monday we're going to talk about the reproduction of flowering plants and with that reproduction there's quite a bit of new terminology and we've been working from this very general life cycle of a plant so i just want to walk through a few details of the life cycle that we're going to focus on first we're going to talk about the multicellular gametophyte and the multicellular sporophyte there are two key phases in any alternation of generations or diplontic life cycle and we refer to these as the gametophyte and the sporophyte the gametophyte is always haploid and multicellular and the sporophyte is always diploid and multicellular and then there's this alternation between that haploid phase and the diploid phase to go between go from diploid to haploid we have to use meiosis but for all of the other transitions we use mitosis each of the phases are named based on the structures that they produce so the sporophyte makes spores and the gametophyte makes gametes one thing to notice is that sporophytes make spores spores are haploid sporophytes are diploid so in order to produce a spore you have to go through meiosis but because the gametophyte grows from the spores it's already haploid the gametophyte is already haploid so when it goes to produce the gametes it does it by mitosis and this makes the alternation of generations of life cycles very different from animals we think of our gametes as being produced by meiosis while in plants the gametophyte produces gametes and it has to do it by mitosis because the gametophyte is already haploid to get started in understanding how life cycles differ among different terrestrial plants or plants that live on land it's often easier to start with early plants as they've moved on to land so we talked about mosses as a group of plants that first moved on land and they were often the ones that use strategy one of how to adapt to living on land mosses are something that people see really often they just may not recognize that's what they're looking at you can see the moss is in the picture of the forest at the base of all the trees all of that very bright green plant material is actually a moss if you move counterclockwise from that picture and look at what looks kind of like a green blob you're kind of zooming in on that moss structure and then if you keep going counterclockwise and you zoom in very close as if you're holding that blob in your hand what you're looking at are little stalks with tiny leaf-like structures that do photosynthesis on a moss this is the gametophyte and the moss spends the majority of its time in that gametophyte stage so every little leaf and stalk you're looking at is made up of multiple cells the gametophyte is multicellular so what you're looking at there is a multicellular plant that spends the majority of its life haploid we often call plants that spend the majority of their life haploid or the majority of life in the gametophyte stage gametophyte dominant so if you hear someone say give me to fight dominant it means that the majority of life is spent in that multicellular haploid stage so the next thing to think about is how then does this plant go about running through its whole life cycle or when does it become sporophyte what does the sporophyte look like how does it make gametes all of those things fall under the life cycle so on the next slide we're going to look at the whole life cycle of the plant and try to orient you to the structures on the diagram while also looking at real images of that plant okay the first thing i want to tell you on this particular slide and for the majority of moss information is that you will not have to memorize this life cycle however there are several structures that are analogous to what we're going to talk about in flowering plants so even though you don't have to memorize these structures this will make it a lot easier to think about flowering plants when we get there so what you should see on the slide right now is the entire life cycle of the moss it looks really complicated so if you go ahead and click on your mouse you'll see that the life cycle goes away and what you're left with is the image of the mosses from the last slide and then the cartoon-like diagram from the top of the life cycle so when you see that image from the top of the life cycle you know you're looking at one of those individual stocks from the photograph all right so if you can then think about that what you'll notice at the top of those structures are there are two black circles surrounding parts of what we've called the gametophyte or the stalk of the gametophyte okay if you go ahead and click now what should happen is the image of the mosque goes away and what will appear are the arrows coming out of those two black circles and then two new images well four new images really showing you two different structures these are going to be the reproductive structures of the gametophyte remember the gametophyte is the structure that's making gametes so these two structures are going to be responsible for making the egg or the ovule and the sperm as you can see with the text next to the slide the archegonium is going to be the structure that makes and contains the egg or the ovule and when we fertilize that egg the embryo will grow within the archegonium we'll talk more about that when we get to that process of fertilization the male structure the part that makes the sperm and releases the sperm is called the antheridium so they show you two diagrams of them as if you were looking at them under low magnification and then they zoom in on the two structures the antheridium and the archegonium now in lab in order to look at the gametophyte at all you looked at the archegonium and i want to emphasize that that's just part of the gametophyte it's not the whole thing a lot of the moss does photosynthesis does not do reproduction so we the whole gametophyte includes