Here's why:

* Mitochondria are the powerhouses of the cell. They are responsible for producing ATP, the cell's primary energy currency.

* Cellular respiration is the process that occurs in the mitochondria to generate ATP.

* Oxygen is the final electron acceptor in the electron transport chain, a key step in cellular respiration. Without oxygen, the electron transport chain cannot function, and ATP production significantly decreases.

While other cell structures may indirectly be affected by the lack of oxygen (like the Golgi apparatus which relies on energy from ATP), the mitochondria is the only structure that directly requires oxygen for its primary function.