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  • Hi. It's Mr. Andersen and in this podcast I'm going to talk about plant

  • structure. So a good way to think about this is plant anatomy. If you never stood next

  • to a giant sequoia then you should. It dwarfs all the trees around iy. And it shows you

  • how huge plants can become. Just using a few simple ingredients like water, carbon dioxide

  • and a few nutrients from the soil it can become massive. And you can see the rings that we'll

  • talk about kind of near the end. And so basically everything I'm going to talk about for the

  • most part is going to be angiosperms. So flowering plants. And flowering plants can be broken

  • down into two different dicots and monocots. And so what is a cot? A cot is simply a cotyledon.

  • And so a cotyledon is going to be a baby plant leaf. And so here we've got two different

  • seed types. There's going to be a seed coat around the outside. And little endosperm in

  • here. But you can see this baby plant. And in this dicot you'll have two cotyledons.

  • One, two. But in a monocot you're only going to have one. Now the quintessential dicot

  • that I think of is dandelion. And a monocot I think about is grass. And so if you've ever

  • looked at a dandelion leaf, all the veins, which really are vascular material, it's kind

  • of like our circulatory system, moving water and sugar, are going to be net like. They're

  • going to branch out. But if we're talking about a monocot, they're going to be parallel.

  • So if you've ever looked at the veins in the grass, a blade of grass, it's going to be

  • all parallel. If you were to look at their flowers, in a dicot, they're going to have

  • 4 to 5 or multiples of 4 to 5 on their petals. So you can see 1, 2, 3, 4, 5. So probably

  • a dicot. Where as if it's a monocot, they're going to be in multiples of 3. So you can

  • see that this one has 6 petals. And so it's going to be a monocot. And then another way

  • to differentiate between the two is going to be roots. A dandelion, if you've ever tried

  • to pull one out, they have this really big tap root system. But in monocots, like grass,

  • they're going to have a netlike root system. And it's going to be what makes up sod for

  • example and grass. And so those are the different types of angiosperms. When we talk about phytotomy

  • you should realize that plants live a double life. They live life underground. We call

  • that the root system. And then they have a life above ground. We call that the shoot

  • system. Within that shoot system, basically you're going to have nodes. So that would

  • be a node there. A node there. You could have another node there. And another node up here.

  • But the distance between those nodes is going to be the internodes. So that would be the

  • internode between the two. And so basically plants are able to grow up, but they're also

  • able to grow out and each of these node points. Just like use they're going to have tissues.

  • And so in us if we're talking about tissues, now you would think of muscular, excuse me,

  • muscular nervous, connective and then epithelial. But in plants there are just going to be three

  • types of tissues. They have dermal tissue, ground tissue and then vascular tissue. And

  • just like us they break that into specific types of cells. We've got the epidermis, which

  • is the dermal lining. And then we have periderm, which is going to be mostly when we get to

  • the level of bark. So it's secondary growth. Function of that is to provide protection.

  • So this is a cross-section of a leaf. So it's going to provide protection from the outside.

  • Same thing right here. You can see this in a stem. We're going to have dermal tissues

  • on the outside. And they also prevent water loss. So basically epidermis is the big type

  • of dermal tissue. Ground tissue is going to be just run of the mill cells. And so this

  • is going to be broken into three types. And these words are really fun to say. Parenchyma,

  • collenchyma, and sclerenchyma. What do they do? Basically they do the jobs of the plant.

  • So they're going to be the site of photosynthesis for example in the leaf. But it's going to

  • be metabolism, storage, growth. All of that is going to be in the ground tissue. And then

  • finally we have the vascular tissue. That's made up of two type. Xylem and phloem. And

  • they're going to move the water and the sugar. So we'll get more specific to each of these.

  • So let's start with the dermal tissue. Dermal tissue, for the most part is going to be epidermis.

