 All right. It was great to see this. Many of you here this morning. I didn't actually expect it with the exam tonight, so who knows all of you for showing up today and I've heard through the grapevine that some people are having difficulty locating the lecture notes that I've been posting So be sure to look for those on B space not on the bio 1b website You should have received emails after each lecture with the link to the lecture notes But if you didn't you can go to the the B space site log in with your Cal ID Go to my active sites the menu up in the upper left right of the menu and under there You should find the link which says bio 1b lecture plants Fall 10 and then click there and that'll take you to a screen where you'll see Resources as one of the choices on the left click resources, and you'll find the Lecture folder and just open that up and all the lecture Presentations are in there with the notes embedded in So please check that out. If you have trouble just give me an email Okay, also don't forget on Sunday night to change the clock back one hour Or you'll show up an hour early for lecture, which I'm sure you'd rather not do because I certainly won't be here then Okay So I'm going to start out today just going back over actually continuing this survey of the algae and Looking at the last major form of life cycle and it's actually the one we'll be looking at for the rest of the course So it's really important to in particular focus on this one Which isn't common to all the algae just some of them, but it's found in all the land plants and Then we'll get to some algal uses and then talk about the invasion of land by plants Which will be a theme into the next lecture as well Okay, I just want to make one jump back to the fungi though this slides you might remember about penicillin I just want to clarify what I was trying to get across here because it was a bit unclear the way I presented it that penicillin really the major point I was trying to make here is that the The cell walls of bacteria are different from the cell walls of all eukaryotes Okay, they're comprised of peptidoglycans which as the name implies are made up of an Amino of amino acids and sugars and Penicillin acts to interfere with the enzymes the bacteria need to synthesize the peptidoglycans And without their cell walls the bacteria will burst And so it's very effective as a medicine because of course we lack cell walls and fun Jai can get away with producing it because their cell walls of course are made of chitin Which is I mentioned that a few times earlier the same carbohydrate that arthropod Exoskeletons are made of or organisms like crustaceans and insects So I just want to add that extra context here. I hope that is a little clearer now All right, so as far as the algae go just want to recap the main points so far Before we launch back in Oops. Yeah, that's right. So Remember that the cyanobacteria the blue-green bacteria These share the ability to photosynthesize to use light to capture atmospheric carbon fix it as sugar and They're the only organisms that have actually evolved photosynthesis I shouldn't say the only ones but the ones that evolved photosynthesis that all the algae have subsequently taken advantage of so the evolution of photosynthesis by cyanobacteria represents the sole evolutionary event that resulted in photosynthesis and then all the other algalini just basically just captured cyanobacteria either directly or indirectly in Have taken utilized their Evolutionary innovation that way and only one Major lineage of the cyanobacteria gave rise to all of the plastids the chloroplasts and other plastids in the eukaryotic algae Okay, so that As far as I know, yeah That's that's all I'm only familiar with with Cyanobacteria, and one of the things We're gonna see there's quite a few single events and I mean we look back to the land plants They all seem to stem from one ancestor Photosynthesis seems to stem back to one lineage, but it's hard to say, you know if there were evolution if there were other Trial balloons out there that just didn't Succeed and they were outcompeted It's difficult. I mean with there may have been more than one origin of life on earth As far as we can tell there's just one lineage of life and all living organisms descend from that common ancestor But there could have been a lot of different You know living or semi-living whatever you want to call them types of things out there that couldn't compete with the organism That gave rise to life Well that all the photosynthetic eukaryotes have captured The cyanobacteria result from an event this endosymbiotic event Where cyanobacteria were captured and this basically this tree encompasses all the main lineages of eukaryotic organisms that descend from that That event and that includes all of the photosynthetic organisms the green algae as I'll point out later Ultimately gave rise to land plants. So this is this is pretty much it So it really does look like one event that gave rise to all the photosynthetic organisms that we call algae or land plants so again, we had this major divergence between This first major split between Eukaryotic photosynthetic organisms red algae on the one hand and green algae on the other And we'll talk about those groups in a little more detail in a moment But I wanted I was starting out first talking about some of these other Lineages that have originated from a secondary endosymbiosis or acquired their plastids They're chloroplasts by secondary endosymbiosis where they engulfed a eukaryotic photosynthetic organism either a green alga or a