hi everybody and welcome back today we're going to be looking at gymnosperms which is our third installment in this series of videos please remember that in every video i will be recapping alternation of generations just so that you're familiar with the terminology before we move on to the rest of the video in which i then go into the life cycle of gymnosperms so let's get into exactly what are gymnosperms and what makes them so unique now this is the next step in plant evolution so they are very well developed for terrestrial life and i'm going to go through a list of things that makes them so well developed but one of the most defining things about gymnosperms is that they produce seeds up until this point we've only had spore formation we haven't had any seed formation now what makes a gymnosperm specifically a gymnosperm is that they create naked seeds which essentially means there's nothing that sits around their seed whereas angiosperms which is the next step in our plant evolution will have a seed that is covered in some kind of fruit now let's have a look at some characteristics around gymnosperms that make them unique so our gymnosperms have a very very well developed vascular tissue which means that xylem and phloem is very well developed and this allows gymnosperms to grow to the sizes that they do up until this point moss and ferns are very small delicate plants whereas our gymnosperms you think of them like pine trees they grow really really large and tall and that's because of their vascular tissue and that supports them the next thing that gymnosperms have that's really important for their terrestrial life is that they have quite a thick cuticle and also uh their leaves are quite needle-like and if we look at the diagram alongside the picture alongside you will see that their leaves um are quite uh thick they sort of remind you of a needle shape i'm just going to ring them so you can see them and and that is to reduce water loss it is also to prevent herbivores from eating our gymnosperms and to deter any kind of um possible um eating of our seeds and our codes because we want to avoid that as well which brings me to my next point is that they produce naked seeds and essentially what that means is the seeds are not inside any fruit that's not to say that we don't have anything protecting them which we do gymnosperms create cones and we can see some lovely examples of cones in the picture alongside they actually have male and female cones each providing a separate gamete and lastly they rely on wind pollination and so alongside plant diversity we also have animal diversity happening at the same time where we would then rely on different pollinators now at this point gymnosperms don't need pollinators they only rely on the wind which means they make lots and lots of pollen it's very light and it's easy to blow away but as we develop you'll see that our angiosperms in the next video they need pollinators to assist with pollination so once again let's recap alternation of generations and literally what that means is a plant is going to alternate between the generation it finds itself in it's either going to be a diploid generation which we refer to as the sporophyte or in this case we can say diploid is 2n and it alternates with its haploid generation which is the gametophyte generation and so the alternation between these two generations is what we see in our bryophytes and our geritophites and it's very clear in the two previous examples because they are two very separate structures in gymnosperms it's a little bit harder because when you look at a pine tree as an example you are looking at a diploid sporophyte so you're looking at the largest structure now in our gymnosperms and in our alternation of generations when you look at a pine tree you are going to see cones and in those cones we are going to find our sporangium and it's either going to be the mega sporangium or the microsporangium and our diplosporophyte has going to go through meiosis which if we remember meiosis is the process whereby we half a chromosomal number and so this happens in both male and female structures where we take a chromosome number of perhaps 20 and we're going to half it and it will become 10 in the haploid gametophyte generation so in this example in the picture let's say we took our microsporophyte which are our little teeny tiny cells that we can see inside our microsporangium it undergoes meiosis and it produces microspores each one of these microspores is haploid that then develops um and it produces sperm cells so we're going to take one of these little teeny tiny cells inside here we're going to make spoon on the female side of this cycle we have a mega sporophyte with our megro sporocytes in the inside of it undergoes meiosis yet again halfing and we end up with megaspores those megaspores are going to develop they're going to get a little bit bigger and they are going to produce an egg cell if we fuse a sperm and excel together we will produce a zygote and the whole process starts again now alternation of generations is a little bit less obvious in gymnosperms because there isn't two separate plant structures sometimes um it's a little bit difficult to imagine this but think of it like this where bryophytes and terenophytes had two separate plants that you could physically see with your eyes in gymnosperms i want you to think of the alternation of generations between the adult structure which is not reproducing and then the structures it grows so that it can reproduce and so when we say it alternates between generations it doesn't mean that the whole big plant dies and it's still alive it's just that on its leaves and at the ends of its branches it's growing it's going to grow and a structure that can grow its gametes for it which are its sperm and egg cells now let's get into the actual life cycle of our gymnosperms so what i'm going to do is i'm going to zoom in on where our journey is going to begin and because this is a gymnosperm gymnosperms spend the majority of their time in their sporophyte generation which means that they are going to spend the majority of the time as an adult as we can see here and so we're going to start our journey here at our mature sporophyte this is our pine tree it's important to remember that everyone on this side of the life cycle or this side of the generation is deployed which means it has a full set of chromosomes now on our mature sporophytes or a mature pine tree we are going to find male cones and we are going to find female cones and inside of these clones we are going to be able to produce our gametes and that's where we're going to find our gametophyte generation so inside of our female and male cones we are going to go through the process of meiosis which remember is when we go from a