Introduction to cilia, flagella and pseudopodia
- [Instructor] The goal of this video is to appreciate some of the structures that you see even in unicellular organisms. So this right over here is a picture of the amoeba Chaos carolinense. And what you see here is a projection coming off from the main part of the cell, and this is called a pseudopod, which is referring to it being a false foot. The pod is coming from the same root word as podiatry, which is referring to the foot. And what I really want you to appreciate, this is used by amoeba either to move around or it could be even used to attack something that it wants to engulf. And think about what it might take to be able to do this, to be able to grow this type of a pseudo foot, this type of a false foot. You need all sorts of microstructures in here that will extend or contract as necessary. And think about the machinery that you need to do that. And so the key realization is, sometimes we just imagine cells as these bags of fluid with a few things floating around. But they're these incredibly complex structures, and biologists even today don't fully understand how everything works and they're studying how these things actually come to be. Now another structure that you'll often see in unicellular organisms that either help them move around or even help move other things around are cilia. So this right over here is a picture of Oxytricha trifallax, which is a unicellular organism. It's a eukaryote. And you can clearly see these projections from its body here, these hairlike structures. Remember this is a unicellular organism. If we were to, it's actually a fairly, it's a decent sized one. That would be about, something like that would be about 30 micrometers right over there or 30 millionths of a meter or 30 thousandths of a millimeter. So small by our scale, but it's actually pretty big on the scale of it being a cell. And once again, these cilia tend to move in unison to either allow the microorganism to move around or sometimes they're used to move other things around. For examples the cells that line your lungs will have cilia that are used to move things up or down, to move some of the saliva or any particles that are in there. Now Oxytricha trifallax is particularly interesting as a eukaryote because it doesn't just have one nucleus. It can have two nuclei. And within the nucleus, it's DNA can be extremely fragmented. Most organisms have a reasonable number of chromosomes. Human beings have 23 pair. That's actually a fairly large number. Oxytricha trifallax could have thousands of chromosomes. And what's really interesting about Oxytricha trifallax is how it mates. When it is under stress, it will merge with another Oxytricha trifallax, and instead of producing another offspring, they mingle their DNA together. So by mating, they change each other's genetic makeup, which is fascinating. And depending on your perspective, highly romantic. Now another related idea is instead of having many cilia, some unicellular organisms will just have one large thing that looks like a tail that they can whip around to move. So this right over here is a commonly studied green algae. It's called Chlamydomonas, and you can see very clearly here this flagellum, this tail-like structure. And this is extremely thin. We're seeing it under a very powerful microscope right over here, but just to get a sense of scale. A micrometer here would be about that. So the width of this flagellum, flagellum would be the singular. If we were talking about many of these, we would say flagella. This is about 1/4 of a micrometer. Another way of thinking about it, you could put 4,000 of these side by side, and you would have the width of a millimeter. So extremely extremely small, but once again, it really is amazing that these what seem like simple organisms to us are actually quite complex. There's a whole study of how these flagella move around, how the cell can spin it around so it allows it to move. If you were to actually decompose what's going on in this part of the cell, it's actually quite complex. It's biological machinery going on. So once again, these cells are not these just bags of just a few things floating around. They're incredibly complex structures that we are still trying to understand.
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