red alga and This led to a number of lineages. I didn't have much to say about this one because it's pretty minor But I did mention There's a major lineage here the eukaryotes which captured their chloroplast by capturing a unicellular green eukaryotic algae and They have a flagellum which allows them to move around quickly like you can see here It's very distinctive. It has some crystalline inclusion in it that you can do a section of it. It's very distinctive Their plastid is very much like a green alga. So that that in addition to the molecular data make it really clear But most of them actually can still capture prey they can still engulf prey and So it's even the pot that you can see that the potential for a secondary endosymbiosis You know to actually still engulf an organism that could be potential potentially become a symbiont is even still present in these Organisms even the ones that are photosynthetic in part in many cases Okay, and then the other main lineage the ones the secondary endosymbionts that captured red algae include these ones And I mentioned last time the dinoflagellates Which like the euglenaids are major components of phytoplankton and Remember phytoplankton just means basically plankton which are free-floating organisms in aquatic situations unicellular ones typically phytomines plant so photosynthetic basically So dinoflagellates Descend from a common ancestor with these other groups that had it Red alga Incorporated into their cells and a good number of the dinoflagellates are still photosynthetic Some of them have lost the ability to photosynthesize Strictly or heterotrophic and are actually pretty good predators in some cases But I showed you some photos Of these Last time and they have this external armor these plates of cellulose and cellulose again is the same Carbohydrate that we haven't gotten to this yet But in plants the cell walls that land plants have cell walls of cellulose as well But this appears to be an independent origin of that Anyways these have some interesting ecology especially in oceanic situations that I mentioned last time with the red tides and toxins bioluminescence The other really major group of photosynthetic organisms that descended from this Secondary endosymbiosis involving a red alga or what's called the strimenopiles And that name is not so important But it's basically a group that includes a huge diversity of different groups of organisms And several that are photosynthetic that we've long recognized as distinct groups But now it's clear that they're all very closely related. Whoops and one of these is the diatoms Which I just got I was just getting to at the end of last lecture and this is one of the most diverse groups Of algae there are over a hundred thousand species described And remember that's roughly the same diversity that we see across all of the fungal phyla So that's a huge number of taxa You know, it's it's roughly a third of what we've recognized among the flowering plants So it's a huge amount of diversity and you can see to get some sense of this diversity It's really clear morphologically that you're dealing with lots of different groups of organisms here And one of the reasons there's so many of them described a couple reasons. Well, one thing they're incredibly abundant You find them in huge numbers if you just take a scoop of seawater or lake water in different aquatic settings or marine settings You can find large numbers of diatoms typically and a lot of diversity But they also are morphologically differentiated Oftentimes by their cell walls which you can see are really extensively ornamented and There are many different shapes and sizes of these things in terms of different taxa and these cell walls are really amazing because they're actually largely made up of Hydrated silica like glass And they preserve really well then in the fossil record. They're inert and we have an excellent fossil record of diatoms that goes way back and Paleobotanists that work in this group have lots of stories to tell from the fossil record usually really rich and pretty complete records There's also extensive deposits of diatomaceous earth. It's called That's really valuable its mind extensively where you find these deposits of diatom skeletons and used for filtrate And a wide variety of purposes, but there's one really huge Deposit down in Santa Barbara County near Lompoc if you're ever down in that area. They've been mining that for many decades and One of the most important things about diatoms is that they may account for up to 25% of The photosynthesis the primary productivity that's going on on earth so they're Pumping out a huge amount of oxygen. They're capturing a lot of co2 and They're considered to be one of the crucial organisms for maintaining Atmospheric co2 at a reasonable level So there have been proposals to actually try to increase the number of diatoms in the ocean by dumping large amounts of iron into the ocean but so far that hasn't happened because these major types of ecosystem interventions like that sometimes have unforeseen consequences and it's not quite clear what that might end up resulting in You know the negative impacts might outweigh the positive ones but one of the things that diatoms do that's important in addition to fixing Co2 is that when they die they tend to sink and so they actually end up on the ocean floor and By doing that they take that carbon out of the ecosystem essentially and so that carbons not recirculating back into the atmosphere and So they can really store a lot of they can take carbon out of the system, which would