 Diffusion is one of the ways to get through directly through the cell membrane, but it's just one of the many. However, those principles of concentration gradients drive everything that we're gonna talk about today. If something goes down the concentration gradient, it is easy, it rolls, it doesn't require any extra energy input because the moving molecules provide the energy to make it happen. All strategies that do not require extra energy input are passive strategies. And I'm gonna summarize all the ways that we get through the cell membrane in this little visual here and then we're gonna go into each specific example. You can imagine if we have a passive approach or a passive set of ways of getting through the cell membrane, we also have active strategies for getting through the cell membrane. Everything will fall into one of those categories. During passive transport, molecules move through the cell membrane because all of this is about going through the cell membrane. They move through the cell membrane down a concentration gradient. Done. Period. Which means what is true about the active strategy? The molecules, molecules move up or against the concentration gradient. I'm gonna put the word against because that's how I describe it. If something moves against the concentration gradient, it's gonna require energy. It's gonna require extra, extra energy. And it's also going to require, it's also going to require a carrier. And maybe I should say here really fast. Carriers, carriers are proteins. And I want to say they're like protein machines that carry things through the cell membrane. Active transport, if you're gonna move something against a concentration gradient, you can't do that directly through the cell membrane. You need a machine to help you do that. That's what a carrier is. It's that machine. Passive transport is different, right? Because we actually have, we already talked about that we don't need no extra energy is needed. And a great question, I should write this down before I move on to the next topic. A great question would be, what is the energy source for passive diffusion? Because there has to be some sort of energy source. It's the kinetic energy of the molecules themselves bumping into each other. And it causes those molecules to spread out and move away from all the other molecules that are like them. So we don't have to put in extra energy. We can just rely on that kinetic energy that they have two types of passive transport. We have simple diffusion. That's just directly through the cell membrane. And that's what we just, we talked about diffusion. Small things and lipophilic things, hydrophobic things can diffuse right through the cell membrane. That's simple diffusion. But we also have facilitated diffusion. Key word here is diffusion because but it's facilitated. So what do you think is true now? We actually have two flavors of facilitated diffusion. You can have facilitated diffusion through a channel, which is like a tunnel, or through a carrier. And guess what? You know I'm going to talk to you about channels, carriers, and the difference between facilitated diffusion carriers and active transport carriers. Not entirely done with active transport because there actually are two kinds of active transport. Both of them require carriers. We have primary, active, transport. And if we had primary, what else do we have? Secondary, active, transport. All active transport requires an energy source because we're moving molecules against their concentration gradient. All active transport requires a carrier protein to move those molecules. Not all passive transport requires that carrier protein. Facilitated diffusion can use a carrier or it can use a channel. And simple diffusion doesn't need anybody. I don't need any help to get through the cell membrane if the thing is small or lipophilic. I have to say I'm slow so I can think through and make sure I've picked the right word. Now we get to look at, I'm going to show you all the things we're going to talk about specifically. We're going to talk about channels. We're going to talk about carriers for facilitated diffusion. Carriers are very similar. Carriers are similar but some of the carriers carry out facilitated diffusion and other carriers do primary active transport and secondary active transport. So we have four topics that we're going to talk about that this framework is going to frame for us.