We exhale carbon dioxide (CO2) as a result of cellular respiration. This process occurs in the mitochondria of our cells, where glucose and oxygen react to produce energy, water, and carbon dioxide. The carbon dioxide generated is then transported through our bloodstream to the lungs, where it is expelled when we breathe out. It is essential to remove this waste product to maintain proper acid-base balance in the body, and excessive buildup can lead to respiratory issues. Breathing in oxygen and exhaling carbon dioxide is crucial for the overall function of living organisms.