be a really valuable thing right now Okay, and one of the strangest things about these guys is that these are unicellular typically Sometimes they'll be in filaments, but they're separate cells separate organisms And as you can maybe make out here not very well they they're So all is basically like two halves of a Petri dish with one half inside the other one and So when they actually go to reproduce it's pretty bizarre But I should mention first of all that they actually have an animal-like life cycle in terms of the type of well that the fact that there's only the only haploid stage is the gametes So they're just like us that way the mature diatoms diploid and they have Basically fertilization happens right after meiosis like it does with us So that's an interesting difference from other groups they also Reproduced by semi-conservative replication in a sense. It's almost like DNA replication that says that they're Each half of their shell they mostly asexually reproduce without sex mostly but when they asexually reproduce the two halves of the shell separate and A new half for each one of those halves is created inside the old one So if you're creating new shells inside the old half all the time at least some of the lineages are going to get to be progressively smaller through time and That decrease in size of course is going to reach a critical threshold at some point and Roughly around that time These lineages are stimulated to start producing gametes and they undergo sexual reproduction when they get too small and They release their gametes the two halves of the shell separate Release the gametes which have been produced of course by meiosis because they're diploid adult organisms The gametes get together with those of other individuals make a zygote and then that develops into a new diploid Fully-sized diatom So that's one of the really interesting things about diatom reproduction Okay, so there any questions about diatoms? Yeah Well a diatomaceous earth is used industrially for lots of different purposes It's an abrasive it can be used as an abrasive. I mean it is you know silica is involved and it's also Well, there's yeah, it goes on and on but it's used as a filtrate the diatoms have you know, they're so tiny and There's some porosity to their skeletons. I mean to their cell walls So it's yeah, there's a wide range of uses but yeah It's harvested on a mass scale. I mean it's mined on a large scale Or a number of different industrial uses Okay, so the diatoms are just one group of stromenopiles that one clade I mentioned That has quite a few photosynthetic organisms in it Another one of the golden algae and these are also unicellular or colonial but they're mostly in fresh water Diatoms are either fresh or seawater But they're called golden. I just want to mention because they have this golden appearance because they have these These accessory pigments in their plastids in addition to chlorophyll That are useful for capturing light at wavelengths that penetrate water well And that's something that we also see in their close relatives the brown algae Which are mostly marine almost all of them are found in the ocean and They also have this Yellowish or brownish color from these accessory pigments Well, it used to be thought that these were pretty closely related To land plants because they have pretty similar morphology and some of them have similar life cycles But now we know that these are actually a completely distinct lineage of eukaryotes that have captured Plastids, you know, they they descend from a common ancestor with the diatoms The gold ends and even the dinoflagellates that captured a red alga that have an ancestor that captured a red alga They don't descend from the green algal lineage And this includes some of our really Significance and large kelps We find these worldwide but off our coast we have some of the most most spectacular members that Both in the intertidal region up in the waves the wave crashing zone As well as out in deep water So up in the intertidal zone if you've been out along our coast just north coast In some of the roughest Areas of the intertidal zone where the waves are constantly breaking against rocks You might have seen these things look like little palm trees out there This is the sea palm. It's called Postell'sia palmiformis, which is actually edible. I've eaten this it's pretty good But it's only harvested on a low on a minor scale But it demonstrates first that some of the features of kelps that look very much like that of land plants First of all, look at this thing. It looks very tree-like. It has blades up here That are highly packed with plastids where you get a lot of photosynthesis occurring They look very much like leaves of a flowering plant. That's convergent evolution. There's no close relationship They also have a stem-like stipe or stock here That looks very stem-like, but that's completely convergent as well And they have a holdfast that affixes them to the substrate and that's also They look root-like, but that's not what that is. It's basically an attachment structure rather than a conducting structure And these things can withstand waves crashing against them that would tear any or any other upright organism apart And various biomechanisms that have been interested in the way that organisms can survive in this zone Where you have the waves crashing against them constantly You can't really easily account for these guys because they break all the rules And they shouldn't be able to withstand these impacts But one of the things that's important in this regard is that