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0:00 in our previous videos we discussed about the female reproductive part of a flower and we saw in detail the structure of the ovule which is also called the megasporangium and the structure is this one now this mega sporangium or the ovule is the place where the mega spores will develop and mega spores means the female spores now in this video we are going to talk about how that mega spore develop inside this mega sporangium or inside this ovule and the entire process of formation of megaspore in the ovule is called megasporogenesis here megaspore means the female spore and just call mega because it is
0:46 comparatively bigger to the male spores which are called microspores and genesis means formation formation we are going to talk about how female spores are formed inside the ovule okay so let's begin let's bring in focus only the ovule here you go now inside the ovule as you can see there is a mass of cell which is called the new cellulose now one lucky cell from this new cellus will grow in mass and it will become the mother cell to give rise to mega spores now which one will be that lucky cell well it is seen that one cell from the hypodermal region
1:31 near the micropile area will give rise to megaspores now you might think that hey i understood what is micropile area it must be somewhere here but what is hypodermal region well uh the cell the layer of cell which is outside the new cellulose or i should say the outer layer of cell in the new cellulose is called the epidermal layer of cells or the dermal layer of cells and the cell layer which is underneath it is called the hypodermal cell so this one will be the hypo dermal cell layer so one cell from the hypodermal
2:16 cell layer near the micropile area will increase in size and will give rise to mega spore later so let's say this is that lucky cell that has increased in size and has accumulated a lot of cytoplasm and will give rise to megaspore but mind you this is not megaspore yet this is just an ordinary cell that has increased in mass has accumulated a lot of cytoplasm but this is not a mega spore yet it will undergo a number of cell division to give rise to megaspore and we will see how but as this cell will now be responsible to give rise to megaspore we call this cell the megaspore mother cell quite makes sense right megaspore mother cell or we call
3:02 it mmc all right having said that having talked about mmc now let's focus on the cells that are surrounding the mmc because nucleus is made up of a number of cells on and only one got lucky to become the mmc what is the role of the other cells well the other cells will provide nourishment as the mmc grows in size it will derive the nourishment and it will derive the cytoplasmic content from the cells that is surrounding it all right now this mmc will undergo cell division but not any cell division it will undergo a special kind of cell division which is called meiosis or the reduction division in which the chromosome number of this mmc will get reduced to half in
3:49 each cell so if we say this is how it got divided into two cells so this is meiosis and if we consider that this cell has twice n number of chromosomes then after meiosis or i should say meiosis one because meiosis takes place in two stages so after meiosis one each cell will have half the number of chromosomes so they will have n number of chromosomes each now meiosis you may already know gets completed in two stages so after meiosis 1 takes place meiosis 2 which is similar to mitosis
4:38 and after meiosis 2 we get 4 cells and here the number of chromosomes stays the same number of chromosomes would be n in each cell so we saw that meiosis took place in the mmc and by the end of meiosis we got four cells that are haploid all right now can you tell me why mmc underwent meiosis and not any other type of cell division how about you pause the video for a while and think about it all right let me tell you the answer for any plant on earth when it undergoes uh the process of sporogenesis or gametogenesis where spores or gametes are produced let's say male and female gametes are produced
5:26 there meiosis takes place so that the chromosome number is reduced to half and later when the fusion of the male and female gametes take place they will give rise to a diploid organism or in this case a deployed plant which is having the same number of chromosomes as data of the parent plant simple right so this is the reason we see meiosis in megaspore mother cell and we saw that the megaspore mother cell gave rise to four spores at the end but now we will see that something happens to this four spores something very unusual happens here this three spores will degenerate
6:12 it will degenerate or i like to call it as sacrifice their lives so that one's poor can have a healthy and a fully nourished life so this three cells give up all its nourishment to just one cell which is the functional mega spore so this one here is finally a mega spore so this is a mega spore and it is haploid and also since only one spore later gave rise to an embryo sac this entire process of formation of the megaspore is called monosporic development
7:00 well now that we have got a functional megaspore how about we compare the process of megasporogenesis with microsporogenesis that is the formation of male spores but this will only make sense if you have watched a video of microsporogenesis already so if you have not watched i would recommend you to go back and watch that video first and then come back to this comparison part and for those of you who have already watched that video let's continue so uh in microsporogenesis we saw that there are number of cells inside the tibetan layer that are capable of giving rise to microspores now in case of female spore formation we saw all these new cellular cells are capable of giving
7:46 rise to megaspore but just one cell becomes the megaspore mother cell but when it comes to microsporogenesis all the cells that are capable of formation of microspore microspore mother cell actually forms microspore mother cell so here if we count we'll see that we have eight cells uh inside the tip atom and all these eight cells will simultaneously undergo meiosis and will give rise to uh eight multiplied by four we get 32 microspores and the interesting part is that all these 32 microspores they remain functional unlike in
8:32 megasporogenesis where only one megaspore at the end remains functional so the number of male spores is always higher than a number of females poor and the reason is a male spore has to travel all the way from the anther to the stigma and sometimes to the stigma of some other flower in some other plant in the nearby plant of the same species so while doing so while traveling from from the nth or to other parts a number of male spores gets destroyed it may fall on wrong places or it may not develop pollen tube so a number of things might happen and that is the reason the number of male spores is always higher
9:17 and on the other hand there is no such risk involved when it comes to a mega spore because all all it has to do is to sit in a bucket of new cellular cells and wait for the pollen tube to reach it right reach the mega spore and fertilize it and that is the reason just one single healthy fully nourished megaspore is sufficient and hence we get just one functional megaspore in an ovule all right now that we have learned all about megaspore and how it is produced how about we try and answer a question related to it so what i would like you to do is to pause the video and try and answer these questions okay i think you have found the answer to all these questions but let me tell
10:04 you how i find out the answers so the first question is if a megaspore mother cell has 20 chromosomes that means this cell here if it has 20 chromosomes how many functional megaspore will it produce well we have seen one megaspore mother cell by the end of meiosis produces four megaspores out of which just one stays functional so this one here is the functional [Music] megaspore right so uh the first question how many functional megaspore will it produce the answer would be one it produces just one functional megaspore and the next question is what
10:52 will be the number of chromosomes in it well the number of chromosomes in the functional megaspore is half the number of chromosomes that was in the megaspore mother cell so in the question it said that the megaspore mother cell has 20 chromosomes so half of it that means the functional megaspore will have 10 chromosomes so this was all about how omega spore is formed inside the ovule in an ovary in our future video we will talk about how this mega spore further divides and give rise to female gametes
