Okay, we're going to look at the life cycle of mosses, which for our purposes will be our best example of the non-vascular plants. Most plants that we are familiar with are vascular, which means they have tissue that actually carries water and nutrients and materials throughout the plant. But mosses are the most primitive plants and they are non-vascular.
vascular. So in order to do this we are going to pull up an image. So here is our image of the moss life cycle and when you first look at one of these life cycle drawings, it's kind of confusing but first thing you always want to note is the direction. This one moves in this direction as noted by these arrows that show us the way it's going and This is obviously a cycle so there's not really a beginning point or an ending point. So we can just pick an arbitrary place but where I like to start is I like to start with fertilization.
Because that is where life begins, that's where the egg and sperm come together and make the new organism. And so that's where we're going to start. Fertilization, if you will recall, always involves the same thing. It always involves a sperm and an egg.
which are both haploid, coming together and forming some type of zygote, which is going to be a diploid creature, diploid creation. And so, if we start with fertilization, which is, as we said, right here. And then we're going to kind of go from there. So what we're going to see in this diagram is everything in this kind of, I don't know what color that is, kind of a brown cream kind of color, is going to represent diploid organisms.
So everything after fertilization is going to be diploid. Now one good strategy when you're looking at any of these life cycles is to draw a line through it. And the only way, what we're going to do is this bottom... The under part of this line is going to represent being diploid, and the top is going to represent being haploid. And the only way to get from haploid to diploid is through fertilization.
On the other side of that spectrum, the only way to get from being diploid to being haploid is through meiosis, which is the cell division and sexual reproduction that cuts the number of chromosomes in half. half. So after fertilization, fertilization is going to take place in what's called the archegonium, which is the female part of the life cycle of the moss.
And the archegonium is what actually holds the egg. And once it's fertilized, the archegonium is going to hold the zygote, which is of course going to be diploid. The zygote is going to turn into the embryo, which will just divide by mitosis. If you recall, meiosis is going to produce sexually recombinant genes. It's going to be recombinations and produce diversity of genetics and obviously haploid cells.
But mitosis is going to be what we actually do in the embryo to grow. and to develop. And the embryo is going to produce what is called the sporophyte generation.
If you'll recall, phyte just simply means plant, and sporophyte has to do with the spores that will be made by the sporophyte generation. And so, this sporophyte is actually going to grow up out of the archegonium. And if you look in this next little image, these little things that kind of look like they have a bowl on the end, those are the sporophyte generation of the plant, and they are diploid, and they are going to produce spores. And those spores are going to be produced in this little container right here, which is called a sporangium, and it has inside of it cells that are going to go through meiosis and create...
haploid spores. So spores are actually produced by meiosis and they're haploid and each of these spores is going to be slightly different from the other because as we know meiosis produces cells that are not genetically identical to one another. Now, some of these spores are going to go on and become more archegonia.
So the archegonia are going to have the eggs inside of them, and they'll be fertilized and continue the process, just like we talked about there. But some of these spores are going to go on to become the male part of the moss life cycle, which is called anthridia, and the singular of that is anthridium. Now this is the part of the moss that you normally see. When you're looking at moss and you see the green part, this is the photosynthetic part. And this is called the gametophyte generation.
And so it is actually the part that does photosynthesis. It's the dominant part of the moss life cycle. And that's going to change when we get to vascular plants. It's actually going to be the sporophyte generation that's dominant. But the antheridia are the male part, and the archegonium, the archegonia are the female part, and the male part is going to produce sperm, but it's going to produce them by mitosis, which is very different from our life cycle.
Life cycle in animals, sperm and egg are produced by meiosis, but in the moss life cycle, meiosis produces spores, and then by mitosis, those spores are going to produce sperm or egg depending on if it is the anthridia or the archegonia, if it's the male or the female part. Now, one thing about mosses is they are very closely tied to water. They have got to have water, usually in the form of rain or maybe seasonal flooding or dew in the mornings, but mosses you're always going to find in very wet.
environments because they've got to have that water to reproduce and the reason why is because they have flagellated sperm which means that the sperm have flagella on them and they need to swim and this is a remnant something that is left over from plant evolution if you look at the predecessors of the plants the protozoans that the algaes and the green algaes that plants came from They have flagellated sperm. And these sperm are going to swim. They're actually going to swim up and down into the archegonium.
And they're going to fertilize the egg that's down in there. And then we're back to where we started fertilization. So if we want to do a very quick review of the moss life cycle, we could start here with fertilization. So the sperm and the egg come together. and they produce a diploid zygote, which is that first single cell we all start as.
That develops into an embryo. The embryo grows up into the sporophyte generation, and that's not a very good sporophyte, which grows out of the archegonium. And then these sporophytes are then going to have cells inside of them that undergo meiosis. And...
produce haploid spores, which are all genetically differentiated. Some of those spores will become female gametophytes called Archegonia, and they will have eggs in them. Some of them are going to become male gametophytes, which will be Anthridia, and they will produce sperm, and the sperm and egg will come together in fertilization, and the whole process will just continue on in an endless, endless cycle.