What defines the process of respiration in the respiratory system?

The process of respiration in the respiratory system is defined by the exchange of gases between air and blood. This fundamental process involves inhaling oxygen from the atmosphere into the lungs, where it diffuses into the bloodstream. Simultaneously, carbon dioxide, which is a waste product of cellular metabolism, is released from the blood into the air within the lungs, allowing it to be exhaled. The efficient exchange of these gases is crucial for maintaining adequate oxygen levels in the body and removing carbon dioxide, thereby supporting cellular respiration and overall metabolic functions.

The other choices pertain to different physiological processes. The absorption of nutrients is related to digestion rather than respiration, while the breakdown of food occurs in the digestive tract and is not part of gas exchange. Although filtering of air is a function of the respiratory system, as it helps to clean the air of particulates before it reaches the lungs, it does not encompass the essence of respiration, which is specifically about gas exchange. Thus, the accurate definition of respiration focuses on the exchange of gases between air and blood.