 Hey everybody, Dr. O here. This is the first video of several videos where I'm going to talk about the ways that things move into and out of cells. So the three key things we're going to talk about are going to be diffusion, osmosis and active transport. We'll cover some more things and we're just going to cover diffusion really in this video. But I want to talk about all three of those. I like to put them in context by talking about them amongst each other. So diffusion is when you move solutes from an area of high to low concentration. Osmosis is when you move water, which is the solvent from a high to low concentration, or the simplest way to think about osmosis is water following solutes. And active transport is going to move solutes, but it's going to move it against the concentration gradient from an area of low concentration to high. So notice how they're very similar. Diffusion thinks solute from high to low concentration. Active transport thinks solute from low to high concentration. And because that requires energy, that's why it's called an active process. It does require ATP. And then osmosis, still a passive process, but instead of the solute moving, the solvent, which is water, is moving. So it'll make more sense when we go through all three of them, but I like to compare and contrast the three right in one place. All right. So let's go ahead and look at diffusion. We'll start with simple diffusion. Diffusion is the movement of solute from an area of high to low concentration. So as you can see from this image, there's a whole lot of solute outside of this cell membrane, very little on the inside. So diffusion is going to make it want to move in there. So why? First of all, all molecules are constantly in motion and they're colliding with one another. Even the molecules in a glass of water at room temperature are moving near 1,400 miles per hour. So there's going to be a lot of collisions. So if you have an area where there's an area of really high concentration, they're going to collide more often, which is why they're going to spread apart. Best analogy I can give you is a jumper. Imagine we were all in a classroom together, 30 of us in a room, and they gave everyone a jump rope, and we were all standing in one corner and started jumping rope. What would happen? We'd start whipping the bejesus out of each other, and we would move. We would spread away. So those molecular collisions cause us to spread out. So that's my favorite example. Other examples, real world examples, if you spray perfume or some sort of ascent in a room, it's going to spread throughout that room from an area of high concentration where you actually originally sprayed it as it travels through the room, and then it's going to diffuse through the room. Those will do the same thing. All sorts of things are going to diffuse. So if things are moving from where there's a lot of it, area of high concentration to low concentration, this is going to be diffusion. So simple diffusion can, and obviously we can speed this up, right? If you're going to make a solution of Kool-Aid, you're going to pour in the sugar and the packet of Kool-Aid, you're going to stir it. That's how you're going to speed that up. Or think tea. You've got, when you put a tea bag in hot water, all the tea is in the tea bag, and it diffuses out into the cup. So if the water is hot, that process is going to happen a lot faster. So you can certainly speed up diffusion by increasing temperature or mechanical stirring, these kind of things. So this is diffusion, this simple process where things move from an area of high to low concentration. So that's going to be simple diffusion. It is a passive process, meaning it does not require any energy. This image shows the same thing, but it says they're small, uncharged molecules. So especially things that are lipid soluble and can travel right through the cell membrane that are small and don't have a charge. They're going to be able to diffuse right through the cell membrane. That's what simple diffusion is. So imagine your gasses. We'll talk a lot about carbon dioxide and oxygen later. These gasses are a perfect example. Oxygen diffuses from the lungs, where there's a lot of it, into your blood where there isn't very much of it. Carbon dioxide, at least in your lungs. Carbon dioxide diffuses the other direction because there's more carbon dioxide in the blood coming back to your lungs than there is inside of them. So that's going to be simple diffusion, but it's not always that simple. They're large, or they're nonpolar, or they're charged, so they can't just travel right through the cell membrane. That's where you're going to have facilitated diffusion. So facilitated diffusion is still a passive process, does not require energy. But here you see an example. Glucose can't just travel through the cell membrane, so it's going to be carried by the glucose transporter, which is an example of a carrier protein. It's going to be carried into your cells with this carrier protein. And then here you see these protein channels. So sodium, same thing. Sodium can't travel right through the cell membrane, so it's going to travel through this protein channel so that it's still diffusion, so the movement from high to low concentration. It's still passive, but in these examples, facilitated diffusion, you're going to need either a protein channel or a protein transporter to do the job for you. So that is diffusion, the movement of solute from an area of high to low concentration. I hope this helps. Have a wonderful day. Be blessed.