 Hey everybody, Dr. O here. So we've talked about diffusion, which is where solutes move from an area of high to low concentration. Passive process does not require energy. We've talked about osmosis, which is where water moves from where there is a high concentration of water to a low concentration. So that's the solvent moving. Now we're going to talk about active transport. So active transport is really the opposite direction of diffusion. It's the movement of solutes from where there's a low concentration to where there's already a high concentration. This is called active transport because all active processes require ATP. So this is the only one that requires energy. So here you see the best example of active transport in the human body. This is what's known as the sodium-potassium exchange pump. So what this is going to do, you see at the bottom there, as ATP is being used, for every ATP being used, three sodiums are going to be pumped outside of your cells where there's already a lot of sodium, and two potassiums are going to be pulled into your cells where there's already a lot of potassium. So they're moving against their concentration gradients from low to high concentration. So you're forcing these things uphill, which is why they require energy. This is such a big deal because if you can't keep sodium outside of your cells, then your nerves can't turn on. If you can't keep potassium inside your cells, then your nerves can't turn off. So super, super important in all cells, but especially so in your nervous system. 40% of the ATP your brain's going to use today is going to be used to power this pump so that all your neurons can keep doing their job. This is why, as we'll learn later, that a resting nerve or a nerve that's ready to depolarize has a charge of negative 70 millivolts because you're pulling more positive sodium out of the neuron than you're replacing with positive potassium. So that's the sodium-potassium exchange pump, a great example of active transport. Where else would you need it? So this is the biggest example for sure, but active transport pumps are also going to pump hydrogen ions into your stomach, so your stomach is full of acid, so there's already a lot of hydrogen ions in there, but as you're digesting food, as your body churns in, you know, creates more stomach juice and adds more hydrogen ions, you're going to be pumping even more of them to where there already is a lot. So that'd be another example of active transport. But the sodium-potassium exchange pump is by far the most important example of active transport. That requires energy moving solute from low to high concentration. All right, I hope this helps. Have a wonderful day. Be blessed.