 Polynesian is the act of transferring the pollen grains on to the stigma. Great! We have transferred pollen grains on to the stigma. But what happens next? That's basically what we want to talk about in this video. In this video we're going to see exactly how the sperm cells are going to reach the eggs and eventually how a new baby plant is born. So let's zoom in on this female part and see what happens after pollination. So here is the pollen grain which has landed on the stigma. Now a couple of things is first of all there'll be a lot of pollen grains and pollen grains are usually much smaller than what I've shown over here. But I've shown them big and I've shown one so that we can clearly focus on and see what's going on. So the sperm cells are going to be produced inside this pollen grains and the egg cells will be formed inside the ovules over here. So we need to get the sperms from here to there. But how does it happen? It is for this reason the pollen grain starts germinating. So what's going to happen is the pollen grain starts absorbing some of the secretions that are done by the stigma, the sticky stigma, and then the pollen grain starts germinating and a tube starts growing from this grain. So let me show you. So a tube starts growing from this pollen grain and the tube will eventually, the tube will eventually go all the way into the ovary. This is the ovary. It'll go all the way into the ovary and all the way into the ovule. So it makes a path for the sperms and leads them all the way to the ovule where the egg cells are lying. Now at first you may be wondering, well how does a pollen tube know exactly where the ovules are? Well it turns out that the ovules over here start secreting some chemicals and the pollen tube basically senses the chemicals and starts growing towards it. Now we've talked about such motion before. We call this the chemitropism. Tropism means movement and chemi means movement due to chemicals. Anyways, don't worry too much about that. A pollen tube has now grown and now we will see some sperm cells which I'm drawing over here. Let me draw that over here. A couple of sperm cells, they will start moving through the pollen tube and they will enter into the ovule. Great. What's going to happen next? Well let's zoom in on this ovule and find out. So here is a zoomed in version of that ovule. This is that same pollen tube and this is that ovule. A single ovule have zoomed in over here. Now if you look inside the ovule you'll find the egg cell. That's where the sperms need to reach. But here's the thing. The ovule doesn't only contain egg cells, it also contains some other cells as well. In fact if you count it turns out there are one, two, three, four, five, six and this whole big total seven cells. This big cell has two nuclei inside of it. All right? So it turns out there are total eight nuclei inside this ovule. But don't worry about it. We don't have to worry too much about it right now. So let's not worry about these other cells. And so now from this pollen tube the sperms are coming in. So let me just draw those sperm cells. So these are the nuclei of the sperms. They will move, they'll move and eventually the pollen tube guides them into the ovule. Now what happens? Well one of the sperm will unite with the egg cell. So one of the sperms unites with the egg cells and the other sperm, not this one, the other sperm cell will go and unite with the two nuclei. Remember I showed that there are two nuclei over here sharing one entire cytoplasm? So that other cell, other sperm is going to unite with that. Now the reason why I'm telling you this, even though that's not really important, the reason I'm telling you this is because there are two sperms uniting. One uniting with the egg and one uniting with the other cells. We say there are two fertilizations happening in this plant. And that's why usually in flowering plants we say double fertilization takes place. Fertilization is basically the uniting of the sperm cells with one of these cells. But anyways we don't have to worry about that other sperm and that other thing. So let's get rid of that. We will only consider the fusion of the sperm cell with the egg cell. So when that fusion happens we now get a new cell. And this new cell, which is basically the fusion of the two, we give a name to that. We call this the zygote. Zygote. So what exactly is zygote? Zygote is the fusion of sperm, sperm and the egg. Great, we now have a zygote. What happens next? Well next a lot of changes start happening. First of all the pollen tube has done its job so it'll start disintegrating. Then we will see that the zygote will start dividing from 1 to 2, 2 to 4, 4 to many. So let me show you that. So here it is. We can now see the zygote is multiplying. It's going into dividing into many many many more cells. And eventually you will find that the zygote would eventually have divided into a lot many cells to give us this kind of structure. This structure is now ready to grow a future baby plant. So this now is called, let me write that down, this structure is now called the embryo. So you can think of embryo as the future, future plant. It's going to grow into the future plant. In fact we can actually identify the parts of the embryo. If you look at these two leaf-like structures, they are called the cotyledons. Let me just write that down. So these two