Plant cells발음듣기
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Plant cells
101문장
100% 한국어
번역 22명 참여
출처 : 칸아카데미
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Hank: 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.발음듣기
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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.발음듣기
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The only thing plants need to make themselves a delicious feast is sunlight and water; just sunlight and water.발음듣기
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Everything in it, in fact everything that is in this [McDonalds], in fact, everything you have ever eaten in your life is either made from plants or made from something that ate plants.발음듣기
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So let's talk about plants. (cheerful music) Plants probably evolved more than 500 million years ago.발음듣기
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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.발음듣기
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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.발음듣기
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Some people call these scale tree forests coal forest because there were so many of them, they were so dense and they covered the whole earth, that they eventually fossilized into giant seams of coal, which are very important to our lifestyles today.발음듣기
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See what we did there? Because coal is made of carbon, so they named the epoch of geological history over how face-meltingly intense and productive these forests were.발음듣기
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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 would be freaking awesome.발음듣기
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Anyway, angiosperms, or plants that used 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.발음듣기
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They're called eukaryotic cells, which means they have a good kernel, and that kernel is the nucleus.발음듣기
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Not "nuculus". The nucleus can be found in all sorts of cells: animal cells, plant cells, algae cells. Basically, all the popular kids.발음듣기
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The prokaryotes include your bacteria and your archea, which you've probably met before in your lifetime.발음듣기
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Or if you've ever been in a hot spring, or an oil well or something, they're everywhere: they cover the planet; they cover you.발음듣기
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Like I said, eukaryotes have that separately enclosed nucleus, that is, that all-important nucleus that contains its DNA and is enclosed by a separate membrane, because a eukaryotic cell is a busy place.발음듣기
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Eukaryotic cells also have these little stuff-doing factories called organelles, because we decided that we'd name everything something weird.발음듣기
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But organelles, and they're suspended in cytoplasm, continuing with the really esoteric terminology that you're going to have to know.발음듣기
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Well, basically, if you want to know about the structure of the eukaryotic cell, you should watch my video on animal cells, which let's just link to it right here.발음듣기
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But obviously plants and animals are very different things, so what are the differences in a plant cell that makes it so different from an animal?발음듣기
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First, plants are thought to have evolved from green algae, which evolved from some more primitive prokaryotes.발음듣기
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Something plants inherited from their ancestors was a rigid cell wall surrounding the plasma membrane of each cell.발음듣기
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This cell wall of plants is mainly made out of cellulose and lignin, which are two really tough compounds.발음듣기
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Cellulose is by far the most common and easy to find complex carbohydrate in nature, though if you were to include simple carbohydrates as well, glucose would win that one.발음듣기
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This is because, fascinating fact, cellulose is in fact just a chain of glucose molecules. You're welcome.발음듣기
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If you want to jog your memory about carbohydrates and other organic molecules, you can watch this episode right here.발음듣기
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Animals. But you know what's a real pain in the ass to digest? Cellulose. Plants weren't born yesterday.발음듣기
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Cellulose is a far more complex structure than you'll generally find in a prokaryotic cell, and it's also one of the main things that differentiates a plant cell from an animal cell.발음듣기
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However, the cell wall gives structure to a plant's leaves, roots and stems, and also protects it, to a degree.발음듣기
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The combination of lignin and cellulose is what makes trees, for example, able to grow really, really freaking tall.발음듣기
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It's still useful for us on certain aspects of our digestive system, but it's not nutritious.발음듣기
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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.발음듣기
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A lot of other animals that don't have access to delicious donut burgers have either developed gigantic stomachs, like sloths, or multipe stomachs, like goats, in order to make a living eating cellulose.발음듣기
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These animals have a kind of bacteria in their stomachs that actually does the digestion of the cellulose for it.발음듣기
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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.발음듣기
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But there is another reason why cellulose and lignin are very, very useful to us as humans. It burns, my friends.발음듣기
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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.발음듣기
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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.발음듣기
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Anyway, while we animals are walking around, spending our lives searching for ever more digestable plant materials, plants don't have to do any of that.발음듣기
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Another thing that plant cells have that animal cells just don't have are plastids, the organelles that plants use to make and store compounds that they need.발음듣기
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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.발음듣기
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Like maybe some [produ-select] cell absorbed a bacteria and it found that instead of just digesting that bacteria for the energy that it had, it could use that bacteria.발음듣기
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That bacteria could create energy for the cell or convert light into lovely glucose compounds, which is crazy.발음듣기
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Nobody's really precisely sure how this happened, but they know that it did happen because plastids and mitochondria have double membranes: one from the original bacteria, and one from the cell as it wrapped around it.발음듣기
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Cool, huh? Anyway, the most important of the plastids are the chloroplasts, which convert light energy from the sun into sugar and into oxygen, which the plant doesn't need, so it just gets rid of it.발음듣기
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All of the green parts of a plant that you see: the leaves, the non-woody stems, the unripened oranges, are all filled with cells that are filled with chloroplasts, which are making food and oxygen for you. You're very welcome, I'm sure.발음듣기
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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.발음듣기
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Usually, when the soil dries out or the 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.발음듣기
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It can contain water, which plants need to save up, just in case, and also other compounds that the cell might need.발음듣기
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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. Now, let's do this.발음듣기
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One, they have a cell wall that's made out of cellulose, and so it's really rigid and not messing around.발음듣기
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Two, they've got a nucleus in its own little baggie that's separate from all the other organelles.발음듣기
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It stores the genetic information for a plant and also access the cell's activities director, telling it how to grow, when to split, when to jump and how high, that sort of thing.발음듣기
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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.발음듣기
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Three, they've got plastids, including chloroplasts, which are awesome, green, food-making machines.발음듣기
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Four, they have a central vacuole that stores water and other stuff, and helps give the cell structural support.발음듣기
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And so, stack these cells on top of one another, like apartments in an apartment building, and you had a plant.발음듣기
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All of these unique features are what makes it possible for plants to put food on our table and air in our lungs.발음듣기
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