there are cell walls that are bathed in this gel-like polysaccharide So it's kind of musilaginous polysaccharide Which is found across the brown algae and also it will show later in the red algae as well, although it's different biochemically there But these musilaginous polysaccharides give this thing a lot of flexibility and strength It's one of the more interesting intertidal organisms But out at the other end of the spectrum we get these kelps growing in water up to 200 feet deep So in really deep water, here you can see one of our coastal forests of kelp And these are keystone organisms ecologically They provide basically a forest-like environment out in the ocean that provides cover You know, nursery ground, a feeding area for a wide variety of vertebrates and invertebrates So these kelp forests we have off our coast are basically our fundamental elements of this unusual ecosystem we have here along our Pacific coast And a lot of these big kelps that are out in deep water, they have floats near their blades that serve to buoy their leaves They're blades up in the upper water layers where they're more in closer proximity to where they have more availability to light So they have a number of interesting adaptations that were a number of different kinds of environments And they're a really diverse group both on our coast and elsewhere Okay, so those are the brown algae So the red algae, you're probably familiar with these too They often wash up on the beach just like the browns And we can find them from the intertidal zone down into much deeper water than where we find the brown algae These guys can get into water that's almost a thousand feet deep and where light can barely penetrate So these are really extraordinary in terms of their ecological range in the ocean And we find the most diversity of these ones in the tropical oceans But they're also well represented along our coast and we have a lot of diversity They have incredibly complex life cycles and we won't even attempt to try to teach you the life cycles of red algae Because they have various stages, they're real brain teasers as far as trying to figure out how it all works But there's bizarre things that happen, there's some red algae that actually will parasitize other red algae They have strange ecology But as you get into deeper water up in the shallow water, they tend to be more greenish in coloration Like the Nori that you're probably familiar with from Sushi Porfira, which is harvested from shallow water and is used to wrap sushi in Japanese cuisine But you get out into deeper water and they tend to be more reddish And there's a good reason for that, reddishness And that is that when you get out into deep water, here you can see the degree to which light penetrates in the ocean And breaking it out by the different colors of light And when you get down below about 125 meters in depth, you're pretty much just getting the penetration of blue and green light down here And so these are the wavelengths that these organisms can utilize when they're in the deeper water And so they tend to have accessory pigments that appear red because they're reflecting red light They're not absorbing red light, they're reflecting it They're absorbing blues and greens And these are ficoeretherans, the name's not important, but there are accessory pigments in the plastids along with the chlorophyll And they're masking the chlorophyll color Chlorophyll also has a high absorption in the blue end of the spectrum here But also in the red part of the spectrum, as you can see here The ficoeretherans have their absorption of light up in this area So they augment that and lead to a lot more photosynthesis than would occur otherwise at those deeper depths So that's what's going on with the red algae Okay, so finally now the green algae And we're going to basically be talking about green organisms for the rest of the course Are there any questions about any of the other groups we just talked about? Okay, so the green algae have a wide variety of different forms and ultra-structural morphological variation There's a number of different life cycles among the green algae, it's a really diverse group But these all seem to stem from that primary endosymbiosis that involved the capturing of the cyanobacterium And they descend from a common ancestor with the red algae that also diverged from that common ancestor That had acquired its photosynthetic ability from that primary endosymbiosis And they range from unicellular organisms like the clamidomonas, which is a model organism here You can see the two flagelli up at the apex of its cells here That's an SEM, it's actually green, it's just black and white And here you can see a colonial green alga, volvox These volvochalians are really cool, they move through the water as a big spherical colony And produce additional spherical daughter colonies inside The cells can live separately, but they can't reproduce separately So these are real true colonial organisms And then we have multicellular green algae like the sea lettuce here, ova One of the seaweeds, so there are seaweeds among the green algae too And they occur in both freshwater, I should say green algae occur in both freshwater and marine situations Different taxa, they also occur in high elevation snow fields And if you've been hiking up in the high Sierra during the summertime And you find, you see some snow field that looks red That's not some sort of air pollution or something that's caused that, or some sort of a pollutant But it's actually this organism, clamidomonas nevalis Which is a clamidomonas