Protist Cells - Video Tutorials & Practice Problems
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Protist Cells 1
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Hi. In this video, we're gonna talk about protists, which are essentially the category of eukaryotes that includes everything that isn't a plant, an animal, or a fungus. So it's kind of like a biological grab bag or potpourri, It's a real mixture, and as you'll see there aren't really a lot of unifying themes that tie protists together. So let's begin our discussion by talking about eukaryotic cells. Right? Protists are eukaryotes. So what are eukaryotes? Well, you might recall that eukaryotes have, nucleus, they have membrane bound organelles, and these are cytoskeleton. Now, the unifying theme of eukaryotes if you will, is the nucleus. And and let's use a little fancy terminology here. The synapomorphine, right? The derived character, that is, shared between the organisms in a clade, the synapamorphy that unifies eukaryotes is the nucleus. Right? Now, eukaryotes also tend to be much larger than prokaryotes, right here we've got some little prokaryotic cells. Here we have our eukaryotic cells or eukaryotic cell, I should say, just one cell. And eukaryote tends to be a lot larger, it's got this nucleus, you can see all these membrane bound organelles, we have mitochondria here, these are Golgi apparatus, right? There's our, centrioles and, you know, here we're really showing a same, same thing, you know, now you can see the rough ER and the smooth ER. And if you want to review these concepts, go back and check out the video on cells. Before we dive into Proteus, I also want to revisit the idea of endosymbiotic theory. And that is because, endosymbiotic theory is actually going to play into Protest in kind of a unique and pretty darn cool way. So if you recall, the basic idea of endosymbiotic theory is that, as, you know, prokaryotic cells, which were the first form of cells, got bigger, they, you know, they faced this problem, the surface to volume surface area to volume ratio issue that cells and organisms in general run into as they get larger. And so, you know, these infoldings, these membrane infoldings, appeared to help counteract, the, or to to help maintain rather a surface area to volume ratio that was ideal for the organism. Eventually this becomes the nucleus and the endomembrane system and, ultimately, now we're gonna get to the endosymbiotic part, ultimately what's gonna happen is these, these cells are going to engulf Proteobacterium and it's worth noting that a lot of these single celled organisms you know that act as hunters will literally just engulf their prey like this but instead of digesting this bacteria what happened is these 2 organisms, essentially became reliant on each other. They they formed this symbiotic relationship ship where they were helping each other. You know, for example, the larger cell that engulfed the proteobacteriums, like offering protection, probably feeding nutrients to the proteobacterium, and in exchange the proteobacterium is going to, generate a bunch of ATP, by, you know, oxidative phosphorylation. So eventually these proteobacterium, through, you know, what is called symbiogenesis, write that down. So through symbiogenesis these proteo bacterium that were engulfed by prokaryotic cells will eventually become a eukaryotic cell, and those proteobacterium are going to become mitochondria. There's a lot of evidence for this. We're not really going to cover it now, other than saying that, like prokaryotes, which have a double membrane, mitochondria have a double membrane, which is unlike other membrane bound organelles. And the reason I'm mentioning that, will become significant later. So in addition to this, there was also another, symbiogenesis event where cyanobacterium were engulfed and eventually became chloroplasts. Right? So these are both instances of symbiogenesis. We have proteobacterium becoming mitochondria and cyanobacteria becoming chloroplasts. Now with that, let's flip the page and talk about how, protists experience some unique forms of endosymbiosis.
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Protist Cells 2
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While the organisms of the plantae lineage, have chloroplasts as a result of, what we'll call primary endosymbiosis, meaning, they engulfed the cyanobacterium, and that turned into the chloroplast. There are lineages of protists that actually have these quadruple membraned chloroplasts. Right? So remember that bacteria have that double membrane structure to them. Right? So chloroplasts, like mitochondria, have that double membrane. But in certain protists that have, chloroplasts present, they have this quadruple membrane chloroplasts. And people take this as evidence of what's called secondary endosymbiosis. So basically, this organism, this eukaryotic cell, would engulf a photosynthetic eukaryotic cell, like we see happening here. It's gonna engulf it, and then this, photosynthetic eukaryotic cell will eventually become this quadruple membraned chloroplast structure, and this will account for the origin of chloroplasts in other eukaryotic lineages outside the planti lineage. So within planti, it is what we see going on right here. Outside of planti, it is going to be this situation here. Right? They engulfed an organism that already had undergone endosymbiosis, and then there was another endosymbiosis, and we call that secondary endosymbiosis. Now, finally, let's actually get to a little bit about protists. What defines them? Well, not a lot, unfortunately. Protists, again, they're a grouping of convenience. Right? They're basically, everything that does not belong to fungi, animalia, and plantae. Right? Fungus, animals, plants. Every eukaryote that is not in one of those three groups is a protist. So that means that protists are a paraphyletic group. Right? They are not monophyletic, unlike fungi, animals, and plants, which are all mono, which are are monophyletic, Protists are paraphyletic group. So, as a group, they do have some shared features, but many protists will display unique characteristics. And in a later video, we will actually go through and look at some of those characteristics. So most protists are unicellular, but some are colonial, meaning they'll live in colonies, and others actually are multicellular. And these are, like brown algae, red algae, and slime molds. Those are some, examples of multicellular protists. Now, it is, worth noting that multicellularity actually arose independently in many eukaryotic lineages. So, there wasn't some original multicellular organism, and that's where all multicellular organisms came from, instead, many multicellular organisms have cropped up in various, lineages. Right? Right? So you might remember, when we talked about evolution, we said that the I evolved independently 16 over 16 different times. So, just like that, multicellularity arose independently, many times in Eukaryotic lineages. Now, most protists undergo asexual reproduction, which will include mitosis, unlike binary fission. Right? Remember, protists are eukaryotes, so they're going to have a nucleus, which means they're going to need to perform, mitosis when they when the cells divide. However, they generally, sorry. Well, protists, you know, undergo asexual reproduction, but some of them, have evolved a, various forms of sexual reproduction. And remember, sexual reproduction is a major event in evolution because it allows for the introduction of tons of genetic variation, which is super important, for evolutionary purposes. Now, it's, worth looking at this little mock up of a phylogenetic tree, and and I really wanna emphasize mock up. This is not like a very nice phylogenetic tree. I'm really just trying to show one little point here, and that is how much outside of, plants, animals, and fungi, how how many different lineages there are outside of plants, animals, and fungi. So, here, archeplastida, this is this is plants. Right? This is plantae, basically. Now that's not to say that, there aren't protists in this group, but that's where, land plants are. We have fungi over here, and it's, I should note that this whole branch is coming off of this one right here. And so fungi right there, and then you can see down here we have animals. So look at all these other lineages that exist outside of plants, animals, and fungi. Right? These are all the protists. Big big group there. Big big group. And as you can see, lots of distantly related cousins, so to speak. That's what I meant by the this is not a monophyletic group, but a paraphyletic group. There's all these phyla parallel to each other, in this taxonomy. And with that, let's flip the page.
