Angiosperm Reproduction: Flower Structure, Pollination, and Seed Development

welcome back to our series on plant diversity and evolution this is part two in our section on reproduction of seed

plants we'll look at the angiosperms the flowering plants in this video we'll look at the parts of the flower pollen

development egg development pollination fertilization seed development and finally fruit development so let's get

to it we'll start with parts of the flower when we look at the flower we see down here we have the seil

these were covering the flower when it was just a bud protecting it the growing bud we have the petals we'll talk about

the function of petals later we have the anther and the filament which together make the stam now this is the male

structure of a flower it's where pollen's produced in the middle we have this vase likee

structure and at top of which is called the stigma the long thin neck is called the style and the bottom the swollen

part is the ovary together these three parts make up the carpal and this is the female part of the flower now what I've

drawn here is What's generically called the perfect flower it has both male and female parts some flowers might only

have the female structures and other flowers only the male structures but uh to simplify I've just kind of done a

generic flower here we'll look at the male side first with pollen development in the

staman if we look inside the anther we see diploid cells remember when you're looking at a flowering plant you're

seeing the sporify generation or the diploid generation these cells inside the anther are called microspore mother

cells they're not spores they're the Mother cell to spores specifically the microspores so to become a haid Spore we

have to undergo meosis and inside the anther then we build

microspores now if we recall our alternation generation life cycles which is the basis of all plant life cycles

spores will become the gamify generation so these spores will grow by mitosis to form pollen grains remembering that the

pollen grain is the male gapy in flowering plants in seed plants so if we blow one of these up and look closer

here's the male gimit toy or the pollen inside the pollen there are two distinct cells the tube cell and the generative

cell the tube cell will make a tube through the style to the ovary to a INF fertilization we'll look at that shortly

and the generative cell will generate the sperm cells so this is the gapy this is not the male gamt pollen is not tree

uh sperm it is the gight but it will be transferred from one uh plant to the other so here's a look at the whole

process of pollen development inside the anther the microspore Mother cell undergoing meosis to make the HAPO

microspores the microspores developing into the pollen grain all that happening in the staman now

let's get back to our flower now let's look at what's happening on the female side of things inside the

carpal if we zoom in if we could look inside the ovary we would see many structures sometimes more than one

sometimes just one these structures are egg producing structures they're called ovules so inside the ovary there are

ovules now for Simplicity sake I'm just going to draw what happens in one OV so in an U inside the ovary again

there's a diploid cell this is the sporify generation this is the megaspore Mother cell it's going to give rise to

the megaspore so this diploid cell undergoes meosis forming Hao megaspores now most of the time all the

megaspores except for one disintegrate so only one megaspore survives so there's our one megaspore

the Spore will become the gight so it'll divide and it goes through three rounds of mitotic division so three nuclear

divisions so our one nuclei becomes two and the two become four and the four become eight and then something very

interesting happens these eight nuclei are divided into their own cell through cyto canis but we only have seven cells

formed pause the video and think about what that means draw what it might look like like we have eight nuclei but only

seven cells how about something like this this is what it looks like this is the female

Gita fight now when we look in here let's see what we see we have this cell which I've

drawn in a different color to make it easy to see but that's the egg one of these haid nuclei will be the egg we

have this special cell that has two haid nuclei in it and it's the endos sperm Mother cell it will give rise to the in

the sperm it's an N plus n cell and then these other five cells these other five haid cells we call them snid which is

one of my favorite words they're unimportant cells they're going to disintegrate these two included but I

want to draw my arrows all over the place but the snid so we have this structure inside the ovil so here's the

whole side of the female uh reproductive structures of egg development so the megas

a Mother cell becomes a megaspore one of them survives and divides to make this structure inside the OVU prepared for uh

the sperm so we have pollen made in the anther and the eggs are ready inside the

ovule so what do we need next we need pollination we have to get the pollen from a uh an anther to a stigma

well how can that happen well wind a lot of pollen is wind born and even water water can move pollen but what do we

think about when we think about flowers and angiosperms the thing that's unique and different between angiosperms and

gymnosperms is the use of yeah biotic vectors which is a fancy way of saying pollinators living things that move

