodies. At a given time there can be many gemmules
which are growing in a body. And then all those when they are formed, they
are released from the parent body. So two types of buds,
So second method of asexual reproduction budding is done. Now let us take the next method of asexual
reproduction.

100 thoughts on “REPRODUCTION IN ORGANISMS -01 For Class 12th and AIPMT

  1. Very impressive explanation given by the teacher in this video , must watch this video to increase the basic knowledge about the topic .

  2. πŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ‘ŒπŸ™πŸΌπŸ™πŸΌπŸ™πŸΌπŸ™πŸΌπŸ™πŸΌπŸ™πŸΌπŸ™πŸΌ

  3. Mam i didnt understand spongilla endogenesis part especially about the 2nd stage of division of spongilla can u please tell me abt it clearly

Leave a Reply

Your email address will not be published. Required fields are marked *

Back To Top