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Plant Reproduction

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Plant reproduction is the creation of new offspring through asexual or sexual reproduction. In plant reproduction, flowers attract pollinators. In flowers, the stamen are the male parts while the pistil or the female parts. A plant seed protects and feeds the plant embryo. The main parts of the seed are the seed coat which protects the seed, the endosperm which stores food, the cotyledon which is the seed leaf and the hypocotyl with is the seed stem.

In the plant kingdom there's many different reproductive strategies, but the experts at reproduction is the angiosperms, the flowering plants. So let's take a look at the flower that gives them their name and see what it is that allows them to be so successful.
So when you take a look at a flower, you're actually looking at a structure that's designed to attract some animal, who will come along, pick up the pollen from one flower of a particular species and bring that pollen to a flower of the exact same species and transfer that pollen to that other flower. Thus allowing two different plants to have essentially, have sex with each other. When you look at a flower, it'll typically be hermaphroditic or it'll have both male parts and female parts. We refer to the male parts as the stamen and here we see this yellow thing with the green guy holding it up, that is a stamen. The yellow part on top is called the anther, the long green stalk that holds it up is called the filament.
Now, how can you remember this? Well just remember, males usually 'stay men' and we males think we have all the 'anthers' alright? Now the female parts are collectively called the pistil. They include several different regions. You'll have the stigma on top of this long stalk which is called the style. Down at the base of that you'll have the ovaries. Now one ovary plus its portion of the style and its portion of the stigma is called the carpel. Now how can you remember some of these terms? Well, one way that I tell my students is just remember; females have 'style' but that carries a 'stigma.' Now another thing that is kind of a stereotype, so I'll warn you about it but, how can you remember that an ovary plus a style plus a stigma that's a carpel well, the stereotypes of females is they form carpools... couples... that one kind of sucks but oh well.
So the basic way that this works is that the anthers, the part of the flower that produces the pollen grains; those are the essentially the male sons called the gametophytes. You may have gametophytes of this flower. They get picked up by wind, they get picked up by a bee, they're picked up by some kind of animal. And they get carried to another flower where it lands on the stigma, that is sticky so that the pollen will attach to it. And using various chemicals, you'll recognize that it's at the right stigma. And then part of the pollen grain will actually eat a tube all the way down, to the inside of the ovaries where you'll find the ovules. This is the chamber where the egg is produced that'll grow into the female gametophyte, the daughter of the flower.
The sperm cell will go down that tube that got eaten by the tube cell and will fertilize the female gametophytes egg and that's how you can make the seed, that seed grows up ultimately to form the seed that you see here. Now there are several major parts of the seed. There's the seed coat. That's a thick layer that prevents the seed from being dried out. The endosperm is the storage around the seed, around the internal portion of the embryo and that's just a big storage of food to help feed it, when it gets ready to germinate. You'll see these two long things here if it's a dicotyledon. You'll see one if it's a monocotyledon.
These are the cotyledons as you may have guessed from the one or two, mono and dicotyledon. And these are the leaves that will be used by the growing seed or growing embryo as it first breaks through the dirt and it starts to do photosynthesis. They're often will also be kind of thicker and have some stored up food in them. Down here you have what's called the hypocotyl which literally means below the cotyledon. And this is the seed stem. So that when it starts to grow initially the hypocoto will push its way up through the dirt and then lift the cotyledons up and start to do photosynthesis and grow. And that's how plants reproduce.