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Protist Cells 3
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As I keep saying, there is nothing that really unifies or defines protists as a group outside the fact that they're all eukaryotes. However, there are certain features that are shared by many protists, across various lineages. So let's talk about a couple of those. One of the coolest, I think, is that protists can be multinucleated, and that is when a single eukaryotic cell will have more than one nucleus. And you'll see this actually comes in a variety of different, forms. One of the craziest of which is, you know, types of slime molds, that we'll take a look at, that actually can have thousands of nuclei in a single cell. It is worth noting that, there are, you know, human cells, for example, that are multinucleated, and these include, types of muscle cells. However, you know, this is just, one feature of protists that you can kind of apply generally. It's like a blanket statement. Of course, there are many protists that are not multinucleated because, again, the grouping of protists is just out of is just out of convenience. There isn't really, like, one unifying or, you know, more than one unifying thing that brings them all together. So, many protists have cell walls or shells actually even, that, serve as protective outer layers. Some of these shells are made of like, inorganic materials. It's super cool. Some of them are very beautiful. We'll actually be taking a look at them when we discuss the various lineages of protists. Now, like all eukaryotic cells, protists can use cilia and flagella for movement as well as, you know, other things. Here we see a picture of cilia. Here we have our flagella. Now I do want to mention that prokaryotic flagella and eukaryotic flagella are actually different. There are structural differences between them and, you know, we have discussed that, previously in the video on cells. I'm not gonna get into that here. I'm just pointing this out because I am using the same picture of flagella that I used when I was, talking about prokaryotic flagella. I just really like the way that these two images look next to each other. So that's why I'm reusing it here. Fear not, just know that they are actually structurally different. The fact that I'm using the same image isn't going to, affect your understanding at all. So, the last kind of, common feature that I want to point out is amoeboid movement. Now many protists are considered amoeba. And amoeba are basically organisms that move by, reshaping their cells and forming what are called pseudopodia, which literally means false foot. Pseudo is false, podia is foot. And you can see an example of these pseudopodia on this amoeba here. These little, tentacle like things that it's stretching out, those are the pseudopodia. And these are literally cytoplasmic protrusions, and the cell will use actin and myosin to, kind of stretch various parts of the membrane out into these pseudopodia. Now it is, worth pointing out since we're talking about pseudopodia and amoeba, there is a lineage of protists called amoebazoa, but amoeba exists in other lineages as well, because amoeba are simply organisms that, reshape their cells and use pseudopodia in or reshape their cells in the form of pseudopodia, to move around. Now, many protists are actually predators. Yeah. Unicellular predators. Not something we often think about, but trust me, it gets savage at the cellular level. Right? You know, they're not like, you know, stunning their prey or something and taking them out in a nice way. No. They do phagocytosis. They literally engulf the whole cell and just eat it like that. You know, almost think like a snake swallowing its prey whole. Now, what's pretty cool is when they do phagocytosis, they're actually using pseudopodia, right, to stretch out the membrane of the cell around the, thing they're trying to eat, which isn't necessarily another cell but it can be, you know, here in this image it just says solid particle, could be like a particle of food. It could also be another cell though. For example, like a bacteria cell or another eukaryotic cell. It is worth noting that some protists actually do use photosynthesis. You might recall we just talked about secondary endosymbiosis, right? So, there are chloroplasts in various forms present in different protists, and they will, do photosynthesis, though many protists do not rely solely on photosynthesis. They they will, do some photosynthesis, but then they'll also, you know, obtain nutrients, in other ways. Now, decomposers actually Oh, before I get to that, love this picture right here. These are protists and these dark dots, those are red blood cells. Yeah, so these are protists that are eating red blood cells inside an animal. As I said, it gets savage on the cellular level. They eat your blood. Now, as I was saying, decomposers absorb nutrients directly across their cell membrane, and usually this is accomplished via transport proteins. So, many protists are decomposers and they will, break down and absorb nutrients from decaying organic matter. And again, they'll take those nutrients in via transport proteins. So these are just some themes that you can apply to protists, but again, bear in mind that it's really not a a very well defined group. It's really just a everything that isn't this stuff group. With that, let's flip the page.