Which process involves the exchange of O2 and CO2 between an organism and its environment?

The process that encompasses the exchange of oxygen (O2) and carbon dioxide (CO2) between an organism and its environment is respiration. This physiological process includes not only the mechanical act of breathing but also the biochemical processes that occur at the cellular level, where O2 is utilized for metabolism while CO2, a byproduct of this process, is expelled.

Respiration can be divided into external respiration, which involves the exchange of gases in the lungs or gills, and internal respiration, which is the exchange of gases at the cellular level. This comprehensive process ensures that organisms obtain the necessary O2 for cellular function and remove CO2 to maintain homeostasis and prevent toxicity. The other choices, though related to biological processes, do not encapsulate the entirety of gas exchange in the way respiration does. For instance, ventilation refers specifically to the mechanical movement of air in and out of the lungs but does not include the chemical processes associated with gas exchange. Thus, respiration accurately describes the full scope of O2 and CO2 exchange in the organism along with its interaction with the environment.