leaf-like structures are called the cotyledons. And their main job is to provide the embryo with all the nutrition, all the food that they need once it starts growing. It will require a lot of food. And remember we don't have leaves yet. So until the new leaves get formed, the cotyledons are the one that's going to provide them with nourishment when it starts growing eventually. We'll look at that in a second. And then you can see this part over here. This and important to see them. And of course over here I have drawn two cotyledons. But not all plants will have two cotyledons. Some will have two which is called dicots. And some plants will have just one cotyledon. We call them as monocots. You may have learned about that previously. Anyways this part as you can see in between the two cotyledons, this is the part that eventually in the future will grow into a new shoot. And that part is called the plumeule. Plumeule. This will grow into a new shoot. And finally this part over here. Let me write that in a different color. This part. This is something that will eventually come out from here and grow into a new root. So this is called the radical. So the radical grows into a new root. The plumeule grows into a new shoot. And the cotyledons kind of act like leaves. They're not really leaves, but they act like leaves in the sense they give them all the nourishment needed once it starts growing. And a lot of other changes happen as well. For example, the outer wall starts to become a little hard. And now we no longer have an ovule, we are going to call this as a seed. So the fertilized ovule has now finally got converted into a seed. Great. But what happens to the flower? Well, let's see. So here is the flower. Here is our flower. We are zooming back out now. All right. Here is the flower. Here is that particular ovule we're talking about. What are the changes that are happening? First of all, we will see now a lot of ovules would have gotten fertilized. Remember, I just showed one pollen grain, but there are multiple pollen grains, which are going to fertilize multiple ovules. So all these ovules have now gotten converted into seeds. They're now seeds. And the unfertilized ones are eventually going to disintegrate. What else is going to happen? Well, we no longer need the stamens. So that stamens will start drying off. We no longer need the petals. So that you will see the petals fall off. And we will now find eventually the ovary. This ovary starts swelling and starts becoming bigger and bigger. Here it is. The ovary starts becoming big and big. And eventually it's the ovary that's going to grow into a fruit. And there will be seeds inside that particular fruit. So over here, I've shown a tomato as an example, but it can be any fruit with seeds in them. Then you can eat that fruit and then sow the seeds. So maybe you can't do that for tomato, but for some other fruit, you may be able to sow the seeds. So next question is what happens once you sow the seeds? Well, once you start sowing the seeds, you will now see that first root starts developing from the radical. Radical is the part where the root develops, right? Then we will find the shoot starts developing from the plumeule. Remember, we just talked about that. Let me show you that. So from the radical, the roots are coming from the plumeule, the shoot is coming. And the cotyledons, these cotyledons, these two things are the cotyledons. The cotyledons become massive. They become the swell up and they almost take up the entire seed. These are now the cotyledons. It's the cotyledons that are providing them with all the nourishment needed to grow. They're giving them all the food to grow. And then as time passes by, we will now find that eventually that shoot starts growing into new leaves. And now the leaves, the first leaves can now, true leaves we call them, can now start photosynthesizing and start and can start making the new food. And now no longer cotyledons are needed. So the cotyledons eventually get drained. They will now start shrinking. And eventually the cotyledons go away. They'll shrink. And finally, a new baby plant is born. The roots can keep on growing. The plant can keep on growing. And once the plant becomes mature enough, the plants can grow new flowers. The flowers can get pollinated. And now the cycle can repeat. This process of new plants growing from a seed, by the way, is what we call germination. And so this in short explains how fertilization happens in plants. So to quickly summarize the important points, after pollination, a pollen tube starts growing and it directs the sperm cells all the way into the ovule. Once the sperm cells reach the ovule, one of the sperm fuses with the XL. This process of fusion is what we call fertilization. And the new fused cell is what we call a zygote. The zygote can now multiply, divide into many cells and eventually forms what we call the embryo. The embryo is the future plant. The cotyledons of the embryo are going to nourish it once the embryo starts, once the seed starts germinating. The radical is where the root grows and the plumeule is where the shoot starts growing. At the same time, the flower loses all its other parts, ovaries swells and becomes the fruit. And eventually as the plant grows, the cotyledons shrink and now the fleas take care of all the nourishment and the food requirement of the plant.