How does a little plant seed turn into a great big tree? Well, all great things have small beginnings, and plants are no exception. The development of a seed begins with fertilization. The pollen grain will deposit sperm into the ovule on the flower, And this results in embryogenesis, which is the, development of the seed and, more importantly, the plant embryo within seed. Now after fertilization, what you're left with is a zygote. And this zygote is going to divide into 2 daughter cells known as the apical cell and the basal cell. So here we have our zygote and it is going to divide into an apical cell and this basal cell. Now the apical cell is going to form a mass of cells that will eventually basically become the plant. This cell mass will differentiate into those primary meristems we talked about, the protoderm, ground meristem, and pro cambium. And you can see the apical cells, division as it continues along to this structure, and eventually just, you know, it's growing into this mass of cells, which will eventually form the plant embryo that, you can see behind my noodle here. Now the basal cell forms a structure called the suspensor that contributes to support structures for the embryo. Only one cell in the suspensor will actually contribute to the plant embryo. So here, we have our suspensor. Now these embryonic plants have embryonic leaves, we call them cotyledons, And plants will actually be differentiated into monocots and dicots depending on how many cotyledons they have. Monocots have 1 cotyledon. Right? Mono, meaning 1. And eudicots have 2 cotyledons, di meaning 2. And if you're curious the u part here is, means true, So these are it's saying basically, 2 true leaves or cotyledons. Now the embryonic plant has some other structures that we should go over. These include the hypocotyl, which you can see here, let me jump out of the way, that is basically the embryonic stem of the plant. So it's this portion here. It also will have a radical, which is an embryonic root. And here, you can see our radical. Now, looking at, these 2 seeds over on the left, you'll notice that, that these are differentiated as monocot and dicot. So here we have a monocot seed, and here we have a eudicot seed. And you can tell based on the cotyledons, this one has just 1, this guy has 2, and you can see the other seed parts, including the seed coat, that protective outer layer, the endosperm, which is going to be the nutrients that the embryo feeds on, and also, we'll have this structure here called the epicotyl, and that is something that some plants have. It's kind of like an embryonic stem, but it's an embryonic stem that extends beyond the cotyledons. So, when our plant sprouts, this becomes more readily apparent. And we'll actually talk about sprouting when we flip the page.
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Germination
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Once our plant embryo is formed and our seed is all set, it still has to somehow turn into a fully formed plant. This begins with germination, which is the process by which a plant forms from a seed. And it usually occurs after water is absorbed by the seed, through a process known as imbibition. Now, the seed coat, as we've said before, is that protective outer layer, and it forms from the integument. Which you might recall as a structure found in the ovule. Now that outer layer is tough, and so while sometimes imbibition will be able to cause enough swelling that it can break the seed coat open, and sort of free the plant to, develop, some seed coats are actually too thick to absorb water, and require some type of physical penetration in order to germinate. In some cases, this could actually require, being, you know, for example, like chewed up and digested a little by an animal or something before the seed can actually germinate. Now, the way a seed will sprout depends on whether the plant is a monocot or a eudicot. See, eudicots will have a hypocotyl that curves and grows towards the surface, and essentially pushes the cotyledons out of the soil. So you can kinda see that happening in this diagram here, where this hypocotyl will be curved, and it will grow up, and push its way out of the soil, and once it's out of the soil the, cotyledons will actually sprout out of this seed. Now, in monocots this happens a little different. Monocots will actually push their shoots straight up through the soil, whereas in the case of eudicots, the hypocotyl, right, that embryonic stem is curved, and you can almost think of this as like a process of the plant like arching its way out of the ground. In monocots, this is more of a straight shot. And because of that, monocots actually have to have these protective structures that, help their emerging roots and shoots. And we call those the choliorhiza and, choleoptyle, depend, and the choleurrhiza is the, first structure to actually emerge from the seed, let me hop out of the way here, you can see it here, and it is protecting the radical, and you might, I hope you caught the spelling mistake in this figure, radical is supposed to be spelled like that. I just liked the spelling mistake too much to take it out of the figure, because this is basically spelled like, you know, like radical dudes. So, anyhow, the choleraizer protects the radical, and the cholioctyl protects the cotyledons, which you can see as these little structures here inside the coleaptile. Now, hopefully, as you can see in this image here, here's our seed, it's going to stay where it is. And from here, its shoots are gonna push up, and its roots are gonna push down. So whereas the eudicot, again, did that curving, pushing out of the soil. Right? This is gonna have the seed stay where it is, and it's gonna push its shoots and roots out from that point. Now, how do these seeds get where they need to go? Well, seed dispersal is the technical term for the transport of seeds away from the parent plant, and there is a number of ways this can happen. You can have wind disperse your seeds, water, also animals, as we can see with this dog here that is covered in burrs, which are seed pods for plants. Now, oh, and here also you can see, these little plumes from a dandelion. Here is the seed, and this tuft on top is to help it, help the seed be dispersed by wind. Now, seeds don't germinate right away when they land in dirt. They actually, and can enter a period of dormancy, and will actually wait to germinate until the conditions are favorable. And in the case of sun seeds, this could be years of dormancy before germination. Alright. Let's turn the page.
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concept
Fruit
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3m
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One way to encourage animals to disperse your seeds, aside from having them stick to your fur, is by putting them in fruit, which, of course, is delicious, and we animals love to eat. So fruits are technically these seed bearing structures that form from the ovary after flowering. Now, as you can see in this diagram here of a peach, or it really could be any stone fruit, you have your seed on the inside there, with its endosperm, embryo, and seed coat, familiar structures to us. And then surrounding it in this area we have what's called the pericarp, And this is the part of the fruit that we eat, and this is what ripens from the ovary and will surround the seeds in a sweet delicious coating. Now, as I'm sure you're aware there are many different types of fruit and they take all sorts of shapes and sizes, and in fact, we call a lot of fruits vegetables, even though they're technically fruits. For example, zucchini, technically a fruit. Right? It's got that ripened ovarial ovarian walls surrounding seeds. Not that sweet, which is why we call it a vegetable, but technically it is a fruit. And, of course, amongst fruits that we think of as fruits, there's a ton of variation. And what we'll see is that these are actually due to different types of development. So you have simple fruits, and these are fruits like cherries. They develop from a single flower with a single carpel, or fused carpels, so a single pistol or a single carpel. And, these will have, you know, a simple structure like a cherry, that ovarian wall surrounding the little seed in there. And this forms from, again, one flower with its single pistol, or single carpel. Now you can also have aggregate fruits, which develop from single flowers that have multiple carpels. And an example of this is the raspberry. So even though this develops from a single flower, all of these little, juicy balls in Alright. Maybe I should think about my phrasing there. All of these little morsels in the raspberry form from separate carpels, and they each have a seed in them. Those are again called aggregate fruits. We also have multiple fruits, which develop from multiple clustered flowers, And a nice example of this is the pineapple, which, you can kind of see in its structure how it would develop from clustered together flowers. And lastly, we have accessory fruits, which develop from ovary tissues, as well as tissues outside the carpal. And a nice example of this is a strawberry, which has its seeds on the outside, and has its delicious fruity meat, inside the outer coating of seeds. So, many different types of fruits that result from different types of flowers. And that's all I have for this lesson. I'll see you guys next time.