all of the stock the parts that they're doing photosynthesis and then these reproductive structures so what you can see from this diagram is that the archegonium will contain the egg or the ovule the antheridium will produce the sperm again this occurs by mitosis now if you think about the fact that these structures every cell you're looking at is going to be haploid so that includes the sperm the cells mate that make up the archegonium the cells that make up the antheridium now i want to actually show you these when they look what they look like on a real plant so in the next slide we'll show you those we won't go into too much detail about them but just so you can get an idea of how different they really are okay in this slide what you can see are the structures that are called the archegonium and the antheridium on live moss plants and really if you're not looking for them it might even be hard to detect these independently from the photosynthetic parts of the plant and they're not always visible the gametophyte is not always producing sperm and egg but at this time of year because it's been so wet you could actually go out and look at mosses and see these structures starting to develop in lab you looked at the cross section of the archegonium and you can see that next to the archegonium image at the top of the slide now when you think about mosses we often kind of generalize and think of them all as the same thing but there are many different species of mosses and they all have these structures but they use them differently so in some mosses you can find the antheridium and the archegonium on exactly the same plant on other mosses you may see that one plant makes the archegonium and the other one makes the antheridium this will also be true in flowering plants where some flowering plants make one plant that is female and one that is male whereas others have the male and female parts on the same plant okay as we return back to the life cycle diagram we left off showing the antheridium and the archegonium producing sperm and egg when water actually hits the antheridium what it will do is it will cause the antheridium to release the sperm and the sperm will then swim into the egg and remember in early plants they still have flagellated sperm so they require that water droplet so the sperm can swim from the antheridium down through into the archegonium and fertilize the egg fertilizing the egg results in the production of a diploid cell so a haploid sperm comes into contact with the haploid egg the two nuclei of these cells fuse together to form the embryo and that makes the embryo diploid but until that diploid diploid cell goes through one round of mitosis it's not multicellular yet so we're not quite at the sporophyte stage just yet if the embryo undergoes mitosis however that's when we start building the sporophyte in this diagram what you can see is that the embryo will start to develop on the arc or within the archegonium so on the gametophyte of the plant and it will start to go through mitosis until it produces a structure called the sporangium so if you go ahead and click you'll see a cartoon diagram of the moss with a brown structure coming out of it and that whole brown structure the top the stalk coming out of the archegonium that's all the sporophyte and as you click through what you'll see is images will pop up showing you the sporophyte in a real photograph and then also a cartoon drawing that indicates in two different ways that the sporophyte and the gametophyte are on the same plant and this is also something i think we often think of them as completely separate but in alternation of generations the sporophyte and the gametophyte are often together on the plant they're not separate plants and you can see that really clearly here with the mosses now the next part of the life cycle is the sporophyte making its reproductive structures the structure itself in the case of mosses is called the sporangium it is the structure where spores are produced now remember the cells of the sporophyte have to be diploid they're part of the sporophyte generation so they're diploid and multicellular but we'll have individual cells that go through meiosis to make the spores so if you go ahead and click through you should see that within the sporangium the spores are going to be made by meiosis then when those spores are released you'll see them start to germinate that means to grow and produce a whole new gametophyte by mitosis again so again the only meiosis part here is coming from cells within the sporangium okay so when you think about the cells that are actually going to go through meiosis you may know in from what we just talked about that the cells have to be within the sporophyte and they're going to be in this structure called a sporangium but you may not have thought about which cells are actually undergoing meiosis so to draw parallels between plants and what you already know i'm going to use the human male as an example human male meiosis is very much like what we teach you as basic meiosis whereas female meiosis is a little bit different and save that for when you're about reproduction in females later in the course so i think most people recognize that meiosis is only happening within the gonads right but when you get within the gonads the gonads are not all cells that are gonna all of the sudden undergo meiosis so some cells within the gonads do not go through meiosis at all however within the gonad in human males there's a cell that's called the spermatocyte so it's the spermatocyte and the spermatocyte is a diploid cell it'll go through meiosis one and you can see on the diagram that it produces something called the secondary spermatocyte from meiosis one and then after meiosis ii it makes something called a spermat spermatid so in this case the spermatids will then undergo a bunch of changes they get their flagella