 That was vanilla ice, really? You know, you know it's getting to be a long day when I start seeing vanilla ice, ice baby. Oh man, it's all bad. Go ahead and draw this little picture. What in the world really, where are we now? Where are we now? Where am I now? Don't worry, I'm still with you. Now let's talk about osmosis. Osmosis has nothing to do with vanilla ice, ice baby. And it's, all right, take a deep breath. Osmosis is the movement of water. But it's the movement of water, movement of water. It's not just the movement of water. It's the movement of water across a semi-permeable mimimar. Semi-permeable, semi-permeable, what, go ahead and guess. I collaborate and listen. Membrane, oh man, osmosis is the movement of water across a semi-permeable membrane, really? Here's, look, here's the deal. We can have particles. I'm going to draw some particles in here. I'm going to draw a whole bunch of particles on this side. And I want you to imagine for a second, okay, think, think osmolarity. These are my particles. Give me a number. Which side of this little YouTube is more concentrated? There's more particles on this side. So this side has a higher osmolarity. Do you agree with that? Totally. So the next question is, well, what's going to happen? Where's water going to move? Well, we don't really know. If you had to guess about the movement of the particles, where's the, where are the particles going to go? Hopefully, you now know that the particles, right, are going to move across the membrane. And they're going to move across the membrane to what? Until the concentration on both sides of this U membrane are the same. Do you agree with that? We're going to, the diffusion of the particle is going to happen until the concentrations are the same on both sides. And when the concentrations are the same on both sides, after they're the same on both sides, then particles, water, everything, they're still going to be moving. They're going to just move to one side at the same rate that they're going to move to the other side. They're just going to diffuse around because of random molecular motion. But the rates that they move in different directions are going to be the same. They're in equilibrium. Before this all happened, before it all happened, is that equilibrium? No, it's not in equilibrium. We're going to have diffusion that takes place. The particles are going to diffuse. We'll write that down. Particles diffuse. And they diffuse if they can. And we can see that in this case, the particles are going to diffuse. You can imagine, like, would water go anywhere? Not really. Like, the water's not going to do anything in this particular case because the particles can diffuse across that membrane. That works for you, doesn't it? I wonder if I can erase this thing. That's magical. Really? That made me really happy right there. You know it's a good day when that makes me happy. So we're back to our original scenario. And this time, I'm going to change the characteristics of this membrane right here. I'm going to now say that this membrane is semi-permeable. I'm going to say that now, guess what? This membrane is semi-permeable. And that means some things can go through and some things cannot. And the characteristics of the membrane will determine what can go through and what cannot go through. But I'm going to say that this membrane is semi-permeable. And guess what? Those little particles are like, dude, get me the heck out of here. Everybody's over here. It's like me cramming y'all in the corner. I'll cram you all in the corner. And what are you going to want to do? Get me out of the corner. Makes complete sense. Of course, you're going to want to get out of the corner. And of course, these guys are going to want to get over to this like open free zone. The molecules are going to want to diffuse, but they can't get through the semi-permeable membrane. The concentrations want to be the same. And so really, they want to be the same. I shouldn't ever say things like that because it's not like they're not little people. But look what happens if the molecules cannot move through the semi-permeable membrane. Water will. Water will move. Now you tell me what direction is water going to move? What direction is water going to move if it wants to have equal concentrations on both sides? Hopefully, you're like, I see, I visualized this. Water can move into the, like basically, for lack of a more scientific way of thinking of it, there's all sorts of math that explains this, which I am a fan of people who understand that. I'm cool with the visualization that there's a whole bunch of stuff over here and the water wants to come over and dilute it. There's all molecular and there's mathematical explanations for how and why this happens. But if water starts to move across the semi-permeable membrane to dilute this side, what's going to happen to the volume of solution on this side? Do you agree water's coming across and the volume is actually going to go up and the volume on this side is going to go down? I agree with that because the water's going to move. The water's moving from one side to the other side. It's moving into the really concentrated side because water can pass across that membrane. The particles cannot. That right there, that's the process of osmosis. The process of osmosis, can you visualize that? That could actually do work. There's actually pressure here. In fact, you could put a little, like what is pressure? It's force per unit area. You could put a little stopper in this and you could push down on the stopper and you could push that water back to the original equal heights and the amount of pressure that you would have to apply to get that to go back to the heights that it originally was. That amount of pressure is the osmotic pressure in this little system, osmotic pressure. If the osmotic pressure between two systems is different, then one of them is going to explode. Now imagine, if water is going to rush into a cell because of osmosis, water can go through our cell membranes. It just will diffuse right in. If water goes in because the cell has a concentration that's higher than the fluid around it, what's going to happen to our cell, dogs? It's going to pop. The cell is going to pop. It's going to explode. This is what we're doing in lab. We have two osmosis labs. I think the first one is we're going to explode some red blood cells for real. We're going to throw some molecules into our, some red blood cells into various solutions and we're going to look at the red blood cells in our microscope and watch them explode. Watch them get big. Watch them shrink. It's really cool because we can see the size changing as the water goes in and out of those red blood cells. I don't know what I did with your lab handout. This is an old lab handout. You need to read your lab handout before coming to class and read through the lab number one, whatever day I see, Monday. Read through the lab number one, whatever it is. I think it's the red blood cells. Read through that one and we'll talk about it in lecture if you have questions. If