What are Angiosperms?
are some of the most successful and also most diverse plants around.
When you think of flowering plants, you may not realize that a lot of plants actually
produce flowers. Many grasses for example. Many crops. All plants that produce fruit.
In fact, flowering plants all bear fruit---just maybe not fruit in the sense that you are
used to. Not all fruit ---if going by the biological definition---are sweet or even edible.
By the biological definition, a fruit develops from the ovary of a plant. Which doesn’t
exactly sound that appetizing.
Pumpkins, green beans, tomatoes---these
all developed from the ovary of a flowering plant. These are all fruits.
The term “vegetable” really isn’t
used as a true biology definition. A lot of what grocery stores classify to be vegetables
are other parts of plants----like leaves (think of lettuce) or stems (think of celery).
and sometimes grocery stores just classify vegetables as plant structures
that are generally not as sweet.
So angiosperms have flowers and these are the reproductive structures. Many flowers
contain both male and female parts. Other remaining flowers only contain one gender of parts.
Let’s talk about flower parts of angiosperms. First, we’ll start with male parts. The
male parts make up the stamen. Stamen has “men” in it so that helps me remember
male. The stamen have the filament and the anther. The filament is a stalk-like that supports
the anther---the anther is a rather fluffy structure that produces pollen. Really---pollen
is the sperm of the plant.
now onto female parts: the pistil. The pistil is made of three major parts. The stigma---I
The style, which is the stalk that supports the stigma, and then the ovary at the base of
this structure. The ovary is where fertilization occurs. The
also remember the ovary will ripen into fruit. There are some parts of the flower that are
neither male nor female. Sepals for example. Sepals protect a developing flower bud. Or
petals for example. Fancy structures that help attract pollinators. Which will take
us to my bee story and also the steps of angiosperm (aka flowering plants) reproduction.
First, let’s understand a pollinator, such as the bee. Pollinators can include many
types of organisms - hummingbirds, butterflies, and bees are all examples
while pollen contains amino acids that some pollinators may feed on,
and bees certainly do use the pollen as a food source, especially for their young, another great attracting factor
for many pollinators is nectar
nectar is a sugary sweet substance produced by many flowering plants
and it is a great source of carbohydrate, meaning a great source of energy
as a pollinator which can drinks the sweet nectar,
some of the sweet nectar, they tend to brush against the anthers of a flower. remember that anthers produce
pollen. Have you ever gotten a really good look at a bee? Many times you will see a yellow
dust---pollen---all over their bodies. They just can’t help themselves…
The idea is if this pollen can be brushed from a pollinator onto the sticky stigma, the flower
can be what we consider pollinated. But it’s not done yet. Pollination is not enough.
the sperm cell must join an egg to be fertilized. And if it's just sitting there on the stigma,
it hasn't gotten there yet. just a disclaimer, we are going to
simplify this amazingly complex process of fertilization in angiosperms. but understand the main function is that
this process is going to help the plant develop seeds, which can then grow into new baby plants
first, you have to understand that pollen grains, well, mature ones anyway, consists of two types of cells.
a tube cell, and a generative cell. so basically this pollen grain, once landing on the sticky stigma,
through the style to the inside area of the ovary
the generative cell, which is enclosed in the tube cell,
will divide to form two sperm cells
so, what would these two sperm cells want to do?
well they are actually going to target the ovule, which is inside the ovary
they're going to be multiple ovules inside a plant ovary
but each ovule has a seed if fertilized
now the ovules have 2 major key players to mention
an egg cell, and something else called 2 polar nuclei, which I'll get to in a second
one of the sperm cells fertilizes the egg, this forms a zygote which is a basically a fertilized egg
the second sperm cell joins with two polar nuclei
the function of combining with these 2 nuclei is that this will develop into the endosperm.
in here too---this is very important because this will develop into the endosperm.
now if you are wondering how did the egg cell develop and where did the polar nuclei come from,
a highly encourage doing a little research. it's a process we need another video clip to cover
because the fertilization process involves sperm cells joining two different things, (the egg and the polar nuclei),
we call this double fertilization. double fertilization is an important event in angiosperms.
Angiosperms have this added benefit that the ovary will ripen and develop into a fruit
(remember: not necessarily an edible one) they can help seeds travel far from the parent plant
you don't want baby plants to have to compete with their parent plant
for the non-edible fruits, some have the ability to stick to animal fur or be carried by wind or water
for the edible fruits, when an animal eats them, the seeds may pass through the digestive system unharmed
but in this way they can travel a great distance from the parent plant.
One thing to point out that we didn’t mention in our example--- many species of angiosperms
are picky and will only accept pollen from another plant and not accept pollen from their
own anthers. (Basically not allowing self pollination). Which would make the travel
of pollinators even more important. For crops all over the world----what would we do without
our pollinators? wind and other methods can only take you so far. because pollinators are so important,
we found a bee keeper who happily relocated our bees and took them off to a bee farm where they could happily pollinate flowers.
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