So another important category of membrane pumps are the secondary transporters. And as we'll see in just a moment, there are two types. So we see that secondary transporters are these transmembrane pumps that do not actually break down ATP molecules directly. 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.