 So active transport pumps molecules against the concentration gradient and requires an energy source in order to do so. We have two forms of carrier mediated active transport. We have primary active transport and secondary active transport. Let's talk about primary active transport first because dude, we drew a picture of it right here. All we have to add to this picture is some way for this transporter to use energy to make that happen. The most common form of energy that your body has going on for it is ATP. If we throw a molecule of ATP onto this transporter, onto this carrier protein, the ATP, the energy stored in the ATP molecule can be transferred to the carrier protein. The carrier protein can use that energy in the ATP molecule to pump the item, to pump the solute against the concentration gradient and into the intracellular fluid where you're like, dude, we already have a ton of it in there. Remember, ATP, where does it come from? It comes from the process of cellular respiration, which takes place in the mitochondria in all of your cells. ATP is made from glucose or other food items that are energy providing. So you take a glucose molecule, you break it down and do all this crazy stuff. Thank you, mitochondria. And you end up with molecules of ATP that your body can use to carry out whatever its functions are that are necessary. Active transport, primary active transport requires ATP to pump things, molecules, against their concentration gradient. You will see quite soon that this is actually super important for physiological function. Okay, that's primary active transport. Very straightforward, nice, easy, that's easy. Secondary active transport. I've actually drawn you a little picture here of secondary active transport because I want you to be able to visualize like secondary active transport is weird. Do you agree that I pumped, I used ATP to pump all these little purple particles into the intracellular fluid. This is still the intracellular fluid. So you're cool with that, right? So I'm just going to use this exact same scenario. Do you agree that we now have a concentration gradient of purple particles? Of course we do. We used ATP to create that concentration gradient. In secondary active transport, we're going to use the energy in the concentration gradient to pump new molecules against their concentration gradient. So I am going to use the energy in this concentration gradient to get rid of these little few red particles to pump them out. Pumping them out would be hard, right? That's against the concentration gradient. But pumping out the purple particles, is that going to be hard? No, doggies, they want out. There's so many purple particles in here. We are not having any fun anymore. Let us out. We want to go see the world. And okay, so let's see, let's let them out. In the process of letting them out, let's see if we can hitch a ride for the red particle too and pump it against its concentration gradient. That's secondary active transport. You can imagine that this little transporter has a binding site for the purple particle. Once the purple particle binds, it's going to want to bind. There's jillions of them in there. Once it binds, a binding site for the red particle is going to open up. If you don't have a purple particle attached, you're not going to have an opening or a binding site, but a chair for the red particle doesn't exist because you don't have a purple particle to make it happen. But once that purple particle is there, it opens up, it confirmation change, and now the red particle is literally, once we've got both of them attached, we're going to change that confirmation and we're going to dump both of them out. We're going to dump out the purple one. We're going to dump out the red one. The confirmation change causes, since you got rid of those guys, you're going to flip back to your original confirmation. That's an example. That's a general idea. The bottom line is that this process relies on the concentration gradient of another molecule to pump somebody against the concentration gradient. So it indirectly requires ATP to make it happen, which is why it's classified as an active transport process. We also have vesicular transport and I've got a couple pictures for you of what that is because it's kind of hard to visualize and certainly hard for me to draw. Vesicular transport means we're making vesicles. We're making vesicles to get stuff out of the cell or we're using vesicles to get stuff into the cell and endocytosis is bringing stuff in. This is cell membrane right here. You can see that the cell membrane is just going to go around and engulf any item. Phagocytosis is engulfing a solid particle in the extracellular fluid and pulling it in. The particle literally gets engulfed in cell membrane and that cell membrane like pinches off inside the cell and you have a little vacuole, a little bubble of cell membrane that has the particle inside of it. Once you have that bubble of cell membrane inside the cell, you can do stuff with it. You can digest it. You can break it apart. You can put it on your Facebook page. You can do whatever you want with it. I'm not joking. You can bring in fluid, awesome, or you can bring in like other things that stick to specific receptors. Sometimes like a bad guy, a bacterium is going to have a certain receptor that will stick to or a certain molecule that will stick to a certain receptor and that initiates the process of endocytosis or phagocytosis, yumpscialization if you like. Endocytosis bringing stuff into the cell. Exocytosis is barfing stuff out of the cell in the opposite. So you can imagine here's a little vesicle and we're going to come up and the cell membrane literally fuses. The vesicle cell membrane fuses to the cell membrane and then you end up with a bigger cell membrane and you barfed the substance that was inside the vesicle out into the cell membrane itself. And here's another like, wow, this is a lovely picture. I don't know. Is this endocytosis or exocytosis? You see how it could be either depending on whether we're pinching off that vesicle and sending it in or we are letting that vesicle dump its goods out into the extracellular fluid. Either way, what a lovely beautiful picture and a nice visual of the process. Requires energy. That vesicular transport requires energy to get stuff in and out, otherwise it's considered active transport but it doesn't require a carrier. So it isn't carrier based. I feel like I already said that. Did I already say that to you at some point in this lecture? Okay. We've gotten substances in and out and now we have to talk about water and if you need to, take a break and get some water and maybe some chocolate because I'm telling you what's coming next requires some focus. You focus me, I'm fine. We're going to talk about osmosis next.