BIOLOGY CHAPTER 01 REPRODUCTION IN ORGANISM CLASS 12

CHAPTER 01 REPRODUCTION IN ORGANISM

Hi,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 tonew 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 continuityof 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 wedivide or classify the reproduction. Asexual Reproduction and Sexual Reproduction. Asexual Reproduction is involvement of oneparent. So it is also known as uni -parental,Whereas in sexual reproduction two parents a male and a female are required so it isalso known as bi-paternal. In asexual reproduction formation and fusionof 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 processof meiosis. And in meiosis genetic variation takes placedue to crossing over.

Whereas in this case as no gamete are fusingso no variation is there. So the offsprings which are there,They are identical to the parents. So the offsprings are same as parents orthat 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 combinationalso possible 50 - 50, 60 - 40 or even variable. So genetic variation and the offsprings aredifferent, 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 reproductionand the methods by which this takes place. Asexual reproduction takes place by variousmethods. So let us first write down the names and thentake these one by one. One is fission, these fission basically isthe parent cell splits into daughter cells. It can be binary fission that means one parentcell splits into two daughter cells. Or it could be multiple fission. Another method of asexual reproduction isby budding, The buds normally are termed as an outgrowthon the parent body, So most of the times which we talk of arethe buds which are outside these buds are known as exogenous. So there are two types of buds which are seenone 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 justundergoes fragmentation breaks up into different fragments and each fragment gives rise toan individual, Then spore formation there are various typesof spores, Like zoospores, conidia, oidia and all thosethings.

 And one more when some vegetative part ofthe 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 vegetativepropagation and artificially how we can help these plants propagate or we can use thismethods for propagation of the plants. So these are the categories in which we dividethe 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 couldbe unicellular organism splits into daughter cells.

So one parent cell splits into two daughtercells. Splitting is going to beFirst 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 binaryfission, Like irregular binary fission,Irregular binary fission, irregular means there is no fixed plane in which the nucleusor the cytoplasm is going to split. This is seen in Amoeba. In amoeba the cytoplasmic constriction takesplace or can take place in any plane. So if this amoeba has to divide or reproducefirst its nucleus will start to show constriction.

Then this nucleus would completely divideinto two nuclei and cytoplasm also starts showing constrictions. And now these two daughter amoebi with theirnuclei are formed. In this case we have seen the constrictionslike this. But because of the shape of amoeba is notfixed, It can show constriction in any plane,It can show constriction from side, from top, anywhereAnd that is why we are calling it irregular binary fission. What has happened to the parent cell? The parent cell undergoes fission to producetwo daughter cells. Technically speaking this cell has now dividedinto 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 fissionthey are considered as immortal. Immortal because normally what happens isreproduction 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 willdivide by binary fission. Again two daughter cells will be formed. So naturally they do not undergo deathAnd 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 cells will divide into two but the planes of the divisions is decided. It is longitudinal,So longitudinal binary fission. That means it is going to be vertical typeof fission. It is seen in euglena. Euglena is a flagellate. It has one large flagellum and there is onemore 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 thegullet, Euglena is an organism which is placed betweenanimals and plants. It has plant like characters,That means it has chloroplast it can perform photosynthesis. Animal like character is, it is without cellwall. Animal cells don't have cell wall. So, this has one characteristics of plantand one characteristics of animal. So if it has sufficient light available toit, it will perform photosynthesis. But if light is not available then it takesfood 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 gulletend divides. So here we start seeing an organism with twogullets formed , The upper end there are two such structuresand the lower part of the body or cell is still fused. So the splitting of cytoplasm or the constrictionis 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 wouldget two daughter euglena and now they will develop their flagella.

Splitting or the plane of splitting is longitudinalor vertical. Again one parent cell is giving rise to twodaughter cell. So that is why it is also binary fission. Because of the plane it is called longitudinalbinary fission. The third type the plane is transverse, soit 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 slipperlike 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 anda smaller micro nucleus. The macro nucleus is responsible for all activitiesfor 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 thissmaller nucleus will split, So we will see this smaller nucleus splittinginto two lobe like things. Larger nucleus would disintegrate,So this is all disappeared. And only the lower half of the body or thelower half of the cell has gullet.

That means the food can enter only throughhere. 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 alsodevelops a gullet, The lower part anyways has its gullethere. So now the nucleus has undergone splittingthe micro nucleus and the upper and the lower part they have their individual gullets. The constriction is going to take place fromhere. It is a transverse plane. So now in the next stage both these halfsthey have their smaller nuclei, Larger nucleus is not yet formed again,Both have their gullets.

