The term for the physiological process of bringing in oxygen and expelling carbon dioxide is respiration. This process occurs in living organisms to facilitate cellular metabolism, where oxygen is used to convert nutrients, primarily glucose, into energy while producing carbon dioxide as a byproduct. Respiration can be categorized as aerobic (requiring oxygen) or anaerobic (occurring without oxygen). This essential function supports bodily functions, including energy production and waste removal. Understanding respiration provides insights into cellular activity and the physiological processes that sustain life.