 I know you're not going to believe this, but there's actually something I forgot to tell you. I forgot to tell you that in chemistry, you measure things in molarity. That's the concentration that you use. And in fact, in our lab coming up this week on osmosis, wait for it, it'll be fun. Most of the concentrations of solutions that we're going to be dealing with in that lab are measured in molarity. And you'll actually see that. You'll see a .3 molar solution of this. In physiology, in bodies, molarity is not as informative as a concept called osmolarity. So we can actually measure the osmolarity of a substance. And this is something that you definitely want to feel good about. Osmolarity is not just the moles of a substance. It actually is the number of particles. Particles per mole, or per molecule per mole. Particle, can you even read that? That says particles. Particles per mole. Okay, so look at this for a second. Let's look at something like sodium chloride. Sodium NaCl. Sodium chloride is a substance that if you look at it, we could say, okay, I have one mole of sodium chloride molecules. But here's an amazing thing about sodium chloride. When you put it in water, it actually splits. And it turns into sodium ions and chloride ions. I'm going to expect you to know that sodium chloride, if you dump it into water, it's going to dissociate in water. And it's going to become two separate molecules. Sodium chloride dissociates in water. I'm going to give you an example of a molecule that does not dissociate in water with that molecule. Glucose. Glucose does not split into a different number of particles. It doesn't split into six, I mean, this would be 24 atoms. We don't get 24 particles when we stick a glucose molecule into water. It actually stays one glucose molecule. So if you put a mole of glucose into a solution, you're going to end up with a mole of particles. Does that work for you? If you put a mole of sodium chloride into a solution, one mole goes in. What do we have at the end? It dissociates in water. So now we have two moles of particles. You follow that? You need to know that sodium chloride dissociates in water. Beyond that, if you want to ask me, and you need to know that glucose does not. Other than that, ask. If I am asking you for the concentration of a solution and you're not sure if it dissociates in water or not, go ahead and just ask me. And then I can help you out because some things do dissociate in water and many things do not. If you want to know the osmolarity of a one molar solution of sodium chloride, that's actually two osmols. Do you see that? Because we have two particles that it breaks into. And one molar solution of glucose is one osmol. Excuse me. And in your cell, this is a cool fast fact. I'm running out of room. I'm going to draw a cell down here and I'm going to draw it in green because I don't think I've used green yet. So this is a cell doing its thing. Guess what the concentration of your intracellular flume it is. It's about 280 milli osmols. Does that work for you? 0.28 osmols. Sometimes we just round that up to 0.3 osmols and that's 300 milli osmols. Those are just the concentrations of your intracellular fluid. Now, the whole point that we were going to talk about in this part of the lecture is that diffusion happens if you have concentration gradients. So let's take a look at this visual right here. Remember we decided that this was super concentrated? Wow, that's really pretty. This is very low concentration. And so does it make sense that molecules are actually going to move down the concentration gradient? I could put a number on this. I could tell you that this was like four osmols and this was like 0.1 osmol. And now we've got numbers that say, yeah, that's super concentrated. That's not very concentrated at all. And now you can imagine that, yeah, those molecules are going to move down the concentration gradient. Of course they are. So take a look here at this little GIF thing. I think it's going to start over. Hold on, it's going to start there. Now it's super concentrated here, but these molecules, all they're doing is randomly moving. And that random motion, I know you did this. I know you did like the carmine red powder moving all around the beetles. Remember in Biowan, those little molecules just were like, moving, that's brownie in motion. They move like that, molecules move. They have a random kinetic energy that causes them to just move like that. And just by that random motion, they move from areas of high concentration to areas of low concentration. That's diffusion. Now, visualize. Stop, collaborate and listen. If you visualize a new, oh, holy stop. Sorry about that. And then you got to bust out some MC Hammer. Really? Is that MC Hammer? Oh my gosh, I only have one more little lecture to do. You only have to go through this for one more little lecture. If I had some kind of wall between these two compartments, then it would matter if my molecules, I could actually put some kind of membrane between those. And if that molecule couldn't go through, then diffusion wouldn't happen through that little compartment. Does that work for you? Like, that's kind of logical. It makes sense. All right, molecules move from high concentration to low concentration. Take a deep breath and let's talk about osmosis. Osmosis is the movement of water.