Hi. In this video, we're gonna talk about seed plants. Now seed plants are made up of angiosperms and gymnosperms, and remember that they're a myophyletic group, meaning that the seed just evolved once and split off, towards angiosperms in one direction and gymnosperms in the other. Like all vascular plants, they have a sporophyte dominant life cycle. But unlike the seedless vascular plants, most of their gametophytes are actually microscopic, so they're even more diminished. And these actually can develop within the sporangia. Now, most seed plants are heterosporous and contain microsporangia that produce pollen and megasporangia that are found inside ovules, and we'll talk about what ovules are in just a second. Now, it's also important to note that most of these plants will have the microsporangia, which is the male part, right, and megasporangia, the female structure, on the same plant. However, some will be found on different plants. Now, you can see here, we have, 2 types of cones, these are, you know, the technical term is strobili, and here we have the male one that is going to house microsporangia, and here we have the female version that is going to house the megasporangia. So the ovule is the structure that contains the megasporangium and the megaspore, and it's actually what's going to develop into seed after fertilization. The outer protective layer of the ovule is known as the integument, and it's made of sporophyte tissue. And you can see that gymnosperms have this singular integument, whereas angiosperms have multiple integuments. And don't worry so much about, memorizing all the facts about gymnosperms and angiosperms right now, we'll be going into much more detail in, about plants in other chapters. So, the opening at the apex of the integument is called the micropyle, you can see them here in these ovules, and this, outer wall in the angiosperms is the ovary wall. So the angiosperms are gonna actually have this ovary that is going to cover the ovule, and that's actually what develops into fruit. So, basically when you're eating fruit, you're eating plant ovaries, and they're delicious. Now, pollen grains are the, male gametophyte covered by pollen wall. Right? This is a made of sporepollenin, and it's a a tough struck tough coating. It's gonna help protect the, interior. And these are produced by the, microspores. The pollen grains are produced by the microspores, and when the pollen travels to the ovule, we have pollination. And pollination syndrome is a term that refers to flower traits that have evolved in response to pollen vectors like wind, bees, and birds. So in essence, pollination syndrome is sort of a group of traits that have evolved, specifically to, or specifically in response to certain pollination vectors, and there there are tons of pollination vectors, many more than I've listed here. Now, seeds, which we can see right here, these are seeds, or this is a seed, these are ovules. Seeds develop from fertilized ovules, right, so this is going to turn into, well, this, I should say, is going to turn into that. And, they contain the embryonic plant, which you can see right here, I'm going to jump out of the image, so it's easier to see. The embryonic plant, which is this structure right here, and they also have this protective seed coat, which, allows seeds to stay dormant but alive for, quite some time. Now, the cotyledons are these little, embryonic leaves contained in the seed, and they will germinate to form a sprout. You can see they've been labeled here, but our cotyledons are actually, these structures right here, I don't know what these arrows are pointing off to. So let me redraw those, the cotyledon arrow, these are the cotyledons. Now, the endosperm is basically the food for the embryonic plant, and it's all the stuff surrounding the embryo. So if you eat a seed, mostly what you're eating is endosperm. If you've ever broken a peanut in half and noticed the little notch, on the end of it, that is the embryonic plant, and the majority of the nut is the endosperm. Alright, with that, let's flip the page.
