Here's why:

* Mitochondria are the powerhouses of the cell: They are responsible for cellular respiration, the process that converts the chemical energy stored in sugars (like glucose) into ATP, the cell's main energy currency.

* Cellular Respiration: This process occurs in three main stages:

* Glycolysis: This occurs in the cytoplasm and breaks down glucose into pyruvate.

* Krebs Cycle (Citric Acid Cycle): This occurs in the mitochondrial matrix and further breaks down pyruvate to produce electron carriers (NADH and FADH2).

* Electron Transport Chain: This occurs in the inner mitochondrial membrane and uses the electron carriers to generate a proton gradient that drives ATP production through ATP synthase.

So, while sugars are initially broken down in the cytoplasm, the mitochondria are essential for the final stages of ATP production.