plants are freaking great becausethey have this magical wizard power that allows them to take carbon dioxide out of the airand 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 pocketsand fancy coffee drinks to keep them going the only thing plants need to make themselvesa delicious feast is sunlight and water. just sunlight and water! paula deen can't do that and she makes fried-eggbacon 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! andeverything in it, in fact, everything that is in this mcdonalds in fact, everything that you have ever eatenin 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 millionyears 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 makinga bunch of spores, shedding them, saying a couple of hail marys and hoping for the best.
some of these lycophytes went on to evolveinto "scale trees," which are now extinct, but huge, swampy forests of them used tocover the earth. some people call these scale tree forests"coal forests" because there were so many of them and they were so dense andthey covered the whole earth and they eventually fossilized into giantseams 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 madeout of carbon, so they named the epoch of geological history over how face-meltinglyintense and productive these
forests were. i would give my left eyeball, threefingers on my left hand -- the middle ones, so that i could hang loose -- and my pinkytoe if i were able to go back and see these scale forests because they were freaking awesome. anyway, angiosperms, or plants that use flowersto reproduce, didn't develop until the end of the cretaceous period, about 65million years ago, just as the dinosaurs were dying out. which makes you wonder if in fact the firstangiosperms assassinated all the dinosaurs. i'm not saying that's definitely whathappened, i'm just saying it's a little bit
suspicious. anyway, on the cellular level, plant and animalcells are actually pretty similar. they're called eukaryotic cells, which means theyhave 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 thanprokaryotic 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 "goodkernel!" the prokaryotes include your bacteria andyour archaea, which you've probably met before in your lifetime, every time you'vehad strep throat, for example, or if you've ever been in a hot spring or an oil well orsomething. they're everywhere. they covered the planet. they cover you! but like i said, eukaryotes have that separatelyenclosed nucleus. that all important nucleus that contains its dna and is enclosed by aseparate membrane because the eukaryotic cell is a busy place-- there's chemical reactions going on in
all different parts of the cell -- it's importantto keep those places divided up. eukaryotic cells also have these little stuff-doingfactories called organelles. i guess we decided we would name everything something weird... but, organelles. and they'resuspended in cytoplasm, continuing with the really esoteric terminology that you're goingto have to know. cytoplasm is mostly just water, but it's someother stuff too. well basically if you want to know about the structure of the eukaryoticcell 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 verydifferent things. what are the differences in a plant cell thatmakes it so different from an animal? well that's what we're going to go over now. first, plants are thought to have evolvedfrom green algae, which evolved from some more primitive prokaryotes, and somethingplants inherited from their ancestors was a rigid wall surrounding the plasma membraneof each cell. so, this cell wall of plants is mainly madeof cellulose and lignin, which are two really tough compounds. cellulose is by far the most common and easyto find complex
carbohydrate in nature, although if you wereto 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 carbohydratesand other organic molecules, you can watch this episoderight here. anyway, as it happens, you know who needscarbohydrates 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 structurethan you will generally find in a prokaryotic cell,
but it's also one of the main thingsthat differentiates a plant cell from an animal cell. animals cells don't have this rigid cellwall--they have just a flexible membrane that frees them up to move around and eatplants and stuff. however, the cell wall gives structure to a plant's leaves, roots andstems, and it also protects it to a degree. which is why trees aren't squishy and don'tgiggle when you poke them. the combination of lignin and cellulose iswhat makes trees, for example, able to grow really, really freaking tall. both of these compounds are extremely strongand resistant to deterioration. when we eat food, lignin and cellulose iswhat we call "roughage" because we can't
digest it. it's still useful for us in certainaspects 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% plantshirt, but it doesn't taste good. we can't go around eating wood like a beaveror grass like a cow because our digestive systems just aren't set up for that. however, other animals that don't have accessto delicious donut burgers have either developed gigantic stomachs likesloths or multiple stomachs like goats in order to make a living eatingcellulose.
these animals have a kind of bacteria in theirstomach that actually does the digestion of the cellulose for it. it breaks the celluloseinto 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 digeststicks. ah! but there is another reason why celluloseand lignin are very very useful to us as humans: it burns, my friends! this is basically what would happen in ourstomachs. it's oxidizing. it's producing the energy that we would get out of it if we wereable to, except it's doing it very very quickly.
and this is the kind of energy, like, thisenergy that's coming out of it right now, is the energy that would be useful to us ifwe were cows. but we're not. so instead, we just use itto 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 haveto do any of that. they just sit there and they make their own food. and you know howthey do that? they do it with photosynthesis! another thing that plant cells have that animalcells just don't have are plastids, organelles
that plants use to make and store compoundsthat they need. and you wanna know something super interestingabout plastids? they and their fellow organelles, the mitochondriathat generate energy for the cell, actually started as bacteriathat were absorbed into plant cells very early in their evolution like maybe some protist-like cell absorbeda 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 convertlight 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 plastidsare chloroplasts, which convert light energy from the sun into the sugar andinto 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 filledwith cells which are filled with chloroplasts, which are making food and oxygenfor you.
you're very welcome, i'm sure. another big difference between a plant celland an animal cell, is the large, central vacuole. plant cells can push waterinto vacuoles which provides turgor pressure from inside the cell, whichreinforces the already stiff cellulose wall and makes the plant rigidlike a crunchy piece of celery or something. usually when soil dries out or a celery stalksits 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 storagecontainer 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 canalso contain and export stuff the cell doesn't need anymore, like wastes. someanimal cells also have vacuoles, but they aren't as large and they don't havethis very important job of giving the animal shape. so now, let's do this. let's just go overthe basics of plant cell anatomy: 1. they've got a cell wall that's madeout of cellulose and so it's really rigid and not messing around. 2. they've got a nucleus in its own littlebaggie that's separate from all the other organelles. this is basically the headquartersof any eukaryotic cell: it
stores all the genetic information for theplant and also acts as the cell's activities director, telling it how to grow, when tosplit, when to jump and how high...that sort of thing. animalcells have this kind of nucleus too, but prokaryotes don't. which is why they're stuck hangingaround 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 storeswater and other stuff and helps give the cell structural support. and so, stack these cells on top of one anotherlike apartments in an apartment building
and you've got a plant! and all of these unique features are whatmake it possible for plants to put food on our table and air in our lungs. so next timeyou see a plant, just go ahead and shake its hand and thankit 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 herefor 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-watchsome stuff so go ahead and click on these things. if you have questions to do with plant cellanatomy, please leave them for us in the comments
and we will hopefully get to those. you can also hook up with us on facebook andtwitter of course and we will see you on episode 7 of biology crash course.
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