What is defined as the exchange of gases between the atmosphere and the blood?

The exchange of gases between the atmosphere and the blood is specifically referred to as external respiration. This process occurs in the lungs, where oxygen is inhaled into the air sacs (alveoli) and diffuses into the blood, while carbon dioxide diffuses from the blood into the alveoli to be exhaled. External respiration is crucial for maintaining the body's oxygen levels and removing carbon dioxide, which is a waste product of metabolism.

In contrast, internal respiration refers to the exchange of gases between the blood and the cells throughout the body. Cellular respiration is the process by which cells use oxygen to produce energy from glucose and produce carbon dioxide as a byproduct. Photosynthesis is a process used by plants to convert light energy into chemical energy, utilizing carbon dioxide and water to produce glucose and oxygen, but it does not pertain to gas exchange in animals. Thus, external respiration is the correct term for the exchange of gases between the atmosphere and the blood.