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
right here. We have the egg, just like us. This is exactly the same. We have egg and
sperm, but we also have these polar nuclei around the outside. So we have these two other
nuclei. Each of those are haploid. And so basically let's look ahead. With fertilization
one of the sperm fertilizes the egg. This is going to make the new plant or the embryo.
And then we've got the other sperm fertilizing these two polar nuclei. And so this one is
actually going to become triploid and this one is going to become diploid. The diploid
fertilized egg becomes the new plant. The triploid fertilized polar nuclei becomes something
called the endosperm. The endosperm is triploid. Let's zoom ahead to the seed. What does that
look like? Well here's going to be that triploid endosperm. That's going to be food for the
plant. And the plant is going to be the embryo right here. That's diploid. And so basically
when you plant a seed it's protected by this seed coat around the outside. This would be
wheat seed. It's protected by that. But when it starts to germinate that embryo is going
to start to grow. It's going to start to become the plant. But this endosperm is going to
provide the food for that growing plant. As it starts to grow, before it eventually starts
to do photosynthesis and then the whole cycle continues again. And so what have we talked
about? Structure of plants. What's going to be in the next podcast? More of the physiology.
How does this all work? How do we move nutrients around in a plant. But for now I hope that's
helpful.