like these that has accessory red pigments And which is what we call cryophilic, it loves exceedingly cold water So it lives in the snow melt from the snow there So there's a huge ecological range in these things across the green algae that is Okay, so before going into the origin of land plants I just want to talk briefly about this major type of life cycle That has a nice representative in these guys, the ovas, the sea lettuces And it's also the type of life cycle we see in all the land plants, every one But it's been independently evolved in those two groups as I'll point out in a minute But Ova shows this type of life cycle well, so we'll talk about it in this context first So we've already talked about a comedic life cycle where the gamete is the only haploid stage Like in the case of us and the diatoms And we talked about a zygotic life cycle as in the fungi Where the zygote is the only diploid phase, the only diploid stage So in those two cases mitosis is only occurring in one of the two stages Whereas in an alternation of generations we have mitosis occurring in both the haploid stage and the diploid stage And that results in separate multicellular organisms that are haploid And that are diploid in the same species And these different multicellular organisms, haploid and diploid, are alternating generation after generation This is kind of a bizarre concept that you would actually have two different kinds of organisms in the same species That differ in their ploidy and their chromosome number And one of them, the gametophyte, which is the haploid organism, fight literally means plant Gametophyte refers to the gamete producing plant And since this is a haploid organism, gametophytes are always haploid That means they're going to be producing their gametes by mitosis, not meiosis like in us So we produce our gametes by meiosis Remember gametes are haploid, we're diploid, we have to produce our gametes by meiosis Which results in a reduction in the chromosome and having the genome content But gametophytes are already haploid, they germinate directly from spores, haploid spores And so mitosis produces gametes that are genetically identical to the parent gametophyte Those gametes fuse, of course, like any fertilization event And then we have a zygote, not shown here, but there'd be a zygote, of course And then that would undergo mitosis to give rise to what's called the sporophyte Which means literally the spore producing plant and it's diploid Sporophytes are always diploid, they always produce spores, not gametes Even though they're diploid, they don't produce gametes, they produce spores by meiosis But the important thing to not get confused about here We think of ourselves as diploid organisms undergo meiosis to produce gametes That's not what happens in land plants or in some of the green algae Meiosis gives rise to spores, and remember spores, unlike gametes, they don't fuse together with one another They just germinate to produce a new organism, which, of course, would be haploid after meiosis So that's the life cycle, we have this multicellular organism that's haploid As well as the multicellular organism that's diploid Any questions about that? Okay, let's look at an example now with OVA Oh, sorry, exactly, it's exactly the same as fertilization I didn't actually make this slide, it's from your book But if I'd written it, I would have written fertilization there because everybody knows that term But sin, gamete, just means fusion of gametes Sin just means fusion or fuse And gametes refers to the gametes They're synonymous terms Yeah, good point, this life cycle and its essence right here, this particular slide Is really an important one because this really boils it down to the essence of what the alternation of generations is The only thing that's not shown here that really should have been included was the zygote After sin, gamete, but I think just remember that after fertilization you get a zygote here But this is the life cycle we're going to be seeing the rest of the semester And it has various embellishments in different groups And so it's really important to get this down ASAP after the exam tonight Of course, I'm not going to, you know, probably don't want to cloud your mind with it right now But after the exam, you know, really get this down because, I mean in terms of these major components Because this is what we're going to be looking at from now on, okay So I just can't emphasize enough how important this is And the reason I want to show you an example in the sea lettuce, Ulva, is because this is one of the simplest alternation of generations that there is Essentially exactly like that other slide I just showed you And why I say it's simple is because it's what we call an isomorphic alternation of generations Where the sporophyte and the gametophyte look identical Isomorphic, iso means the same morphic, the same morphology for both the sporophyte and the gametophyte So we have the sporophyte here giving rise through meiosis to zoospores These are actually motile spores, but they don't fuse together, they're not gametes They just undergo mitosis and end up developing into a haploid gametophyte The haploid gametophyte produces haploid gametes by mitosis These are genetically identical to the haploid gametophyte And then they fuse together to produce zygote And that zygote then after mitosis and development becomes the diploid sporophyte So the only way to really tell these apart is if you did a chromosome count And you can see that this has twice as many chromosomes as this does, these two generations Also if you