Here's why:

* Catabolism is the breakdown of complex molecules into simpler ones, releasing energy in the process. Mitochondria are the powerhouses of the cell, responsible for cellular respiration, which is a catabolic process.

* Cellular respiration involves breaking down glucose (a complex sugar) into carbon dioxide and water, releasing energy in the form of ATP (adenosine triphosphate). This ATP is then used by the cell for various functions.

* Anabolism, on the other hand, is the building up of complex molecules from simpler ones, requiring energy input. While mitochondria indirectly contribute to anabolism by providing the energy needed for these processes, they are not directly involved in the building up of molecules.

In summary: Mitochondria are crucial for catabolism, specifically for the energy production through cellular respiration.