Nonvascular Plants - Online Tutor, Practice Problems & Exam Prep

Nonvascular plants, or bryophytes, include mosses, liverworts, and hornworts, characterized by a gametophyte-dominant life cycle and the absence of vascular tissue. They reproduce via homospores, with male and female gametophytes often on separate plants (dioecious). Key structures include gametangia, with archegonia producing eggs and antheridia producing sperm, which require water for fertilization. The sporophyte, attached to the gametophyte, contains the sporangium that produces haploid spores through meiosis, continuing the $n^2$ cycle of alternation of generations.

Nonvascular Plants - 1

Hi. In this video, we're going to talk a little bit about nonvascular plants. Nonvascular plants or bryophytes, as they're technically called, are plants that include mosses, liverworts, and hornworts. You can see a phylogeny of this right here. We have the Embryophytes, which includes all the different types of plants we'll be talking about. And then here, we have our bryophytes. You can see that vascular plants are a separate lineage. And remember that the defining feature of these organisms is that they don't contain vascular tissue reinforced with lignin. Although some may have transport tissues that use cellulose to maintain their rigidity. You can see an example of moss, liverwort, and a hornwort, right here. Don't worry if you can't really tell these apart; I mean, hopefully, you've seen moss before, if you've never seen or heard of liverwort or hornwort, not a big deal. These are just little, low to the ground, very simple, extensive nonvascular plants. Now, as we previously discussed, they have a gametophyte-dominant life cycle, which is going to change in later lineages to a sporophyte-dominant life cycle. And these organisms are also homospores, meaning that the spores they produce are all of the same type. Some species have bisexual gametophytes, meaning that the male and female reproductive, or the male and female gametophytes rather, are located in the same plant. Some species, like mosses for example, have separate male and female gametophytes. So the male parts and the female parts are found in separate plants. Here we have an example of a moss life cycle. And we can just kind of use this as a stand-in for our nonvascular plant life cycle. So I'm just going to quickly walk you through this image; jump out of the way here. So spores give rise to the gametophytes. Right? And here we have our male gametophyte, here we have our female gametophyte. It's through mitosis that these spores will develop into the gametophytes. Here you can see we have the fully developed male and female gametophyte. And you might notice there's actually an error in this diagram. I didn't make it. It's really not a big deal, but you know, here it says female, and here it's male. You know, these arrows should be reversed; sorry. I didn't make the figure. But it shouldn't really affect your understanding. Obviously, the female gametophyte spore is going to develop into the female gametophyte and the male gametophyte spore is going to develop into the male gametophyte. So just remember that these arrows are crisscrossed. Anyhow, these gametophytes are going to produce the sperm and the egg. And remember that the sperm requires water to get to the egg. And the structure that produces the sperm is called the antheridium, the structure that produces the egg is called the archegonium. Don't worry; we're going to go over this again on the next page. So when the sperm and the egg get together, we're going to have fertilization. A zygote is going to form, right, and that is going to develop into an embryo. And everything on this side, remember, except for the zygote here, needs to note that zygote is 2n. All this other stuff is n. Right? And it's indicated in the figure that these are all haploid. All this stuff, of course, except for the zygote. Right? The zygote's diploid. They don't actually show it in the figure, but when the sperm and the egg combine, they're going to form the zygote. So everything over here is diploid. Diploid. Right? So this is the dominant part of the life cycle. Basically, what that means is the part of the plant we're used to seeing is going to be this haploid gametophyte part of the plant. This embryo that forms after the sperm gets to the egg, this embryo is going to sprout into this sporangium. Right? So this embryo, basically, is going to develop into the sporophyte. And the sporophyte, part of the sporophyte is the sporangium, which produces the spores. And those spores, remember, are going to be haploid, and the sporophyte produces them through meiosis. Those haploid spores then develop into the gametophyte and we repeat this cycle. So, you know, this is just basic alteration of generations. The things to bear in mind are that water is necessary for the sperm to get to the egg. And those terms antheridium and archegonium, don't forget, we're going to talk about those in just a moment. So with that, let's flip the page.

