What occurs during external respiration?

• A. Exchange of gases in the cells
• B. Diffusion of gases between alveoli and blood
• C. Inhalation and exhalation process
• D. Regulation of carbon dioxide levels

Answer: (B)

During external respiration, the primary event is the diffusion of gases between the alveoli and the blood. This process occurs in the lungs, where oxygen from the inhaled air passes through the alveolar walls and enters the bloodstream, while carbon dioxide from the blood diffuses into the alveoli to be exhaled. This gas exchange is crucial for maintaining the balance of oxygen and carbon dioxide in the body, ensuring that tissues receive the oxygen they need for metabolism and that carbon dioxide, a waste product of metabolism, is removed efficiently.

In contrast, the other choices describe different processes related to respiration or circulation. The exchange of gases in the cells refers to internal respiration, not external. The inhalation and exhalation processes involve the mechanical aspect of breathing but do not specifically address the gas exchange that characterizes external respiration. Regulation of carbon dioxide levels involves the metabolic and respiratory processes but is not a direct description of what happens during external respiration itself.