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Seed Plants - 2
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Gymnosperms produce naked seeds. Basically, that just means that they're not enclosed by an ovary, like angio of gymnosperms are usually packed into cones. And as we were talking about earlier, generally, most plants will have, the male and female sporangia. Right? The male cone and the female cone on the same plant. We call these monoecious plants. Some plants however are dioecious and you'll actually find the male and female sporangia on different plants. So those male and female cones will be found on different plants. They won't be found on the same individual. Conifers are probably the gymnosperms you're most familiar with. These are like pine trees. And they're basically the group of gymnosperms that have those distinctive needle like leaves. Right? What, you know, we think of as just pine needles. I mean, there's many different types but that's a feature that defines the conifers. And also their sporangia are contained in those cones which are technically called strobilae. Now the cones are actually modified, leaves, right? They're sporophyll. And the pine needles represent an evolutionary, modification of the leaf that has a very thick cuticle. And this helps, these plants prevent water loss because, you know, conifers I mean, there are conifers all over the place but they can live in areas that have, you know, restricted access to water. So these pine needles allow and especially in the winter time they live in cold places where it can be very hard for the roots to obtain water due to frost and and the freezing temperatures. So these pine needles are an evolutionary trait that allows them to really prevent water loss, very effectively. Now, let's take a look at the life cycle of a gymnosperm When the pollen grain reaches the ovule It's actually going to, germinate and form what's called a pollen tube that digest its way through the megasporangium. So here we have our pollen grain. It's gonna get to our it's gonna get to the ovule and then here you can see the pollen tube digesting its way through the ovule to the megasporangium. Now the mega spherocyte is going to undergo meiosis and produce 4 haploid cells. One of which will become the mega spore. And the, megaspore will actually develop into a female gametophyte containing multiple eggs. When the pollen tube, reaches the eggs it's going to eject sperm that will fertilize the egg and then the ovule will become a seed. And after fertilization, of course, we're gonna have formation of the embryo. And that is our little seed right here. It's resting on one of the scales of the cone. So if you look at a pine cone it has all these little scales, these little I mean they're like little diamond shaped things in the in the figure but, you know, they're little cone scales. Well, if you were to peel that back and look at it, that's where the seed develops, right? That's where your seed is going to be. Now, the seed of course will, get carried away and sprout into a sporophyte and that is what grows into, you know, these big hulking trees that of course will develop their male and female cones and repeat this cycle over again. Don't worry too much about memorizing all the aspects of life cycle of gymnosperms. We're gonna cover that in much more detail when we, take a deeper look at plants. This is just, meant to be sort of a broad strokes overview. Alright. With that, let's flip the page and talk about angiosperms.
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Seed Plants - 3
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Angiosperms are perhaps best known for their beautiful flowers and their delicious fruit, which surrounds their seeds. They're actually also the most diverse group of seed producing land plants. And angiosperms are generally classified based on how many their seeds have. Monocots have 1 cotyledon and eudicots have 2 cotyledons. You can see a monocot over here and notice how it just has the one leafy bit to it and over here we have a eudicot. Notice how it has 2 leafy bits on its sprout And yes, leafy bit is the technical term there. Now, you might be wondering why it's eudicot, you meaning true and not just dicot. The reason is the group actually used to be called dicots and included, other species that have since been rearranged into other lineages. And those other major lineages are basalangiosperms and magnoliids. Now, let's take a look at the flower. The defining feature of the angiosperm. The flower is the reproductive organ of angiosperms and it has, many parts to its anatomy. You've probably taken note of these if you've looked at flowers before but you may not have known all the terms for each of the parts. So to begin there's the sepal which if you've ever seen a flower bud, it's that those green leaves that, encase the little flower bud and when the flower bud matures, matures, they look like those, green leaf leafy bits underneath the petals. So right here, this part is a sepal. Now, we also have the petals obviously. These are modified leaves that surround the reproductive or, organs of the flower. And their purpose is, often to attract pollinators which is why they have, these beautiful colors and sometimes interesting patterns inside of them. Them. The stamen is like the male part of the flower. This is the pollen producing part and it's made up of the filament and the anther. And you can see a stamen right here. This is the filament or the stalk. There's also one marked over here. This is our filament. And here we have the anther, right, that nub on the end and if you've ever had fresh flowers, hang around your house for a little too long before, all of these stamen fall off, the anthers knock pollen everywhere and it's like a huge mess. Trick is you got to pull them out before the flowers die. Now, the carpal is like the female part of the plant. And some plants actually have multiple carpals. And if a plant has multiple carpals, they are referred to collectively as the pistol. Now, the carpal is also made up of different parts and you can see, we have the carpal right here. And the top of the carpal, which, let me use a different color, the top of the carpal is referred to as the stigma. The portion that goes from the stigma down to the ovary is called the style. And, you can see the style is this portion here. The ovary is this lower portion that contains the ovules which will become the seeds in the fruit. Now over here we have another, another ovary or I guess they're showing the stigma as well. So, I guess technically this is a a carpal, full carpal, though the top of this image is a little cut off. So that's why it looks a little funny. But anyways, within within the ovule, here is our, embryo sac. It's, basically the female gametophyte inside the ovule. And you can see here a pollen tube is extending to it. And, of course, fruit is formed from the ovary. Right? This portion, the ovary of the carpal. Alright. With that let's turn the page.