And the constriction is going to get deeperfrom here. And finally these two will separate into twodaughter cells. They will develop their macro nucleus allother organelle and attain the shape of the parent cell. They will grow in size and become exactly likeparents, The plane of division is transverse, so itis also called transverse binary fission. In all three whether it is irregular longitudinalor 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 togive 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 intotwo daughter cells. If one parent cell is producing many daughtercells. Then by splitting obviously then it will becalled multiple fission. So let us take multiple fission now.

So after binary fission, let us talk aboutmultiple fission. And after this we will talk about a slightlydifferent 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 favorablecondition it will show binary fission, But the condition are unfavorable then itwill 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 nucleardivision, So it is a uni-nucleate cell first its nucleuswould 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 cytoplasmand a membrane. So each nucleus is getting its own cytoplasmand a plasma membrane. After this the parent cell ruptures. When parent cell ruptures these multiple cellsor daughter cells are released. So one parent cell is giving rise to manydaughter 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 theunfavorable condition. So this is during unfavorable conditions. So during that time it secretes a thick cystaround itself it become circular by ansorbing or withdrawing all the pseudopodia. And it has its nucleus as it is, nothing takesplace during this time. so it remains in this cyst form. When the favorable condition approach. When the condition gets normal then the cystis lost. It loses its cyst, its nucleus undergoes divisionso it would have many nuclei. All these nuclei will get surrounded by somecytoplasm and the plasma membrane. That means daughter cells are formed here. And after this the parent cell will rupturereleasing all these daughter cells.

So here one parent cell is giving rise tomany 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 opalinaand paelomyxa, They shows something combination of binaryfission and multiple fission. The parent cell that is opalina and paelomyxawhich 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 multiplefission. 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 showsconstriction in the cytoplasm. The nuclei get divided into two groups. One group goes into two daughter cell othergroup goes into other daughter cells.

After this there would be two daughter cellsformed. Let us just you know count these numbers ofnuclei, 123456789 and let us say 10. Now when the splitting takes place the distributionof nuclei is not always 50 - 50. So it is 123456 here are four here. So the two daughter cells which are formedthey 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 wouldtakes place and they would regain their parent cell size and same number 10 or nuclei inthis 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 fissionthat we talked of Binary, regular, longitudinal, transverseand even multiple.

It is nuclear division first followed by cytoplasmicdivision. In opalina and peolmyxa it is binary fission. One parent cell is giving rise to only twodaughter cells. But it is nuclear division or karyokinesisfirst followed by cytokinesis. So this is how these two organisms are different. So though binary fission but in a differentmanner. It is this division also known as plasmotomy. So slightly different type of division thatis seen in two organisms. So with this we are done with fission. Now let us talk about which is another methodof asexual reproduction. So next method is budding. Two types buds are seen in organism some budswhich are seen outside the parent body called exogenous buds and the ones which grows insidethe parent body are endogenous. Exogenous budding is what we have seen injunior classes also. Example is Hydra, we also see it in east. In east the parent body shows a tiny out growthwhich is known as a bud. This grows to a certain size and when it attainsa 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 bodyan outgrowth is seen. the outgrowth is a tiny bud projection kindof a thing. Later on this will, initially it is goingto be just a projection then after it attains a size it starts looking like the parent inevery respect but for the size. So this tiny bud is know going to look likethe parent, it has its tentacles and everything.

So it's the baby hydra which is growing onthe parent body. Once it becomes like of a size where it cansurvive on its own it will detach and this tiny structure will anchor on some substratumand will grow into an adult. We have seen these projections these growthsoutside the parent bodies, So we are calling them exogenous buds. Endogenous buds are inside. So we don't see it from outside unless anduntil they come out. The organism where we see this endogenousbuds, 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 Austiafor inlet of water and the Asculum for the outlet,The buds would grow inside here. So you would not see it from outside tillthe 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 whichare 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 athick jelly like mucilaginous substance, The basic purpose of this is to protect thesecells 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 arethese spicules.

 These spicules are meant for protection. These are pointy structure needle like hard. These spicules can be made up of silica orcalcium 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 budsare completely formed. They are released. So they come out of the Asculum the upperopening. When they come out, they remain in water. Free floating structures. Whenever they come in contact with a suitablesubstratum, Because sponges are also attached to the substratum.

So whenever they come and contact with thesuitable substratum, They will attach there with their micropyleat the lower end. So the attachment would be such that the micropyleis here, the cells , the archaeocytes and the mucilaginous layer around it. And these archaeocytes will come out of thismicropyle to form the sponge body. So the attachment is always through micropyleend. The spicules and everything then the mucilaginouslayers and everything will degenerate so the buds, but they are inside the body calledgemmules. 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 beseen in the form of small outgrowths. Endogenus buds are inside the parents bodies. At a given time there can be many gemmuleswhich are growing in a body. And then all those when they are formed, theyare 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 asexualreproduction.

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