* Active transport moves molecules against their concentration gradient. This means moving molecules from an area of low concentration to an area of high concentration. This requires energy because it goes against the natural flow of diffusion.

* ATP is the primary energy currency of cells. It stores chemical energy that can be released when needed to power cellular processes.

* Active transport proteins use ATP to change their shape. This shape change allows them to bind to the molecule being transported and move it across the cell membrane.

Here's a simple analogy: Imagine you're trying to push a ball uphill. This is like active transport - you're working against gravity. To do this, you need energy, like eating a sandwich (ATP). The sandwich gives you the energy to push the ball uphill, and the active transport protein uses ATP to move molecules against their concentration gradient.

Let me know if you have any more questions!