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  • 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.