Here's why:

* Cellular Respiration: Mitochondria are the powerhouses of the cell, where cellular respiration takes place. This process uses oxygen (O2) to break down glucose and produce energy (ATP).

* Carbon Dioxide Production: As a byproduct of cellular respiration, carbon dioxide (CO2) is generated.

* Gas Exchange: The inner membrane of the mitochondria has a large surface area, allowing for efficient exchange of oxygen and carbon dioxide between the mitochondria and the surrounding cytoplasm.

Important Note: While mitochondria are responsible for gas exchange within the cell, they are not the primary organs involved in gas exchange for the entire organism. That role belongs to the lungs in animals and leaves in plants.