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Seed Plants - 4
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Hello, everyone. In our last lesson we talked about the anatomical structures of flowers. Now we're gonna talk about the different types of flowers that you can find on different types of angiosperms. Okay. So, we previously talked about things like sepals, petals, anthers, filaments, and things like that. Right? The structures that you find within a flower. But those structures can vary depending on which type of flower you have. So, there are complete flowers, incomplete flowers, perfect flowers, monoecious flowers, and dioecious flowers. So what we learned about previously, what we saw previously, were complete flowers. They contain sepals, petals, stamen, and pistils. So sepals and petals, and remember that stamen includes the anther and the filament, and these are gonna be the male structures that create pollen and create sperm. And then, pistils include the stigma, style, and ovaries, which are gonna be the female components of the flower, which create the egg and will eventually create the seed or the fruit. Now, if it is missing, if a flower is missing any of those four structures it is considered an incomplete flower, if it's missing any of those structures. Otherwise, it is a complete flower. Some examples of complete flowers are gonna be hibiscus flowers, roses are complete flowers, pea plants have complete flowers, and I believe tulips are also complete flowers as well. There's many more examples, but those are just a couple. Okay. So, now let's talk about the perfect flower. You may think that the perfect flower and the complete flower are probably the same thing. It's actually not true. They have kind of confusing names. You would think a complete flower would be a perfect flower, but in fact it's not. A perfect flower is going to be a flower that is bisexual. What that means is that it has male and female structures in the same flower. So that means it has a stamen and pistils. So, this is stamen plus pistol. Now, you may be thinking, oh, well then it's probably a complete flower. No. Because it doesn't have to have sepals and it doesn't have to have petals and it can still be qualified as a perfect flower as long as it's got a stamen and a pistil. So, perfect flowers can be complete flowers, but complete flowers are not always perfect flowers. So, monoecious and dioecious are gonna be 2 other types of flowers. So, monoecious and dioecious, you've heard those terms used before, generally, when you're talking about animals and the sexes of animals. So, monoecious plants, or monoecious angiosperms are going to have unisexual flowers. That mean the that means that the entire flower is either male or female. Either only has anthers or only has pistols. But, these male and female flowers are found on the same plant. So what that's going to look like is if we have a monoecious species of angiosperm. What we're going to have is, let's say we have these 2 bushes here, and they are the same species of angiosperm. We're going to have male flowers, and we're going to have Female Flowers in red. So, Male Flowers in blue, Female Flowers in red. So, if we have these two individuals of the same species, they're going to have male and female flowers on the same plant. So both of these plants will have blue and red flowers. They will have both sexes of flowers on the same plant. This is monoecious. And, generally, when we talk about monoecious organisms we're talking about hermaphroditic organisms, organisms that possess both qualities of both sexes, and these angiosperms do fit that category. Now, diolecious flowers or Dialysis Angiosperms also have Unisexual flowers. Meaning that they have male only flowers and female only flowers. However, these are found on completely different plants. So what is that going to look like? Dioecious is going to look different, because now if we have the same two plants, but this species is Dioecious, We're going to have 1 male plant and 1 female plant. So, let's say that this is the female plant with the red flowers and then one male plant with the male flowers. That is a dioecious species of angiosperm. And that's because dioecious is generally referring to 2 different sexes. Human beings are dioecious. There are individuals that are solely male, and there are individuals that are solely female. The same thing is happening with these particular plants. They have male flowers that are only found on the male plant, and female flowers that are only found on the female plant. These are