diploid set of chromosomes and that becomes a haploid set of chromosomes and where all of this takes place is deep within the cones themselves so let's start off with the male reproductive system because this one's a little bit easier so we'll start here with the male cone if we start with our male cone and we zoom in on one of the little tiny scales of the male cones it says each scale has a microsporangia now we've heard this word before it's the place where we are going to make microspores and so if we cut it open on the inside with this being our micro sporangium on the outside you can see sitting on the inside you have multiple micro spores and these microspores are going to become our pollen grains these pollen grains are really important because they are carrying our sperm cell on the inside so if you imagine it if this is our pollen grain sitting inside of our pollen grain if i just draw a very simple diagram is going to be our little sperm cell sitting inside of it so the pollen grain is a delivery mechanism it's the way in which we get the pollen to go in the direction we need it to go in now let's look at the female cone now the female cone is significantly bigger and her scales are also bigger and on the inside of each of her female scales we are going to find the mega sporangium and the megasporangia have what we call ovules on them which are these swollen areas over here and that is essentially what can become the seed if it's fertilized and so that on the inside is going to be growing a couple of structures so let's move over to the side now inside our just move this over there we go inside of our female reproductive system i'm going to zoom in just a little bit more okay we have a couple of important structures so on the very inside we have the mega sport growing the mega spore is going to become the egg it's not the egg yet it's getting there it will get there and it is housed inside the mega sporangium now whilst that is growing and developing it creates the female gametophyte so that's this entire thing if i were to put a circle all the way around it this whole thing is the female gametophyte now what is the male gametophyte well that is the pollen grain so now we know we have our gametophytes so what happens next well as you can see in the diagram our pollen grains are released and some pollen is going to land on our um the base of our little female cone in the scale i'm just coloring in here that's where the pollen grain is going to land over here and it's going to grow a pollen tube and the purpose of that pollen tube is so that our little sperm cell can swim and be mobile and get down to where it needs to go now if we move along in our development we are now going to move back into being diploid now the only way to do that is for us to go from um a haploid sperm cell and a haploid egg cell together they will form a diploid zygote and so this process is called fertilization when you take an egg cell plus a sperm cell and you make a zygote so if we do that with our lettering n plus n so sperm plus egg is going to equal our 2n or our diploid structure which is our zygote now in this diagram they are speaking about a second sperm cell and they're speaking about the fact that there is um another structure over here and what that will eventually become is a endosperm but i'm only going to speak about the endosperm in the next video under angiosperms so for more details watch that video on what this what the purpose is of the second sperm cell so now we have some fertilization inside the female cone she matures she bursts open and once she has done so there are going to be some seeds and remember these seeds are the zygotes they are waiting to develop into future adult sporophytes so it needs to grow and it needs to germinate and so what happens is if we were to cut one open we can see the seed coat on the outside and we've got the embryo on the inside remember that's the future baby tree and all this leftover female gametophyte is nutri uh is nutrients it's nutritive tissue that we would use to grow our future baby tree and that's essentially what that second sperm cell was for but like i said i'm going to clarify that again in our angiosperm video that then let's imagine that those seeds break off they fly in the wind and they land somewhere and now we have a newly germinating seedling that's in the ground it's growing and if we were to zoom out and bring everything back into focus we now have done the full life cycle of our gymnosperms we start all over again with a mature sporophyte and we start again so let's do a terminology recap so we looked at the fact that gymnosperms have lots of very well developed vascular tissue which makes them grow really big and it allows them to support their own body weight they have a very thick cuticle they have needle shaped leaves gymnosperms use wind pollination in order for their pollen to get from the male system to the female and these ultimately are going to produce seeds these seeds are naked which means they don't have any fleshy covering however we do find them inside of cones now we know that in alternation of generations we alternate between the sporophyte generation and the gametophyte generation in gymnosperms is a little bit harder to tell the difference between these two because they're not two separate plants the sporophyte generation in gymnosperms would be the adult pine tree or the adult plant and the gametophyte would be the pollen grains and it would be the developing archegonia inside the ovule inside our female cone someone's a little bit harder to find but it's definitely there and we also looked at diploid and haploid which are related to the sporophyte and gametophyte sporophytes are diploid which means they have a full set of chromosomes gametophytes are haploid which means they have half the set of chromosomes we then looked at how exactly do we actually make these diploid cells into haploid cells well in the male system in the male cone there is a microsporangium which produces microspores that are essentially pollen grains and in the female reproductive system we have mega sporangium which is where we eventually make the egg cells now pollen is the product at the very very end it's like a round capsule that has a sperm cell inside of it the ovule is the structure where we are going to grow our egg cell and eventually our seed a fertilization occurs and in order for fertilization to occur we learned about a pollen tube which is a thin little tube that will grow out of the pollen down into the ovule and it will allow the sperm cell to swim its way from the pollen grain into our awaiting egg and that's that's basically it for gymnosperms i hope that this video was helpful and please remember to use this for revision and i will see you all again very soon bye