Nonvascular Plants - 2

So let's go over a bunch of terminology. Again, gametophyte, that's the gamete producing part of the bryophyte. Hopefully, that term is very familiar by now. And in the case of bryophytes, because they have a gametophyte dominant life cycle, the gametophyte is the part of the plant that we're most familiar with. And remember, that bryophyte gametes require water. Right? Water is needed to move the sperm to the egg. The gametangia is the organ or cell, in which the gametes are produced. And they're contained in something called a gametophore. Now, remember, that there is a sort of like male and female dichotomy here. So there, the gametangia can produce male or female gametes and if it produces female gametes, then we call it archegonia. Right? That's the female gametangia and it's going to produce egg cells. And this is where fertilization is going to occur. Right? The antheridia is the male gametangia and that's going to produce sperm which are going to go to those eggs to do fertilization. Now, taking a look at our figure here, you can see the male and female plants. And here, this is what the top of our male plant looks like, that's our male gametangia. Right? This is our gametophore. And we have the antheridium and the sperm in there. So, the antheridium is the structure that's going to produce those sperm. This whole thing is our gametophore. Oops. And then, of course, here we have the female side which is the archegonium. So let me write that in. This is the archegonium. And it's 'gonium' because we're dealing with a single archegonium. That's the singular form of the word. Archegonia is the plural. And here you can see our egg inside the archegonium. And, as we said, those sperm are going to need water to get to the egg. Now, some species, as we mentioned previously, some species actually are bisexual. That is they will have the archegonia and antheridia in the same plant. We call those monoecious. So that's just a monoecious plant is just one that bears the sperm and the egg in the same gametophyte. A dioecious plant bears sperm and the egg on separate gametophytes. So these mosses that we're talking about, these mosses are dioecious. Right? Because the male and the female parts, or male and female gametophytes rather are on different plants. And notice how in this figure it says nonvascular leaves, right, and nonvascular stem. This is a nonvascular plant, so it's going to lack those vascular tissues, and it can't have leaves in the sense that we're used to thinking of leaves because it doesn't have vasculature. So these are nonvascular leaves in quote, quotes. Also, technically, these aren't roots because, again, roots require vascular tissue. These are what are called rhizoids. They are functionally like roots. They're very similar. The difference is that they don't have those vascular tissues, but they serve the same purpose. But we have to give it a different name to distinguish it. Now moving on, let's take a look at the sporophyte. So we just looked at the gametophyte anatomy. Let's look at the sporophyte anatomy. So the sporophytes in these nonvascular plants are going to be the small structures. Right? This is the part of the plant where not you really like when we think of moss or, you know, you probably have never thought of a liverwort, but if you were to, you wouldn't really be thinking about the sporophyte, you'd be thinking about the gametophyte of that organism. And that's because, again, these organisms have a gametophyte-dominant life cycle. Now the sporophyte, that's the structure that contains the sporangium, which is what makes the spores. And the sporophyte has a couple of features to it. It has what's called the foot. And the foot is basically the attachment to the gametophyte and it absorbs nutrients from the gametophyte. And then you have the seta which is basically like the stalk of the sporophyte and it's going to transport nutrients up from the gametophyte to the capsule. And the capsule is that top of the sporophyte and it's the sporangium structure, basically. It is the structure that contains the sporangium. You can see another view of this here. We have the capsule, and you can see some spores being produced and coming out. Right? And of course, those spores are going to grow into the gametophyte, which is sort of what's being shown in this image here. It's like the growth of the gametophyte starting out as a little bud with little rhizoids and then growing into a full-fledged gametophyte. And this, this early structure, which is really just a chain of cells that you see right here, that grows from the spore and develops into the gametophyte is called the protonema. And it's, again, it's just a little chain of cells that grows out of the spore and develops into the gametophyte. It's kind of like the sprout of the nonvascular plant. Alright. That's all I have on this video about vascular plants. I'm sorry, nonvascular plants. So I'll see you guys next time.

Here’s what students ask on this topic:

What are nonvascular plants and how do they differ from vascular plants?

Nonvascular plants, or bryophytes, include mosses, liverworts, and hornworts. They lack vascular tissue, which means they do not have specialized structures like xylem and phloem to transport water and nutrients. Instead, they rely on diffusion and osmosis for these processes. This limits their size and makes them dependent on moist environments. In contrast, vascular plants have a well-developed vascular system, allowing them to grow larger and inhabit a wider range of environments. Nonvascular plants also have a gametophyte-dominant life cycle, whereas vascular plants typically have a sporophyte-dominant life cycle.

What is the life cycle of nonvascular plants?

The life cycle of nonvascular plants, or bryophytes, is gametophyte-dominant. It begins with haploid spores that develop into gametophytes through mitosis. The gametophytes produce gametes in structures called antheridia (sperm) and archegonia (eggs). Fertilization requires water for the sperm to swim to the egg, forming a diploid zygote. The zygote develops into a sporophyte, which remains attached to the gametophyte and produces haploid spores through meiosis. These spores are then released to start the cycle anew. Key stages include the protonema, gametophyte, and sporophyte phases.

What are the key structures involved in the reproduction of nonvascular plants?

In nonvascular plants, key reproductive structures include the gametangia, which are organs that produce gametes. The male gametangia, called antheridia, produce sperm, while the female gametangia, called archegonia, produce eggs. Fertilization occurs when sperm swim to the eggs, facilitated by water. The resulting zygote develops into a sporophyte, which contains a sporangium that produces spores through meiosis. These spores then develop into new gametophytes. Other important structures include the protonema, a chain of cells that grows from the spore and develops into the gametophyte.

What is the difference between monoecious and dioecious nonvascular plants?

Monoecious nonvascular plants have both male and female reproductive structures (antheridia and archegonia) on the same gametophyte. This means a single plant can produce both sperm and eggs. In contrast, dioecious nonvascular plants have separate male and female gametophytes, meaning one plant produces only sperm and another produces only eggs. This separation can affect the plant's reproductive strategy and reliance on environmental factors like water for fertilization. Mosses, for example, are typically dioecious, with distinct male and female plants.

Why is water essential for the reproduction of nonvascular plants?

Water is essential for the reproduction of nonvascular plants because their sperm are flagellated and require a film of water to swim to the eggs located in the archegonia. This dependency on water limits their habitat to moist environments where water is readily available. Without water, the sperm cannot reach the eggs, and fertilization cannot occur, halting the reproductive cycle. This reliance on water is a significant factor in the life cycle and distribution of nonvascular plants.