Plant Cells: Crash Course Biology #6

Plant Cells: Crash Course Biology #6

August 15, 2019 100 By Ewald Bahringer


Plants are freaking great because
they have this magical wizard power that allows them to take carbon dioxide out of the air
and convert it into wonderful, fresh, pure, oxygen for us to breathe. They’re also way cooler than us because,
unlike us and every other animal on the planet, they don’t require all kinds of Hot Pockets
and fancy coffee drinks to keep them going The only thing plants need to make themselves
a delicious feast is sunlight and water. Just sunlight and water! Paula Deen can’t do that and she makes fried-egg
bacon donut burgers. I’m telling you this is surprisingly good. This is a different kind of magic. But you know, part of this is plants! And
everything in it, in fact, everything that is in this McDonalds in fact, everything that you have ever eaten
in your life is either made from plants, or from something that ate plants. So, let’s talk about plants! Plants probably evolved more than 500 million
years ago. The earliest land-plant fossils date back more than 400 million years ago.
These plants were lycophytes which are still around today and which reproduce through making
a bunch of spores, shedding them, saying a couple of Hail Marys and hoping for the best. Some of these lycophytes went on to evolve
into “scale trees,” which are now extinct, but huge, swampy forests of them used to
cover the Earth. Some people call these scale tree forests
“coal forests” because there were so many of them and they were so dense and
they covered the whole Earth and they eventually fossilized into giant
seams of coal, which are very important to our lifestyles today. So this is now called the Carboniferous Period. See what they did there? Because Coal is made
out of carbon, so they named the epoch of geological history over how face-meltingly
intense and productive these forests were. I would give my left eyeball, three
fingers on my left hand — the middle ones, so that I could hang loose — and my pinky
toe if I were able to go back and see these scale forests because they were freaking awesome. Anyway, Angiosperms, or plants that use flowers
to reproduce, didn’t develop until the end of the Cretaceous Period, about 65
million years ago, just as the dinosaurs were dying out. Which makes you wonder if in fact the first
angiosperms assassinated all the dinosaurs. I’m not saying that’s definitely what
happened, I’m just saying it’s a little bit suspicious. Anyway, on the cellular level, plant and animal
cells are actually pretty similar. They’re called eukaryotic cells, which means they
have a “good kernel.” And that “kernel” is the nucleus. Not “new-cue-lus.” And the nucleus can be found in all sorts of cells. Animal cells, plant cells, algae cells. You know, basically all of the popular kids. Eukaryotic cells are way more advanced than
prokaryotic cells. We have the eukaryotic cell and we have the prokaryotic cell. Prokaryotic basically means “before the kernel.”
Pro-kernel. And then we have eukaryotic, which means “good
kernel!” The prokaryotes include your bacteria and
your archaea, which you’ve probably met before in your lifetime, every time you’ve
had strep throat, for example, or if you’ve ever been in a hot spring or an oil well or
something. They’re everywhere. They covered the planet. They cover you! But like I said, eukaryotes have that separately
enclosed nucleus. That all important nucleus that contains its DNA and is enclosed by a
separate membrane Because the eukaryotic cell is a busy place
— there’s chemical reactions going on in all different parts of the cell — it’s important
to keep those places divided up. Eukaryotic cells also have these little stuff-doing
factories called organelles. I guess we decided we would name everything something weird… But, organelles. And they’re
suspended in cytoplasm, continuing with the really esoteric terminology that you’re going
to have to know. Cytoplasm is mostly just water, but it’s some
other stuff too. Well basically if you want to know about the structure of the eukaryotic
cell you should watch my video on animal cells. Let’s just link to it right here. Plant and animal cells are very similar environments.
They control themselves in very similar ways, but obviously, plants and animals are very
different things. What are the differences in a plant cell that
makes it so different from an animal? Well that’s what we’re going to go over now. First, plants are thought to have evolved
from green algae, which evolved from some more primitive prokaryotes, and something
plants inherited from their ancestors was a rigid wall surrounding the plasma membrane
of each cell. So, this cell wall of plants is mainly made
of cellulose and lignin, which are two really tough compounds. Cellulose is by far the most common and easy
to find complex carbohydrate in nature, although if you were
to include simple carbohydrates as well, glucose would win that one. And this is because, fascinating fact:
cellulose is just a chain of glucose molecules! You’re welcome. If you want to jog your memory about carbohydrates
and other organic molecules, you can watch this episode
right here. Anyway, as it happens, you know who needs
carbohydrates to live? Animals. But you know what’s a real pain in the ass to digest?
Cellulose. Plants weren’t born yesterday. Cellulose is a far more complex structure
than you will generally find in a prokaryotic cell, but it’s also one of the main things
that differentiates a plant cell from an animal cell. Animals cells don’t have this rigid cell
wall–they have just a flexible membrane that frees them up to move around and eat
plants and stuff. However, the cell wall gives structure to a plant’s leaves, roots and
stems, and it also protects it to a degree. Which is why trees aren’t squishy and don’t
giggle when you poke them. The combination of lignin and cellulose is