pollen from one now it's time to answer a question what is the evolutionary significance of petals nectar the

fragrance of flowers pause the video and answer the question to attract pollinators now

think about how important pollinators are to angiosperms in fact there's been a co-evolution of flowers and uh animals

to uh ensure or Aid this process of um the plant providing some nutritional value to the animals and the animals in

turn moving the pollen from one flower to another to Aid in reproduction okay so here comes the

pollen lands on the stigma pollination once we have this we're ready for the next step

fertilization and we're going to zoom in again to the uh caral and here I put the pollen grain on top of it we can see the

tube cell and the generative cell and we're ready for the process of fertilization we have our egg but we

don't have our sperm we have pollen so this is what happens the tube cell is going to create

a tube down through the style to the ovary then the generative cell is going to generate two sperm that travel down

the tube when they get here they're going to have a double fertilization

event one of the sperm is going to fuse with the egg to make the zygote The second sperm is going to fuse with the

endosperm Mother cell to make a tripid cell that's going to be beginning of our endosperm our nutritive

tissue since there are two Fusion events we call this double fertilization this is different between the gymnosperms and

angiosperms the gymnosperms we don't have this the nutritive ti tisue the endosperm is haid but in angiosperm

because of this unique uh n plus n cell the Nutri tissue is triploid and it's fertilized by one of the sperms so we

have double fertilization and what about all these snurds what happens to them well they

just go away so now inside our Avil we have the zygote and the growing endosperm and they're going to start to

grow and divide so now let's look at embryo and Seed development the zygote in the U starts dividing by

mitosis and the embryo has lobes of meristematic tissue called codin so we'll let the embryo start to

grow the nutritive tissue around it the endosperm is triploid by the time the embryo matures

the ovule becomes detached from the wall of the ovary its ingt start to thicken forming

the outer seed coat so the ovil is becoming the seed the embryo the endosperm the Nutri of

tissue surrounding it and the seed coat constitute the seed so the OVU is inside the ovary and the OVU becomes the seed

now these are angiosperms in the uh video where we introduced seed plants we defined what

anges sperm meant it means covered seed so here's a seed and it's covered by something but in that video what did we

say seeds were covered by write it down yes fruit so now we have to have

fruit development let's put this back into the flower and see how the fruit

develops well the ovary of the flower is going to start to swell and the Petals of the flower start to break down and

start to Fall Away the uh ovary continues to grow the ovary becomes the fruit ovules are inside of ovaries seeds

are inside of fruit and if the ovil becomes a seed the ovary becomes the fruit Sometimes some of the other parts

of the flower are incorporated into the fruit but there we have it the um the fruit is the mature ovary now

some fruits are fleshy and some are dry like acorns and pea pods but we have this

question what's the function of fruit pause the video and write down what you think the answer

is now a lot of students will say that the function of fruit is to protect the seed but hold on think about fruit

what's protective of a seed if the fruit encourages you to eat it think about

that and also think about other types of fruit anything with a seed inside of it is a fruit so pea pods the Pod itself is

the fruit and the peas are the seeds peanuts the peanut this is a a fruit by definition and inside are seeds and we

have seeds like all the nuts are B are are fruit um they're not the seed the seed is

inside there and think about fruits like this these little sand spur that get on your shoelaces when you walk down by the

beach or these which if you were an animal would catch into your fur and pull off this is a fruit this is a fruit

and what about this each of these little dandelion things that fly off caught by the wind this is a fruit inside of that

little pod right there is a seed so what's the function of fruit to Aid in seed

dispersal to be caught by the wind or to float in the water or to even be eaten by an animal go through the digestive

tract uh protected against the harsh enzymes and acids of the inest digestive system to be deposited somewhere else in

its own little pile of fertilizer it's the aid and seed dispersal which helps the plant survive

so the seeds uh um we talked about in the in the anent seed plant video having advantage of allowing us to move into a

broader range of environment but flowers and fruits have uh evolved to Aid in reproduction of plants and to spread the

seeds so that brings us to the end of our video on the antisperm reproduction if you have any questions leave them for

me in the comments section below the video and I hope you learn something