Double Fertilization

by Jason Amores Sumpter
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pollen was a wonderful technological advancement in the evolutionary history of plants. Prior to pollen, plants had to use water to get the sperm to the egg. Pollen provided a knave anu, that allowed for a much more diverse variety of methods of connecting sperm and egg. Now pollen is the male gimme to fight, and it's surrounded by a water tight coating made of a material called Spore. A pollen in and it actually contains two cells, the generative cell and the tube cell. We'll talk about what those do momentarily now. Pollen forms when a micro sports micro sports site, which is a deployed cell, goes through, my oasis informs Micro spore, which is hap Lloyd and through the process of mitosis, will form micro comida fights. And you'll see in a little bit why I have a two right there. Because, as we'll see, there's actually going to be two microgram media fights or two sperm involved in angiosperms reproduction. Now the female component is the embryo sac. This is the female. Give me to fight, and it is contained within the AV you'll and it's what will develop into the embryo. It forms when a mega sports site. Deployed structure undergoes my ASUs two form mega spores and actually it's going to form four of them. Now three of these will degenerate. One will go on to form the mega Gumede a fight. And the reason I haven't ate right here is as you'll see, this mega gamy to fight is actually going to have eight nuclei in it. Two of these are going to be what are called the polar nuclei that are happily nuclei that are going to develop into endo sperm, which is something we'll talk about in just a second now. Pollination occurs when the pollen it, um, is transferred to the fuel. It begins with germination where pollen will land on the stigma, resume growth, usually by absorbing some water, and the tube cell in the pollen grain will generate a pollen tube. This pollen tube grows through the style and connects to the AV. You'll and it will transmit those male gametes or sperm. No, I said I'd get back to that to sperm thing, and here we are. The reason for it is something called double fertilization. So basically the pollen tube releases to sperm one is going to fertilize the egg and form the embryo. That's to be expected, right? The other does this funky thing. It interacts with those polar nuclei and will form endo sperm. And this Endo sperm is a nutrient rich material or tissue really that surrounds the embryo and provides it with things like starch, protein and oil. In fact, when you eat nuts, you're actually basically eating end of sperm. So, for example, if you've ever eaten a peanut, you might notice that on a peanut there's that little kind of nib thing on the end. Or if you crack the peanut in half, you'll see that there's like a little nub structure on one end that is, the embryo, actually the nut, most of what we're eating. What we think of as the nut is the end of sperm, and it's super nutrient rich, right and also delicious in many cases. Now, these two sperm not to get too sidetracked on endo sperm. But these two sperm, these two male Gumede a fights. I'm sorry. Male gametes will be produced by the generative cell, which divides by mitosis and produces those two sperm sends him down the pollen tube. No seeds will develop once the visual is fertilized and it contains the embryonic plant surrounded by a protective coat. It's also got some endo sperm in their right. Never forget the endo sperm. And just look at a nice overview of this process Here we have on one side our get my head out of the way. Here we have our, uh, micro sprang Geum producing micro spores. The micro sport will go through my oh, sis, right. That's what's going Oops, that's what's going on here. And then it will, uh, produce the micro me to fight through my toe, sis, because it has to make those to you. Sells the generative cell and the tube cell. And that is our microgram me to fight or pollen. So this whole thing right here is our pollen green. Now, on the female side here, you can see those four cells that we talked about, three of which are going to degenerate. And one is going to go on Thio, go through my ketosis and form those eight nuclei, right, And you can count them off in this image. It's a little small, but we have 123 on top, right here, these three guys, our polar nuclei. So that's four and five. And then, if you can see on the bottom here we have another three cells. So that's going to be 67 and eight so that that accounts for all of those eight nuclei. And that is all part of the mega Me to fight or the embryo sac. No, just to finish it off here, you can see the pollination happening. We have our pollen grain landing on the stigma, so that's a stigma. Remember, here's our little orange pollen grain. The tube cell is going to produce this pollen tube that goes down to the of you'll, and here you can see the pollen tube reaching the AV. You'll right, and it's going to send the sperm into theme. The AV you'll where they won, will interact with the egg cell right here, and one is going to interact with these polar nuclei to form the end of sperm. With that, let's turn the page