  • So right here we're looking at a cross-section of a leaf. So this would be dermal tissue

  • on the top and on the bottom. The guard cells also make up part of that. And the guard cells,

  • you can see a zoomed in version of it right here. Basically what they do is they surround

  • the stomata, or this opening. What does the stomata do? You can see it's the hole in the

  • leaf. Basically it allows water to evaporate out and that water as it evaporates out is

  • going to carry water all the way up in the plant. But they also bring in a really important

  • gas. That's going to be CO2. And so plants kind of have guard cells that are doing really

  • good feedback. Basically if they have a lot of moisture and they can let a lot of it go

  • and it's really sunny they open the guard cells up. And the stomata are going to allow

  • a lot of water to come out, a bunch of carbon dioxide in. And so they can make a bunch of

  • sugars. Likewise if it's really, really hot, really, really dry, they can close up the

  • stomata. So they don't lose all of their water. One thing that I should mention is going to

  • be this real waxy covering on the epidermis. That's called the cuticle. And it's like wax.

  • It's that wax that you feel, that slippery stuff you feel on the outside of a leaf. And

  • that's going to prevent water from getting in and getting out. If we get to the ground

  • tissue, basic run of the mill cells are going to be parenchyma cells. The typical plant

  • cell is parenchyma cell. What do they do? They're going to be the site of metabolism.

  • Site of photosynthesis. Outside that, as a plant starts to grow we have the collenchyma.

  • I always remember the c and l and collenchyma stands for celery. So those are going to be

  • these real durable cells on the outside of celery. They provide support as it starts

  • to grow. And so you can see the dermis on the outside. Collenchyma cells. And then these

  • are going to be parenchyma cells right here. They provide support. And if you take a plant

  • as it grows, and just mess with it all the time, push it all the time, simulating like

  • wind, the collenchyma gets stronger and stronger and stronger. But it never gets as strong

  • as the sclerenchyma. Sclerenchyma are going to be the really durable, wooded kind of portions

  • of a plant as it start to grow. This is a sclerenchyma fiber that's cut in half. If

  • we were to look at a fiber we could find this. This is hemp. We pulled the sclerenchyma cells

  • out to use these fibers to make rope. It's incredibly durable. And so sclerenchyma is

  • going to be these big fibers that give it that really really strong, like in a branch

  • that grows. But we'll also have sclerenchyma cells like the core of an apple, of example

  • is sclerenchyma. It's protecting the seeds on the inside. Or the grit on the inside or

  • a pear is sclerenchyma. So that's the ground. Now we go to the vascular. Vascular is going

  • to be made up of two types. The xylem and the phloem. So in this we're cutting a stem

  • apart. This would all be xylem in here. And then level 4 right here is going to be phloem.

  • Basically xylem is moving water. It's going to move water from the roots to the shoots.

  • Phloem is going to move sugar up and down in a plant. And so on the outside we'd have

  • dermis. They we're going to have so sclerenchyma cells that are are giving it durable support.

  • So now we're going to talk about growth and then finally finish up with flowers. But this

  • is an old story. If you go and take a spike and hammer it into a tree. Let's say that

  • we put it at about 3 feet right here. And you come back in 100 years. So let's say,

  • make it more realistic, 40 years. And the plant, the tree now, instead of being whatever,

  • 16 feet tall is 160 feet tall. How high is that spike going to be? Well the right answer

  • is that it will still be 3 feet tall. Because plants grow from the top and they grow from

  • the bottom. They from from the shoots and and the roots. But the middle is going to

  • stay the same. Now the bark is going to start to grow up. And so that tree might, the spike

  • might not be as far in, but just like humans we first grow up. Get much, much longer. And

  • they we're going to, I'll tell you this, as you get older you start to get wider and wider

  • and wider. And so we call this primary growth. This first growth. And how does that occur?

  • Well we use something called an apical meristem. Basically that's going to be a site. Right

  • here we're looking at a root where you have cells that keep copying themselves. We call

  • those undifferentiated. Think of it like a stem cell that keeps making copies of itself.

