What is the primary gas exchanged during respiration?

The primary gas exchanged during respiration is oxygen. In the process of respiration, particularly during cellular respiration, organisms take in oxygen from their environment and use it to produce energy. This occurs when oxygen is inhaled into the lungs, where it diffuses across the alveolar membrane into the bloodstream. Once in the blood, oxygen binds to hemoglobin molecules in red blood cells and is transported to cells throughout the body.

While carbon dioxide is also involved in the respiratory process, as it is the waste product produced from cellular respiration and is expelled from the body, it is not the primary gas that is exchanged. Ozone is a gas found in the atmosphere, primarily in the stratosphere, and does not play a direct role in the respiratory exchange process. Nitrogen, while abundantly present in the air we breathe, is largely inert and does not participate in the gas exchange necessary for respiration. Therefore, oxygen is accurately recognized as the primary gas exchanged during respiration.