Captioning is on. Click the CC button at bottom right to turn off. Today’s topic is the exciting process of
plant reproduction in angiosperms. But before we get into that, we want to tell you a little
story that completely relates---and always reminds us of how fascinating plant reproduction
really is. Now we are sisters that live in different
areas of Texas, with our own separate families. One day, in the Pinky household, I happened
to notice a few bees flying by our window. I happen to be pretty enthralled by most insects
so my family watched these bees for a while. It didn’t take long to realize that these
bees had made a nest---a beehive so to speak---in the insulation material in our house. They
had found a small opening through the window sill. Some people may not enjoy this, we realize- but we were a little fascinated. It’s not every day that you can observe a beehive so close.
But over the weeks, we found a lot of friends suddenly started having some weird plans and
things that came up that always seemed to keep them from being able to visit our house.
One day, we had a little family barbecue and learned a very scientific lesson.
(Not really). Bees do not like barbeque! Or maybe they don’t like the smoke from
the grill, we're not really sure. And maybe it was just that our particular bees had a distaste
for barbecue---we have not done a controlled study on this. But on this day, it became
apparent to us that the bees had to go. But we didn’t want to call an exterminator.
Why? Well that’s where we get into this amazing story of plant reproduction. We’ll
come back to this story in just a minute and how it ties into plant reproduction.
Angiosperms are flowering plants, and they are some of the most successful and 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 the type of fruit you are thinking of. 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 appetizing. Pumpkins, green
beans, tomatoes, squash---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 structures 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 flowers only contain one part. Let’s talk about flower parts of an angiosperm.
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 includes the filament and
the anther. The filament is a stalk that supports the anther---the anther is a rather fluffy
structure that produces pollen. Now on to female parts. The pistil. The pistil is made of three major parts. The stigma---I like to say “sticky stigma” because pollen
is supposed to stick onto this sticky structure. 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 will occur inside and seeds are formed within it. Also remember that the ovary will ripen into a 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. 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 do certainly 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 carbohydrates- meaning a great source of energy! As a pollinator drinks 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- consist of two types of cells. A tube cell and a generative cell. So basically this pollen grain, once landing on the sticky stigma uses the tube cell to burrow down a pollen tube from the stigma through the style to the inside area of the ovary. The generative cell will divide to form two sperm cells. So, what do these two sperm cells want to do? Well, they are actually going to target an ovule, which is inside the ovary. There can be multiple ovules inside a plant ovary. But each ovule has the potential to develop into a seed if fertilized. Now the ovules have two major key players to mention. An egg cell and something else called two polar nuclei, which I'll get to in a second. One of the sperm cells fertilizes the egg. This forms a zygote which is basically a fertilized egg. The second sperm cell joins
with the two polar nuclei. The function of combining with these two polar nuclei is that this will develop into the endosperm. The endosperm is full of nutrients for a developing
baby plant. Now if you are wondering, how did the egg cell develop and where did the polar nuclei come from? I 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 also have an added benefit that the surrounding ovary will ripen and develop into a fruit (remember: not necessarily an
edible fruit) that 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 nonedible 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
other plants 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 beekeeper who happily relocated our bees and took them off to a
bee farm where they could happily pollinate flowers and let us barbecue at our house in
peace. Well that's it for The Amoeba Sisters, and we remind you to stay curious!