and do a few other things to make them truly sperm and then the sperm can be used to fertilize eggs so in the case of human gonads the cell that undergoes meiosis is called the spermatocyte in plants the equivalent cell is called a mother cell this is fine except for the fact that when we hear the term mother we think female but in reality the mother cell is any cell that can go through meiosis to drive home the point of this mother cell i'm showing you a very schematic diagram of how meiosis works in plants the mother cell is a diploid cell found within the sporophyte of a plant and it will go through the two rounds of meiosis meiosis one and meiosis 2 and as a result these structures that are produced are called spores the mother cell goes through meiosis and will produce spores this is going to be one of the key things that will trip up understanding how cells are produced in flowering plants so think about the mother cell as just a diploid cell that will be one responsible for making spores okay so how does the mother cell actually relate back to the life cycles that we're talking about what you see in the image is the diagram of alternation of generations that you've seen before and in the the moss we started out with the gametophyte we watched the gametophyte go through uh mitosis to build the archegonium and the antheridium the anthemidium and the archegonium make the sperm and the egg so the gametes by mitosis and then the gametes come together for fertilization it happens within the archegonium and it develops from the zygote to the embryo and once that embryo is multicellular we call it the sporophyte the sporophyte and the moss had that large sporangium on the top and we know that within the sporangium we're going to make spores so let's be specific based on what we know now and the cell within the sporangium that we're interested in is the mother cell so the mother cell within the sporangium will undergo meiosis and produce a spore then that spore can germinate and produce a new gametophyte or the new moss structure this process is the same in all plants in the in the sense that the mother cell will always produce the spore and then that spore will develop into the gametophyte what's going to differ across the different groups of plants is the length of time it spends in the gametophyte where fertilization takes place and things like that and if we move on to the next slide we can remind ourselves a little bit about what what the actual relationship between those differences among life cycles are and the adaptations to land as i just mentioned in the previous slide there's going to be variation between the moss cycle the gymnosperm life cycle and the angiosperm life cycles gymnosperms remember are the they're large land plants like pine trees they are vascular tissue they produce cones not fruits and flowers so when you look at the two life cycles on the slide i'm not expecting you to know those i don't want you to know the details of them but remember one of the things that changes as we get better adapted to land is the length of time that plants stay in that gametophyte stage or in the sporophyte stage so you can see just based on the color brown that the time spent in the sporophyte stage increases in gymnosperms and it's even more dominant in angiosperms we also see that the number of cells in the gametophyte will go down as we become better adapted to land so in the case of the moss it's a huge number it's making up all of the archegonium all the antheridium all of the photosynthetic cells but in pine trees and in flowering plants the number of cells gets really really small the pollen grain is actually the male gametophyte in gymnosperms and angiosperms and you're going to see that that goes from something like eight or nine or ten cells in in some plants to only two in in angiosperms so you're going to see a very drastic reduction in number of cells in the gametophyte now in the two life cycles you see on here all of them have flagellated sperm so they all have flagella however unlike mosses we don't require that water to disperse the sperm the sperm in gymnosperms is encapsulated by a structure called pollen and it's primarily wind dispersed in gymnosperms so now it doesn't need that flagella anymore even though it has it okay so that also means that the way that we get sperm to the ovule is very different it no longer relies on water and that's because they're better adapted to land and they're able to move away from water so they just don't have access to it so we see these changes happen and when we get really talking about those gametophytes we actually get really down to only talking about a few cells and so we get very specific about some details all right to draw another parallel between human sperm and egg and plant reproduction there are a few things that in biology the way that we name them is consistent across all organisms and when we designate something male or female it's done based on the size of the gamete right so we're switching from spores to gametes for a minute just to define male and female the large gamete is always produced by the female and the small gamete is always produced by the male so when you look at this image of the sperm and the egg you can see that the sperm is much much smaller than the egg and so you could flip it around too you could say well i found this new organism and i think i have a male and a female the one that produces the largest gamete i'm going to call a female and the one that produces the smaller gamete i'm going to call the male and that would fit in with a lot of biological definitions now that means that when we want to refer to females we often put prefixes in front of their names so if you see something that starts out with mega it can often refer to the female to indicate that this is going to produce the female structures in addition in males we