What occurs during external respiration?

During external respiration, gas exchange occurs between the alveoli in the lungs and the surrounding capillaries. This vital process involves the diffusion of oxygen from the alveoli, where it is in high concentration, into the capillaries, where it is at a lower concentration. Simultaneously, carbon dioxide, which is in higher concentration in the capillaries due to cellular metabolism, diffuses into the alveoli to be exhaled. This exchange of gases is crucial for maintaining the body’s oxygen levels and removing carbon dioxide, which is a waste product of cellular respiration.

The other options describe different physiological processes. Oxygen transport to cells pertains to the circulatory system, where oxygen is carried by hemoglobin in red blood cells to various tissues. Energy production in cells refers to cellular respiration, a biochemical process within cells where oxygen is used to convert glucose into energy. Air movement in the trachea is related to the mechanics of breathing, but it does not involve the exchange of gases that is characteristic of external respiration.