Here's why:

* Mitochondria are often referred to as the "powerhouses" of the cell. They have a specialized structure with two membranes (outer and inner) that create compartments essential for the different stages of respiration.

* Glycolysis, the first step of respiration, takes place in the cytoplasm of the cell.

* However, the remaining steps (Krebs cycle and electron transport chain) occur within the mitochondria. The inner membrane of the mitochondria is particularly important for the electron transport chain, which generates the majority of ATP (adenosine triphosphate), the energy currency of the cell.

Let me know if you'd like more detail on any of these steps!