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Hello students, this is non-flowering plants and nevertheless we are going
to cover The Angiosperm Lifecycle, the flowering plant lifecycle.
So let's go through the overview here.
We have seeds.
Now the seeds in angiosperms are little bit special in addition
to the embryo we have another tissue outside of the tissue called the endosperm which is made
by the confluence of male and female contributions from the mother
and father but it's not part of the embryo.
That is inside of the seed.
Seeds are dispersed as usual.
They grow up to be sporophytes and then they make flowers.
The flowers have some special structures that we will get into.
One of the special structures is the carpel and that is a structure
that encloses the ovules then ultimately the seeds.
So we have ovules there.
Then the same flower or other flowers makes pollen grains
and then pollen grains during pollination are transferred to the carpels,
usually of a different flower when they are successful.
Then the pollen grains germinate, they grow pollen tube and fertilization proceeds,
both fertilization that makes the embryo and fertilization that makes the endosperm.
So let's go into it in more detail.
Here we start with the seed.
That seed disperses, it makes a little seedling, that seedling then grows up to make sporophyte
and that sporophyte then would have flowers.
Now the flowers could be showy flowers or they could be flowers that are pollinated
by the wind, for instance grasses are flowering plants and they have flowers.
Nut trees are flowering plants and they have flowers, but those flowers are kind
of small whereas tulips have flowers and tulips have larger flowers.
For many flowering plants the flowers have four whirls of structures.
The outer whirl is a whirl of sepals and there is a whirl of petals.
The next whirl in is the male whirl and it consists of a series of stamens,
and then the central whirl is a whirl of carpels.
The carpels will have ovules inside of them.
Here's a blowup of the ovules.
It has two intagumens on the outside, then there is the nusales,
and there's of course a micropile but there's no pollination drop in these things.
Then in the center there is a mega spore site
and that mega spore site undergoes meiosis and makes more mega spores.
Three of those mega spores whither and that leaves functional mega spore.
That functional mega spore undergoes a few mitotic divisions
and it makes a female gametophyte.
A mega gametophyte.
And that mega gametophyte we call an embryo sac.
So in this case that's diagramed, we have an embryo sac that consists
of three antipetal cells, an endosperm mother cell that has two nuclei called polar nuclei,
an egg and then a synergid cell on either side of the egg.
That's the mega gametophyte or embryo sac.
Okay, let's go back and look at the male structure, so we have stamens,
at the top of stamens are anthers.
Those anthers have a series of microsporangia, four in this case.
The microsporangia contain within them microsporocytes,
the microsporocytes undergo meiosis and make microspores,
those microspores will then divide a couple times and make pollen grains.
So pollen grains are micro gametophytes.
Those pollen grains will consist of a couple of cells that you can see,
a generative cell and a tube cell.
You can usually see both of those and then those pollen grains will be dispersed
during pollination.
Pollination could happen by insects or by humming birds or by bats or by winds.
Lots of different types of pollination.
Pollination is the movement of pollen grains from the stamens that produce them
to stigmas often of flowers of a different plant.
And then the pollen grains germinate and they grow a pollen tube.
That pollen tube will have two *** nuclei inside of it.
It will then get to the egg, and fertilize the egg and that makes a zygote
and then the other *** nucleus in this case fuses with the polar nuclei
of the endosperm mother cell to make endosperm.
In this case endosperm is a triplet tissue, its nutritive, it grows around the embryo.
In other flowering plants the endosperm could be of a different [inaudible].
So we end up with an immature seed that matures.
It's inside of an immature fruit that then matures.
Inside of the seed coat we have endosperm and then inside of that we have an embryo.
So I have made this little poem for you.
The poem reads: Eggs plus *** make zygotes that grow up to be embryos.
Polar nuclei plus the other *** nucleus grow up to be endosperm.
Ovules plus *** result in immature seed that grow up to be seeds.
And then the carpel after fertilization is an immature fruit which grows up to be a fruit.
And a fruit can be something that is dispersed by birds, and it's fleshy,
or it could be something that has wings, and disperses the seeds that way.
Or it could be something that opens up and releases the seeds and then seeds disperse
but the carpel wall, the fruit remains on the mother plant.
And that's all that I have to say about that.
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