Here's why:

* Active transport requires energy to move molecules against their concentration gradient, meaning from an area of low concentration to an area of high concentration.

* ATP is the primary energy currency of cells. It stores chemical energy in its phosphate bonds.

* When a phosphate bond is broken, energy is released, which can be used to power active transport pumps. These pumps bind to the molecules being transported, use the energy from ATP hydrolysis, and move them across the membrane.

Examples of active transport processes that require ATP:

* The sodium-potassium pump (Na+/K+ pump)

* The proton pump

* The glucose transporter in the intestines

Let me know if you'd like more information on active transport or ATP!