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 human cells, for example, that are multinucleated, and these include types of muscle cells. However, 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 convenience. There isn't really like one unifying, or more than one unifying thing that brings them all together.
So, many protists have cell walls or shells that serve as protective outer layers. Some of these shells are made of 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 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 we have discussed that, previously in the video on cells. I'm not going to 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 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 Amoebozoa, but amoeba exists in other lineages as well, because amoeba are simply organisms that 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 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 will do some photosynthesis, but then they'll also 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 not a very well-defined group. It's really just an 'everything that isn't this stuff' group
With that, let's flip the page.