would use a prefix called micro so something called a mega spore might make a female gametophyte and a microspore would make a male gametophyte okay so let's tie it all together so that you guys have all of the information that you could possibly want before heading into understanding how angiosperms reproduce now we've talked about the life cycle and the different structures that you some you saw in labs some you didn't see in lab and we did this from the perspective of mosses but we know that when you move away from land or water onto land you start to have some changes to the way the moss life cycle would work one of the things that we see happen is a change in the size of the gametophyte but we're also going to get some other differences that happen in angiosperm reproduction and these are going to tie together that mega and micro idea the mother cell idea and so i've shown you on this slide only the part of the diagram the generalized diagram that we need right now to focus on tying all these terms together some plants have male gametophytes and some plants have female gametophytes when they're separate that means that this one spore is going to produce a female gametophyte and one spore is going to produce a male gametophyte and these two spores are different they're going to come from different parts of the plant so we need to be a little bit more specific about where they come from and this is going to tie in that idea of micro and mega and we'll start with the the spore that produces the female gametophyte and that's the image that you see on the side right now so remember when you start with the multicellular sporophyte which in angiosperms is going to be almost all that you will ever see so the tree the trunk the flowers that's all sporophyte but within that sporophyte there's going to be a cell a single cell that goes through meiosis because in angiosperms we make a male gametophyte and a female gametophyte we're going to have a separate spore that makes the female gametophyte and a different separate spore that makes the male gametophyte so if you're in the sporophyte you want to differentiate the mother cell that goes through meiosis to produce the female gametophyte and the mother cell that goes about producing the male gametophyte so on this diagram that's currently on the slide what you see is that the multicellular sporophyte stage we still have the orange dot that indicates the mother cell but instead of calling it just the mother cell we call it the mega spore mother cell remember mega refers to the female and what this is describing is a cell that's going to produce a spore and specifically it's going to produce a spore that will grow into the female gametophyte this spore is going to be called a megaspore so the megaspore makes the female gametophyte or goes through mitosis to make the female gametophyte and the mother cell that produces the megaspore is going to be called the megaspore mother cell so if you walk through this within the multicellular sporophyte there's a cell it's diploid it's called the megaspore mother cell it goes through meiosis and its product is the megaspore that megaspore is going to grow into the female gametophyte and you know this because it has that prefix or the beginning of the word is mega that female gametophyte will then go through mitosis and produce the ovule or the egg right so if you walk through that one more time you know that on the multicellular sporophyte or within the multicellular sporophyte you have a cell called the megaspore mother cell it's a mother cell so it's going to go through meiosis but since it's a megaspore mother cell it produces a megaspore megaspores will then go through mitosis and produce the female gametophyte the female gametophyte can then go through mitosis and make the egg or the ovule okay that makes sense this is the one that's intuitive if you click we're going to then look at what happens in the male all right within the sporophyte again you have a sporophyte so it's multicellular and diploid and somewhere within that sporophyte there is a cell called the microspore mother cell now remember i told you mega refers to female and micro refers to male right so with the term microsport makes sense right a microspore grows into the male gametophyte what's weird about the terminology here is that there's a mother cell with the term micro and we think of mother as female and micro is male and things get confusing so when you see the term microspore mother cell what we're saying is this is the cell that's going to go through meiosis to produce the structure called the microspore so it you can ignore the fact that mother has female connotations here and instead think about the fact that the mother cell is something that goes through meiosis so within the multicellular sporophyte you have a microspore mother cell that microspore mother cell is going to go through meiosis after meiosis it produces a structure called the microspore that prefix microspore or microspore is micro so that means that once it goes through mitosis it's going to produce the male gametophyte the male gametophyte will then go through mitosis and make sperm so one more time in the case of a male part of a plant the multicellular sporophyte is the large part of the plant it's diploid and multicellular one of its cells that's also diploid is called the microspore mother cell the microspore mother cell goes through meiosis to produce microspores the microspores then go through mitosis to make the male gametophyte and then the male gametophyte can go through mitosis to make sperm all right so when you talk about these two things the female gametophyte in angiosperms is going to be called the embryo sac and the male gametophyte is going to be called pollen and we'll get to that on monday and hopefully these terms and practicing this will help you understand how angiosperms reproduce you