 In our previous videos, we have discussed so much about reproduction in flowering plants. We have discussed in detail about how the male gametes are formed and how the female gametes are formed. And in this video, we are going to talk about how both these gametes fuse, how the fertilization actually takes place. So for that, we have taken a beautiful bisexual flower here. That means it has both the female and the male parts in it. And also, most importantly, this flower is self-pollinating. Which means the male gamete of this flower has the capacity to fuse or fertilize the female gamete of the same flower. Alright, having said that, let's begin the story of fertilization. So it begins with the release of pollen from the antholobes. The small particles that you see here are pollen grains. Next, this pollen grains fall onto the female part of the flower. It can happen through wind, it can happen through other pollinating agents like bees or other insects. So here, let me be that pollinating agent. I will carry the pollen all the way to the female reproductive part here. This yellow pollen grain actually acts like a bag that holds the male gametes. Now, can you recall how many male gametes a pollen grain contains? Well, each pollen grain will have two male gametes and both the male gametes will be haploid. Alright, now let's talk about the female gametes. Where are they? Well, the female gametes lie somewhere in this small, small lobe-like structures that you see in the ovary. They remain hidden somewhere in these ovules. Each ovule contains one female gamete or we can say a single embryo sac. So this male gamete that has come all the way from the anther to the stigma has to do some more traveling. It has to travel all the way down the style to finally reach the ovule. And they do this with the help of something called the pollen tube. The pollen tube helps the male gametes to reach the destination. And this is where the fusion or the fertilization takes place. Now, how about we zoom into this path, the ovule and the tip of the pollen tube to have a clear picture. Have you noticed something new? Well, this green color lobe-like structure here seems new, right? Well, this is our female gametophyte or the embryo sac that contains the female gamete. And this was not visible in this tiny picture here. How about we enlarge it even farther? Let's enlarge the female gametophyte. Now, take a moment to look at the structure of this embryo sac. You will see that it has one large cell and few small cells. So let's begin with these three cells here. These three cells here are called antiportal cells. Now, the role of these antiportal cells in fertilization is not known. Some research shows that this persists all throughout fertilization and some also believes that it disintegrates. So like in most common textbooks, let's consider that it disintegrates. So now we have three cells on top and two nuclei at the center of this large cell. And we will start with these two cells on top. These two cells are called the synergies. Without them, the pollen tube won't even reach the embryo sac. The pollen tube gets the direction with the help of these pink structures that you see, the finger-like projections. These are called filiform structures. And they actually show the pollen tube, the path through which they have to enter. So let's bring in the pollen tube now. This is the pollen tube here. And these are the two male gametes that it brings with it. So as soon as the pollen tube reaches the synergies, one of the synergies actually makes path for the pollen tube to enter. It disintegrates and slowly these male gametes, it starts entering the synergies cell. So one by one, both these male gametes will enter the synergies cell. And slowly we will see that both the synergies, after they have done their work, it will disintegrate. It will disappear because their job is done. Now we are left with the egg cell that is the female gamete. And then we have two nucleus in the center. These two nucleus are called polar nuclei. Now let's talk about the ploidy of this embryo sac. What do you think it will be? Well it is seen that every nuclei that we just discussed or every cell that we saw inside this embryo sac were all haploid. So this egg cell nucleus is haploid. And this two polar nuclei here are also haploid. Now if you have no clue about how they became haploid, then I would recommend you to go back and watch the video of mega sporogenesis where we discussed how and at which point during the development meiosis took place and all these cells became haploid. Alright, moving ahead let's talk about this pollen tube now. After the release of the male gametes, this pollen tube has no role to play and therefore it also disintegrates and disappears. Now all we are left with are these polar nuclei, this egg cell here and these two male gametes. Now this is the most important part of the entire story. One of the male nuclei moves towards the egg cell and fuses with the egg cell. This process is called fertilization or syngamy where the male gamete and the female gamete fuses and they fuse to give rise to a diploid cycle. We saw that male gamete and female gamete both haploid fused therefore this zygote will be a diploid one. And this zygote later forms an embryo and that embryo gives rise to a baby plant. Wonderful. Then what is the role of this three nuclei that's just lying there? Well, the other male gamete, this one, will slowly come and fuse with a polar nuclei and they together form something called the primary endosperm nucleus. This is nothing but a nutritive tissue that provides nourishment as the zygote develops. So what do you think should develop first, the zygote or the primary endosperm nucleus? Well, the primary endosperm nucleus develops first because without food, without nourishment how will the zygote even develop, right? Now, can you tell me what will be the ploidy of this primary endosperm nucleus? It had two haploid female nuclei and one male gamete nuclei, right? So the ploidy will be 3n or triploid and also since three different nuclei fuse together to give rise to this triploid structure, we call it triple fusion, the fusion of three nuclei. And also since the male gamete fused twice, once to form the zygote and next to form the primary endosperm nucleus, this entire process is called double fertilization, which is typical for an angiospermic plant. Alright, now that we have seen how fusions of male and female gametes takes place, we know what is double fertilization and triple fusion, how about we try and solve a question related to it. So the question is, if each haploid nucleus in an embryosac contains 10 chromosomes, so this is an embryosac and every nucleus has 10 chromosomes, then at the end of double fertilization, how many chromosomes will the primary endosperm nucleus have? So this is the primary endosperm nucleus. What do you think? How many chromosomes will primary endosperm nucleus have at the end of double fertilization? Pause the video for a while and try to find out the answer. Alright, so the question is asking about the number of chromosomes in the primary endosperm nucleus and we know that it is formed by the fusion of three nuclei of which two are female and one is a male nuclei, right? And the haploid female nuclei of the embryosac has 10 chromosomes, which is mentioned in the question. So every female nuclei will have 10 chromosomes each and what will be the number of chromosomes of the male nucleus? Well, the male gamete or the male nucleus here also comes from the same species, right? Therefore, its haploid number of chromosomes would be same as that of the female chromosome. Therefore, it will also have 10 chromosomes in its haploid nucleus. So here is the answer. The primary endosperm nucleus which has three haploid nucleus will have a total of 30 chromosomes.