Here's why:

* Mitochondria are the powerhouses of the cell. They are responsible for cellular respiration, the process that breaks down glucose (sugar) and converts it into ATP (adenosine triphosphate), the primary energy currency of cells.

* ATP fuels all the cellular processes that require energy, such as muscle contraction, protein synthesis, and active transport.

While other parts of the cell play roles in metabolism, the mitochondria are the primary site of energy production.