 hope you don't feel like I'm repeating myself a bajillion for a million times today. I'm kind of feeling like I'm repeating myself a bajillion for a million times today but don't forget secondary active transport requires energy and it requires a carrier and it moves molecules against the concentration gradient and it requires energy to do this and if you had to take a wild guess if I said true or false right now you're gonna bet whatever dessert you're having tonight you're betting that put it on the table if you get this right you get the dessert if you get it wrong I get the dessert here's the true false question is this true or false secondary active transport needs energy in the form of ATP true or false what are you gonna say all right I just have to say some words here about this I just posed a question to you that you don't know the answer to you don't know if you don't know what the energy source is you know we need energy but you don't know what the energy source is and I just said is it ATP and if you had to guess right now I'm gonna say you should say no it's not ATP that would be a good guess because if it was ATP how's it different from primary active transport that's the logic I just walked you through a logic thing that you can do on a test if you are faced with something that you're like what I've never heard this before in my life you could actually figure it out sometimes not all the time but sometimes you can't it's true secondary active transport doesn't use ATP are you ready to go with me on this instead it uses a concentration gradient of another molecule okay what are you serious it's like hitching a ride one molecule when you have secondary active transport one molecule moves down its concentration gradient and the carrier uses the energy from that molecule moving down its concentration gradient it captures the energy in that movement and uses that energy to pump something else against its concentration gradient the rule of thumb is if you don't see ATP involved there probably is some molecule going down its concentration gradient and that's how that's where the energy is coming from for this secondary active transport you can think of it like one molecule is catching a ride with another molecule that's going down its concentration gradient you just you just hitch a ride you're already going that way I don't have to pay for the gas because you already have it right so ultimately if I were to ask the question does secondary active transport rely on ATP I say this from experience I have asked that question and I have expected the answer to be no it does not and then I get baffled when students complain about they thought it did and if they thought it did because somewhere you had to have ATP to establish somebody else's concentration gradient that they came down did you follow that crazy line in secondary active transport someone has a concentration gradient that they traveled down but how did we get that concentration gradient somewhere a primary active transporter used ATP to create that concentration gradient secondary active transporters I can't think of a secondary active transporter that exists on its own it has to be coupled with a primary active transporter in order to establish that concentration gradient in the first place how do you feel about this remember we're just dealing with carriers we don't have active transport through channels we don't have active transport directly through the cell membrane but we do have carrier proteins that do the do the job one more way that we can move trickier molecules through the cell membrane and that's vesicular transport which we're going to talk about in a second