Here's why:

* Cellular Respiration: Mitochondria are the powerhouses of the cell, and they are responsible for cellular respiration. This process breaks down glucose (a sugar) in the presence of oxygen to produce energy in the form of ATP.

* Glycolysis: While glycolysis, the initial step of sugar breakdown, occurs in the cytoplasm, the subsequent steps of cellular respiration occur within the mitochondria.

* Krebs Cycle and Electron Transport Chain: The Krebs cycle and the electron transport chain, which take place inside the mitochondria, are crucial for generating the majority of ATP from sugar.

Let me know if you have any other questions!