you're kind of like, I can't imagine what's actually going to happen here, then we'll talk about it in lecture. Also on your lab handout is this little cell activity. Cells are sitting inside beakers of fluid and you have to figure out like what's going to happen to the cell itself. Like is the cell going to swell? Is it going to shrink? Is it going to explode? Is nothing going to happen to it? Because that's actually what we care about. We care about how our cells are reacting to their surrounding. And if your cells are all exploding and popping, do you think that's a good thing? It's not a good thing. I feel like there's something else I need to tell you about osmosis. There's something else I want to tell you about osmosis. Ready? Let's draw this last thing. This is a beaker. This is what your little activity on your lab looks like. This is a beaker and inside this beaker is a cell. And does anybody remember what the concentration of a cell is? Go ahead. Maybe if you yell it really loud, I'll be able to hear it. Just kidding. We're just going to round it up to .3 osmols. And why osmols? Why not molarity? Because we care about osmolarity when we're talking about physiology. You're going to have to go between molar, molarity, and osmolarity, but we think about osmolarity. Now look and be amazed if the solution that this cell is sitting in is .3 osmolarity. Then what's going to happen? What's water going to do in this particular scenario? You know what? Water is going to go in and out. Do you agree with it? Water doesn't have any reason to go in and try and dilute this. There's a whole bunch of particles in here. But there's the same number of particles out here, right? So guess what? This is cool. The concentrations, the osmolarity, are the same inside and outside. But I'm about to make it a little trickier for you. If I make this particle a penetrating particle, that is going to change this scenario. It's penetrating. What does that mean, do you think? If the green particles are penetrating, what does that mean? That means that the particle can pass through the cell membrane most of the time. And we're just going to, we'll make this assumption that our .3 osmolarity, all the particles that are inside your cell that are creating that concentration, they're not penetrating particles. What does that mean? Those guys are not penetrating. What that means is that they can't go through the cell membrane. They can't go back and forth. So they're stuck inside, but the green ones can go in, right? What's going to happen to the concentration? What's going to happen to the osmolarity of that cell when those green particles go in? They're going to go down their own concentration gradient. The last analogy is that particles are like teenagers. They only care about themselves. Hopefully you are not teenagers because then I didn't just offend half my students. So these particles, they don't care. The green ones only care about the concentration of other green ones. The concentration of other green ones inside the cell is like, meh, zero. The concentration of other blue ones outside is zero, but the green ones, they can't get out because they're not penetrating. But the green ones can go in now. The green ones go in because they're going down their own concentration gradient. They're just going to diffuse in because they're penetrating. In they go. What happens to the concentration of the cell as those particles go in? Seriously? Probably if we ended up following this through, would you agree that inside the cell ultimately, we're going to get more concentrated? Do you agree with that? In fact, we probably are going to do something like 0.45 osmolarity inside and outside. We're probably going to be something like 0.15 osmolarity outside because the particles are going to diffuse until they reach their own equilibrium, equal concentration inside and outside. That works for you. The cell itself is now super concentrated. It's way more concentrated inside than it is outside. What's water going to do? This is so beautiful. The water is going to go into the cell. The water is going to move in. What's going to happen to the cell when the water goes in to try and dilute the super concentrated stuff inside the cell? Here's my original cell. Water goes rushing in. You've seen this in Bio 1. No. It explodes. It swells. A cell that swells in a solution, what that means is that the solution is hypotonic. Hypotonic. The solution is hypotonic to the cell. Tonicity is a characteristic that describes what happens to a cell in that solution. If the cell doesn't change, then that is isotonic. Again, review. This is review. Isotonic. No change. What if water leaves the cell? Anyone is it? Hypertonic. Then the solution is hypotonic to the cell because the water leaves and the cell hyperotonic. If the cell shrivels and shrinks, then the solution was hyperotonic to that cell. If the cell swells and expands, then the solution was hypotonic swelling. Oh, very big. Did you fall for that? Tonicity is actually, it doesn't care what the concentrations are. Tonicity depends on whether or not particles are penetrating. And really, all tonicity is a word to describe the solution in comparison to the cell. Now, we can also compare osmolarity. We can use all of our prefixes the same. And we can say, okay, something could be hyposmotic or hyperosmotic or isoosmotic. And in our original scenario, what were the solution to the cell? It was isosmotic. Do you agree with that? Whoa, how'd I get so big? It's isosmotic. If my osmolarity outside, oh, good Lord, you got to be joking me. Where'd I go? How do I make this not happen anymore? Seriously, I have no idea what I hit. Should I try for the escape? Oh, if in doubt, hit escape. Escape. What was I saying? Hey, where am I? Really? There's a lot of stuff that has to happen to get ready for each little piece. Is this going to be one that the YouTubers are going to be like, dude, you got to re-record that one? Tough. I'm not re-recording this. What was I saying? Somebody yell it really loud because they can't remember. I was saying something about hypotonic penetrating. I don't know what I was saying. I know it was important. Isosmotic, that means we're done. Oh, oh, I know what I want to tell you. Please, pretty please be sure to go on top. I love you and you need to read the section on osmosis in some textbook somewhere. Read it because osmosis, I hope that you're feeling a little bit like, oh, really? And you probably are going to want to watch this part of the lecture a couple of times, even though I can't remember what I was going to say at the end. Maybe I will make a discussion board and you'll remind me that it wasn't important, but maybe it wasn't important. Because I think that we have everything that we need. Feeling a little uncomfortable about leaving with something else left to say, but I guess I can always record and add in them. Do you think I'm going to add in them this? There you go. I hope you know now why. Do never mind. I'm just going to leave now. It's been fantastic. And I will see you in five days. Goodbye.