 Carrier proteins are actually involved, check this out. We have carrier proteins involved in active transport, and we have carrier proteins that are involved in diffusion, in facilitated diffusion. So what is a carrier? Well, these are the guys that I drew that I draw them like this, because I envision if this is my cell membrane, this is one carrier. So this is moment one, that I have a carrier that is open to the extracellular fluid, and here is the intracellular fluid. And then at moment two, for some reason, the carrier has a conformational change, a shape change, oh geez. And now the carrier is open to the intracellular fluid. You can imagine that if I had a substance like this substance right here, it's actually the binding of the substance to the carrier protein that initiates the shape change. The shape changes, the confirmation changes, and then the confirmation change literally dumps changes where the opening is. The opening started to the extracellular fluid, molecule bound, shape changes, now the opening is to the intracellular fluid and the molecule falls off. We've now transported the molecule from the extracellular fluid into the intracellular fluid. Once the molecule falls off, usually the shape will go back to its original confirmation because that molecule isn't attached to it anymore. In its original confirmation, it waits for another molecule. And this is something that, I don't know, I find it like, this class is so cool. The fact that these molecules, literally, molecules sticking together cause molecules to change shape and it's the shape change that enables function. It's the change in the structure that affects how that molecule is actually going to function in the body, a pattern that we will see over and over again because that's literally how everything works. Now, if you know that molecules, that these carriers can enable facilitated diffusion or active transport, what is the difference? Like, how are you going to know if this is facilitated diffusion or active transport? An easy, peasy way of knowing. Are we pumping molecules against the concentration gradient or are we pumping them with the concentration gradient? Okay, so I'm going to make this into either passive, I mean facilitated diffusion or active transport. Are you ready? This is what I'm doing. This is like this. Did we pump that thing with the concentration gradient or against the concentration gradient? So higher concentration in the intracellular fluid, we moved a particle from the extracellular fluid into the intracellular fluid, that's against the concentration gradient. We're pumping something into its higher concentration zone, which means that has to be an example of active transport. So active transport is what we're talking about next.