looked at their reproductive structures, this is producing sporangia Which are hollow sacs that produce spores by definition And this gametophyte produces gametangia, which are basically hollow sacs that produce gametes So that's the real difference, but there's not a whole lot to go on there So this is a really beautiful case of an alternation of generations where the two phases of the life cycle We call it the dip, the sporophyte or diploid phase And the gametophyte or haploid phase are very, very similar Yeah, these are free living from one another, but that's a really good point Because we'll see later in the land plants that it's often the case that the gametophyte Or the sporophyte is dependent on its immediate parent So we'll see parasitism by one generation on another generation in a lot of cases Okay, so as far as economic importance of algae, I've already mentioned diatoms and diatomaceous earth But there's some really important compounds that are harvested from brown algae and red algae in particular And I thought they were worth mentioning, already mentioned, well there are a large number of different Red and brown algae that are harvested as edible seaweeds used extensively in Asian cuisine We can't really act, we can't digest those carbohydrates, but they're a good source of minerals, roughage, etc And also this is a red algae, actually, nori, the one you're probably the most familiar with But there are browns as well that are used in Japanese cuisine, for example Another compound harvested from red algae is agar And agar, of course, is used for microbial culturing and petri dishes This is our typical culturing medium in scientific studies of microbes and molecular biology And agarose, a refined product there is used in electrophoresis So if you're trying to separate out DNA molecules of different sizes Agarose is generally the medium that's used for gel electrophoresis For large fragments, not DNA sequencing where we use acrylamide But for larger fragments, agarose is often used So for microbiology and molecular biology, red algae have proven to be really important And then the brown algae are sources of things like polysaccharides These musilaginous polysaccharides like carrageenan and alginate that are used as thickening agents Or emulsifying agents in a wide variety of different kinds of drinks and foods You're constantly ingesting alginate and carrageenan in processed foods It's included in all kinds of things I mean even in beer, to stabilize the head of beers And a lot of beers that alginate is used It's put in ice cream to keep it from melting as quickly as it would otherwise I mean there's a lot of uses that span much of what we take for granted in our food That comes from brown algae And here you can see an example in the medical profession of alginate being used As the main medium for dental impressions So these are really important substances that are used in a lot of different ways Okay, so now we're going to get into the origin of land plants And this bag weighs directly from algae Because the green algae, as you can see from this tree here, here are the land plants The green algae are a para-filetic group So the green algae don't form a clade by themselves Some green algae, an example shown here, are more closely related to land plants Than they are to other green algae So the sea lettuce and some of these marine algae, or the marine algae in general Are pretty distantly related to land plants And the closest relatives of land plants turn out to be freshwater algae Freshwater green algae So the most important point from these results, which come both from morphological data Mostly ultra-structural characters, really, you can't see with your naked eye And molecular data is that the land plants evolve from freshwater habitats So this conception of plants having invaded land from the ocean is misconstrued Based on at least the modern diversity All of the green algae that we know of that fall out in this clade That's sister to the land plants occur in freshwater So the ancestor of land plants had to first invade freshwater in the continental setting And then from there they invaded terrestrial habitats And it makes a lot of sense, I mean that sort of transition would make ecological sense And this is something that's pretty well established Now with the molecular data is available People have gone in and looked at the morphology more closely And there's a whole list of features that are in your textbook You can look it up if you'd like One of the most interesting ones I'll get to that in a moment actually But anyways, the thing that's come out of this is that We really can't have a phylum called green algae It doesn't work since they're paraphyletic The land plants appear to be monophiletic And these freshwater green algae that are close relatives are monophiletic These taken together are monophiletic groups Sometimes called the streptophytes And all of the green plants, all the green organisms now Are often referred to by botanists as the green plants So the green algae plus the land plants together They make up one big monophiletic group of green organisms And that's what you'll often see referred to as the green plants or virida plantae Okay, so there are questions about that Here's one of those... Oh, sorry, so here we go on to land And here's one of those freshwater green algae This is the genus Cara that the phylum is named for The Cara fites that are the closest relatives of land plants like mosses Again, freshwater These have a life cycle that is not an alternation of generations These Cara fites, the