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- [Voiceover] Let's give ourselves an overview, or synthesis, of all that we've learned about plant and animal cells, and what I have over here on the left, this is supposed to be indicative of an animal cell. Animal cell. And what I have on the right, this should be indicative of a plant cell. Plant cell. So let's start with the, what's outside of the cell. So we see in both of them, we see the extracellular matrix. You see on this animal or outside of this animal cell, you see all these collagen fibers and everything else, all these fibers that are holding these cells into place and allow these cells to relate to each other, and actually, depending on what's inside of it, can even help signal different things to the cells, so this is an extracellular matrix. Now when we think about the extracellular matrix for a plant cell, we also think about, there's some other components that are involved in the actual cell wall, and so the cell wall is a key difference between plant and animal cells. So, the cell wall is going to be in a plant cell. Animal cells don't have cell walls. Now, if we go one layer deeper, we get to the plasma membrane, the cellular membrane, and we see that that is common to both. The animal cell is going to have a plasma membrane and the plant cell is going to have a plasma membrane and they actually can both have tunnels from neighboring cells, or tunnels between neighboring cells. We studied that in the cell wall video for plant cells. We saw these things right over here, called plasmodesmata, And we can actually see a complete one over here, because I start to draw a little bit of an adjacent cell. Plasmodesmata. And in animal cells, the analog are gap junctions, which are still tunnels between adjacent cells. So, gap junctions. Now, plasmodesmata are much more common to a much wider category of plant cells than gap junctions but gap junctions can be very relevant in certain types of animal cells, in particular, things like heart cells, where because of gap junctions between adjacent cells, electrical signals can move through the tissue and let adjacent cells know, hey, it's time to contract in the right way, so this is still very crucial for certain types of animal cells. So now let's go a layer even deeper, and actually, before I do that, I want to reemphasize this, and I do this in almost every video. All of these membranes that we draw, either the outercellular membrane or the membranes of these organelles, these are all lipid bilayers, or phospholipid bilayers, so if I were to zoom in, right over there, on this yellow place right over there, it looks just like a line, but it really is, it really is a, they really are these phospholipid, these phospholipid bilayers that have these hydrophilic heads that point outwards and these hydrophobic tails that point inwards, and it keeps going, I want to make that very clear. These lipid bilayers, all of these membranes that I draw, are lipid bilayers. But let's keep on going. So as we go now into the cell, we see that both of these cells have cytoskeletons. We have cytoskeletons, so, you have your microfilaments right over here, microfilaments right over here, and I'm not giving full justice to the complexity, just 'cause we want to be able to have a fairly simple-looking diagram. You have your microtubules, microtubules. You might have intermediate filaments, and we talk about all of those things in other videos, but now, let's dig a little bit deeper, so in the animal cells, I have these centrosomes, and they are key for organizing the microtubules, and we're gonna see them a lot when we talk about mitosis. We don't see them in plant cells. They actually figure out other ways to organize their microtubules, especially, well, in general, and especially when we're thinking about something like mitosis, but let's see what other differences are here. Well one big thing that you might notice is this big blue, balloon, egg-looking thing, and this doesn't contain these green things, it's really just behind these green things, and this is, these tend to be associated with plant and fungal cells. This is a central vacuole. Central vacuole. And a central vacuole can store fluid, it can store enzymes, it can be viewed as a place for waste, and actually, it turns out that even though they're common to plants, that depending on which plants, which cells, they can have very different roles, and I want to emphasize this to you, and I do this in other videos. We keep seeing all these organelles, and we can draw pictures, we can draw diagrams of them, and we think we know what most of their functions are, but almost all of these organelles and all of actually, the cell, is an area of active research. In the decades to come, we're gonna find more and more things that these different organelles do, and ways that they signal to each other and interact with each other and behave in different circumstances, so we're starting to understand what's there and have an idea of what they do, but in the decades to come, we're gonna learn much, much, much more about the different structures and functions of a cell, but as I mention, this is a central vacuole. It's large, it can help provide structural support for the cell, it can help store things, and the best analogue on the animal cells, some animal cells actually can have a vacuole, not all of them, but the best analogue is the lysosome, so this right over, just in the orange color, this right over here is a lysosome. Lysosome, lysosome, and a lysosome could be viewed as the waste-disoposal of an animal cell, where it's going to have a bunch of enzymes in it, so that things can kind of go in there and get broken up. It has a low, a relatively low pH, a more acidic pH so that things can be broken up in different ways and then their individual pieces can be recycled, and since we're in this category of places where things go to get, maybe, broken down or catabolized or metabolized in certain ways, it's also worth talking about the peroxisomes. Peroxisomes. So the peroxisomes we actually see in both of them, and they're named that way because when they were first studied, they said, "hey there's something going on here "where there's some oxidation reactions going on here." "Well it seems like the final byproduct seems to be hydrogen "peroxide," and so that's why they were named peroxisomes and we're still understanding exactly all of the things that they do, but we know that they're important for cutting up long-chain fatty acids, so they can be more usable by other parts of the cells, but they also have other roles and all of their mechanisms are still not fully understood. Now going back to differences between the plant cell and the animal cells, a key difference is going to be these characters right over here. These are chloroplasts. These are where photosynthesis takes place, and clearly we're gonna show it in the plant cell. This is how they take, they're able to create, they're able to create, essentially, food or, I guess you could say, fixed carbon, based on light energy, so let me see, chloroplast. Chloroplast, right over there. We do not see that in the animal cell. Now, when we're talking about energy, we talk about the ATP factories of cells, and we find this in both of these cells, and that, of course, are the mitochondria, and we see the mitochondria in both of the cells, and then the other things we also see a lot of common things. We see golgi, we see the golgi apparatus in that cell, we see golgi apparatus in that cell, and that's where we package proteins for use either within the cell or outside of the cell. We have the endoplasmic reticulum. We have the rough endoplasmic reticulum that has ribosomes bound to the membrane, and we have the smooth, where you don't have the ribosomes, an this is where a lot of proteins get manufactured, but including and all, but even lipids also can get manufactured. Then you have, of course, the nuclear membrane. Actually, this is the inner nuclear membrane right over here. The outer membrane is contiguous with the endoplasmic reticulum, but you see that in both of these cells, and inside, of course, you have the DNA. It's in chromatin form, and then you have this, kind of, extra-dense area that shows up in microscopes which we call the nucleolus, which is associated, which is as associated with ribosomal, with ribosome formations and ribosomal RNA, and of course, you also have free ribosomes. Free, you also have free ribosomes. So this is a very high level overview of cells, eukaryotic cells, I should say, but hopefully it also starts to show you some of the key distinctions between animal and plant cells.