dioecious species. So there are different types of flowers on different types of angiosperms. So, some examples of plants would be things like squash and corn have both male and female flowers on the same plant. Some examples of dioecious plants, or dioecious angiosperms would be things like willow trees. If you've ever seen a weeping willow, it's dioecious, holly, sassafras, and also poison ivy is an example of a dioecious species. There's male and female plants. There are many other plants. Those are just some examples of the 2 different categories. Okay. So now since we talked about flowers, let's talk about the different forms of pollination that you can have dealing with those flowers. So first, we're gonna talk about cross pollination. Cross pollination is where pollen is transferred from one plant in the species to a completely different plant in the species. So, basically, one individual is fertilizing a different individual. Now, this is going to be what is preferred in the reproduction of Angiosperm Plants. And that is going to be because this allows for genetic diversity. It is sexual reproduction. This is how 2 separate individuals are going to mix their genetics to create a zygote and eventually a seed or a fruit which will create the new plant. Now, this is in contrast to self pollination. If an organism or an angiosperm self pollinates, it is able to take pollen from its own anther and fertilize its own egg in the ovary. So, that is self pollination. This is not particularly preferred because this is basically cloning yourself. You're basically not making any new, you're not making any new genetic diversity here. Cross pollination is preferred, but some plants also can perform self pollination if need be, if they need to reproduce. But cross pollination makes genetic diversity, and that is what they're looking for. Okay. So now, let's talk about double fertilization. In fact, angiosperms do this really unique process called double fertilization. Usually, when you think about fertilization, you think of the sperm fertilizing the egg to create a zygote. That's single fertilization And that's how a lot of reproduction happens. Angiosperms, however, do double fertilization. This is where a sperm fertilizes the egg to create a zygote. And another sperm is utilized to fertilize what's called the Polar Nuclei, which are gonna become the Endosperm. So, let's scroll down and let's look at a diagram of this. So, this here is going to be a diagram of the overall Angio life cycle. I'm gonna go out of the picture so you guys can see the rest of this. So let's start on this side here. We see that the anther is creating the sperm and is creating the We see that the anther is creating the sperm and is creating the pollen grain. You can see the pollen grain right here. And the pollen grain is then going to be, used for the process of pollination either by wind, or by pollinators like birds, bees, and butterflies. And the pollen is then going to be transferred to the top of the stigma on the, on the female aspect of the plant. So then, the pollen grain attaches to the female aspect of the plant, and it begins to create this pollen tube. And the pollen tube travels down into the ovary to fertilize an egg. Once it has reached an egg, then the sperm, which you can see right here, these are the sperm. The sperm are going to travel down the tube, and they are going to fertilize the egg, and they're also gonna fertilize the polar nuclei. You can see that process happening right here. The egg is going to be fertilized. That's the first round of fertilization. And the second round of fertilization is where the polar nuclei cells are going to be fertilized. Now, what's the point of the polar nuclei nuclei cells? Those are going to create the endosperm. And you can see the endosperm right here. So we have the embryo and the endosperm, the results of the 2 fertilizations. The embryo obviously will become the new baby plant, and the endosperm is going to be the nutritional substance inside of the seed that is going to allow the baby plant to grow. You can kind of think of it like the yolk of an egg. It is there for continue to continue to grow and to get out of the shell of that seed to create a seedling. So, the endosperm is going to be the nutrition. And this is going to be the process of double fertilization. 1 fertilization is used to create the embryo and the other fertilization is utilized to create the endosperm, embryo, and this is going to be a characteristic that is very unique to angiosperms. Okay, everyone. Let's go on to our next topic.