  • And so that's going to make new cells. And as those cells get longer. As they mature

  • and get larger and larger and larger, that's going to push this stem or root in this direction.

  • Now I can tell this right here is going to be a RAM or a root apical meristem because

  • it has this root cap on the top of it. And that root cap is going to allow it to push

  • through the soil to find water. And so the meristem is actually going to produce new

  • cells on this side. Which will make the root cap. And then cells on this side that make

  • this root itself. If we look up at the SAM or the shoot apical meristem, it's not going

  • to have this root cap. Because it's doesn't have to, it's just pushing it's way through

  • air. So it's not going to have this. But it's still going to have this meristem. Because

  • it's producing new cells behind it. And as they mature, it gets bigger and bigger and

  • bigger. So that's going to allow us to grow up and down. But we also have secondary growth.

  • Secondary growth allows us to get wider. And so secondary growth, think about wooded growth.

  • And so we're looking at a tree now in this diagram that has been sliced in half. And

  • we're zooming in kind of to the bark portion. And so basically what you have is xylem. So

  • xylem is going to be here on the inside. So let's put an X for the xylem. And then you're

  • going to have phloem here. And so what's creating the xylem and the phloem. This layer called

  • vascular cambium. So what it's doing is producing new xylem here and it's prodding phloem on

  • this side. The phloem remember moves the sugar and the xylem is going to move the water.

  • So we've got xylem, vascular cambium, phloem. As we move up you have a layer called the

  • feloderm which isn't found in all plants, so let me cross that out. And then we have

  • the cork cambium. The cork cambium is another meristomatic layer. And that, just like the

  • vascular cambium made phloem and xylem, cork cambium is going to make this water proof

  • cork on the outside. And so this guy right here is peeling bark back from a tree. And

  • so what is he exposing right here? He's really exposing the vascular cambium. He's got xylem

  • on the inside, phloem on the outside. And so what he would really do if this is a tree

  • that's just standing, he would be girdling the tree. He'd be killing the tree. Because

  • if you remove that phloem and everything out, then sugar can't move up and down in a plant.

  • You'd still have the xylem here, but without sugar you can't have life. And so one thing

  • you know around here when you cut down a tree is what you will get are theses rings. And

  • so you see these rings. What are those rings? Well the inside of a tree, wood for that matter,

  • is going to be xylem. And so basically what happens is it's going to be wider when the

  • cells are laid down during summer because it's growing really really quickly. But in

  • the fall it's going to be more dense. And in the spring, because we can't grow as quickly

  • and not at all in the winter, and so you get these seasonal rings. And so we can count

  • them when it's growing fast, slow, fast, slow. And we can count the years, if we take a core

  • sample. What would this look like in an area where there is no seasons? It's basically

  • going to be uniform all the way out. Okay. So that's secondary growth. Last thing I want

  • to finish with is the reproductive structure. We call that the flower in angiosperms. Basically

  • there's the male part. That right here is going to be the stamen. And then we're going

  • to have this, the female part. And so the stamen right here is going to have on the

  • head of it, we call this the anther. It's going to produce pollen grains. Those pollen

  • grains are sperm essentially protected. So those pollen grains, if they float away or

  • are carried by a bee away, is going to be the male reproductive structure. Female structure

  • is going to be way down here inside the ovary in this structure called the ovule. And so

  • the egg is going to be protected right down here. And then it's surrounded by an ovary.

  • Which will eventually ripen to form fruit. But the way reproduction works in flowers

  • is different than us. It's just not sperm meets egg. What we have is called double fertilization,

  • which is kind of crazy but really, really cool. So let's say that the pollen lands right

  • here. Basically what will happen is you'll get this pollen tube that will grow all the

  • way out, all the way down here and it's going to grow into the ovule. Now within that pollen

  • tube we're going to have two sperm. And so we're going to zoom all the way down here

  • into the ovule. So basically the pollen tube is growing all the way down. And now we have

  • these two sperm. So 1, 2 sperm. And those are going to be those blue haploid structures