Here's why:

* Mitochondria are the powerhouses of the cell. They are responsible for producing the majority of the cell's ATP.

* ATP is the primary energy currency of cells. It's like a tiny battery that stores and releases energy for various cellular processes.

* Mitochondria break down glucose and other nutrients through cellular respiration. This process involves a series of chemical reactions that ultimately generate ATP.

So, while mitochondria do not directly "release" energy in the way we think of it, they generate ATP, which is the molecule cells use to power their functions.