what makes trees, for example, able to grow really, really freaking tall. Both of these compounds are extremely strong
and resistant to deterioration. When we eat food, lignin and cellulose is
what we call “roughage” because we can’t digest it. It’s still useful for us in certain
aspects of our digestive system, but it’s not nutritious. Which is why eating a stick is really unappetizing. And like, your shirt. This is a 100% plant
shirt, but it doesn’t taste good. We can’t go around eating wood like a beaver
or grass like a cow because our digestive systems just aren’t set up for that. However, other animals that don’t have access
to delicious donut burgers have either developed gigantic stomachs like
sloths or multiple stomachs like goats in order to make a living eating
cellulose. These animals have a kind of bacteria in their
stomach that actually does the digestion of the cellulose for it. It breaks the cellulose
into individual glucose molecules, which can then be used for food. But other animals, like humans — mostly carnivores — don’t have any of that kind of bacteria, which is why it’s so difficult for us to digest
sticks. Ah! But there is another reason why cellulose
and lignin are very very useful to us as humans: It burns, my friends! This is basically what would happen in our
stomachs. It’s oxidizing. It’s producing the energy that we would get out of it if we were
able to, except it’s doing it very very quickly. And this is the kind of energy, like, this
energy that’s coming out of it right now, is the energy that would be useful to us if
we were cows. But we’re not. So instead, we just use it
to keep ourselves warm on the cold winter nights. Ow! It’s on me! Ow! Ahh! Anyway, while we animals are walking around,
spending our lives searching for ever more digestible plant materials, plants don’t have
to do any of that. They just sit there and they make their own food. And you know how
they do that? They do it with photosynthesis! Another thing that plant cells have that animal
cells just don’t have are plastids, organelles that plants use to make and store compounds
that they need. And you wanna know something super interesting
about plastids? They and their fellow organelles, the mitochondria
that generate energy for the cell, actually started as bacteria
that were absorbed into plant cells very early in their evolution like maybe some protist-like cell absorbed
a bacteria, and it found that instead of digesting that bacteria for the energy that it has,
it could use that bacteria. That bacteria could create energy for the cell or convert
light into lovely glucose compounds, which is crazy! Nobody’s really, precisely sure how this happened,
but they know that it did happen because plastids and mitochondria both have double membranes.
One from the original bacteria, and one from the cell as it wrapped around it. Cool, huh? Anyway, the most important of the plastids
are chloroplasts, which convert light energy from the sun into the sugar and
into oxygen, which the plant doesn’t need, so it just gets rid of it. All the green parts of a plant that you see
— the leaves, the non-woody stems, the unripened oranges — are all filled
with cells which are filled with chloroplasts, which are making food and oxygen
for you. You’re very welcome, I’m sure. Another big difference between a plant cell
and an animal cell, is the large, central vacuole. Plant cells can push water
into vacuoles which provides turgor pressure from inside the cell, which
reinforces the already stiff cellulose wall and makes the plant rigid
like a crunchy piece of celery or something. Usually when soil dries out or a celery stalk
sits in your refrigerator for too long, the cells lose some water,
turgor pressure drops, and the plant wilts or gets all floppy. So, the vacuoles are also kind of a storage
container for the cell. It can contain water, which plants need to save up, just in case.
And also other compounds that the cell might need. It can
also contain and export stuff the cell doesn’t need anymore, like wastes. Some
animal cells also have vacuoles, but they aren’t as large and they don’t have
this very important job of giving the animal shape. So now, let’s do this. Let’s just go over
the basics of plant cell anatomy: 1. They’ve got a cell wall that’s made
out of cellulose and so it’s really rigid and not messing around. 2. They’ve got a nucleus in its own little
baggie that’s separate from all the other organelles. This is basically the headquarters
of any eukaryotic cell: it stores all the genetic information for the
plant and also acts as the cell’s activities director, telling it how to grow, when to
split, when to jump and how high…that sort of thing. Animal
cells have this kind of nucleus too, but prokaryotes don’t. Which is why they’re stuck hanging
around in oil wells and stuff. 3. They’ve got plastids, including chloroplasts,
which are awesome green food-making machines. 4. They’ve got a central vacuole that stores
water and other stuff and helps give the cell structural support. And so, stack these cells on top of one another
like apartments in an apartment building and you’ve got a plant! And all of these unique features are what
make it possible for plants to put food on our table and air in our lungs. So next time
you see a plant, just go ahead and shake its hand and thank
it for its hard work and its service. Now, we went over that stuff pretty fast,
so if you want to go back and listen to any of it, we have a review section over here
for stuff that you may not have totally picked up on or just want to watch again. It’s not a huge piece of your life to re-watch
some stuff so go ahead and click on these things. If you have questions to do with plant cell
anatomy, please leave them for us in the comments and we will hopefully get to those. You can also hook up with us on Facebook and
Twitter of course and we will see you on episode 7 of Biology Crash Course.