To understand where ATP fits into the picture, one must first understand the mechanics of the transport protein itself.

It’s a fair question. Primary active transport (like the sodium-potassium pump) clearly uses ATP. Passive transport uses no energy at all. Secondary active transport sits in the middle—and that’s where the confusion begins.

The is the archetype of primary active transport. It sits on the plasma membrane and performs the following cycle:

It comes from a gradient that was created by primary active transport—which does use ATP.

The energy doesn't come from a fresh spark of ATP at the moment of transport; it comes from the potential energy of the gradient that was already built by ATP earlier. The Two Types of Secondary Active Transport