Instead, what they do is they use an established electrochemical gradient of one molecule to move a different molecule against its electrochemical gradient. So we see that they couple non spontaneous flow of one molecule or ion with a spontaneous flow of a different molecule or ion. So we have two types of secondary transporters. We have antiporters, also known as exchangers, and we have Simporters, also known as co transporters. So let's begin by focusing on antiporters. And let's take a look at this diagram.