only diploid stage in these Cara fites is the zygote So they're more like fungi in that sense They undergo meiosis immediately after fertilization So the alternation of generations was not present in the aquatic ancestors of land plants But it's something that appears to have evolved subsequently But we have an alternation of generations in all the land plants like the mosses Okay, so that's an important point to consider And these Cara fites include unicellular as well as multicellular things like this So the multicellular condition may be independently derived as well in the land plants The alternation of generations that we see in something like Olva, the sea lettuce Probably evolved separately So the alternation of generations we see in land plants is probably of separate origin And you can see it, I'll show you as we go through here that we have a really nice progression In the evolution of the sporophyte generation So basically the main adult body of a Cara fite was haploid And what we see in the mosses and the other plants we call bryophytes Which are this part of the tree of land plants These are all the land plants here The bryophytes here, their main vegetative body that's photosynthetic Or the main photosynthesis at least that goes on in them Is the gametophyte, is the haploid generation And the diploid phase is very reduced Or I shouldn't say it's reduced, it's very small These things probably, land plants evolved from an ancestor that probably lacked any sporophyte phase, a diploid phase And so we see very small little sporophytes in these And what we'll see as we go through here is that the sporophyte gets progressively more complex And important in the life cycle, that's a theme in the land plants That we start out with the gametophyte, the haploid generation being dominant And eventually the diploid sporophyte generation becomes dominant in the vascular plants Which are the plants that we see mostly around us that are big and have major conducting tissue So the bryophytes include the mosses, the horn warts, and the liver warts And the ending wart, W-R-T, just means herb It doesn't mean some sort of, some sort of, you know, little carbuncle or something on these things These things have, wart is just an old English term for herb as opposed to a woody plant Okay, so there are three major groups of bryophytes as they're called And the bryophytes appear to be paraffyletic Okay, we're just seeing how the green algae look paraffyletic relative to the land plants The bryophytes are paraffyletic relative to the vascular plants Okay, the vascular plants include the ferns, the, all the seed plants The club mosses and spike mosses and clove warts These are basically all the really conspicuous plants that you see out in the environment And the mosses, the horn warts and liver warts are very small plants They rarely get over 15 centimeters in height, you know, something like that And that's because they don't have the sort of highly reinforced conducting tissue That allows them to retain large sizes But there are, anyways, there are three distinct groups That had already started to diversify into these major lineages Before the vascular plants originated And we could really say essentially that the bryophytes gave rise to the vascular plants These larger plants that have conducting tissue Given that they constitute a grade or a paraffyletic group within which the vascular plants are nested Any questions about that? Yeah, Brad? Yeah, the liver warts, I should say The mosses actually do have some conducting tissue And they're the only members of this group that can get fairly sizable There are in fact some mosses that can get up to a couple meters in height And they have what are called leptoids and hydroids That's not important, but they have some conducting cells That move around water as well as nutrients in their tissues But it isn't reinforced by lignin Which is the case in what we see in the vascular tissue of vascular plants And lignin imparts great strength to the conducting tissue In particular to the xyle on the water conducting tissue And allows vascular plants to be large branched sporefites To have large branched sporefites Horn warts and liver warts don't have those leptoids and hydroids And they're pretty much, as I'll show you here Let's go to the life cycle first of bryophytes to make this point And I'm not so sure I'm going to be able to get through the life cycle of bryophytes in three minutes or two minutes But I just want to make the point first and we'll get back to this next time That as I was saying, the gametophyte, the haploid phase Of bryophytes is the green photosynthetic dominant phase And you can see a typical moss gametophyte right here And again, it's germinating from spores It has a filamentous form early in its development And then gets to be more of a leafy stem But this is a gametophyte, not a sporeophyte So the structures that look like leaves are not truly homologous to the leaves We see in land plants that are in the sporeophyte generation But in any case, this is a gametophyte And then it produces gametangia up in the tips here And we'll get to those gametangia later But basically the sporeophyte is just the structure here It's parasitic on the gametophyte, it grows out of it And it's pretty much just a sporangium on a stalk So we have a highly reduced, or I should say a small sporeophyte Where we have meiosis giving rice to spores So this is just an intro to the briophyte life cycle We'll talk more about it next time So remember to set your clocks back again And good luck on the exam tonight