Here's why:

* Cellular Respiration: Your cells use oxygen to break down food for energy. This process produces carbon dioxide as a waste product.

* Blood Transport: Carbon dioxide enters the bloodstream and travels to the lungs.

* Lung Exchange: In the lungs, carbon dioxide diffuses from the blood into tiny air sacs called alveoli.

* Exhalation: When you exhale, the carbon dioxide is released from your body.