What does external respiration primarily involve?

External respiration is primarily concerned with the processes that occur in the lungs, where the body exchanges gases with the environment. This involves breathing in oxygen (inhalation), which is then diffused into the bloodstream, and simultaneously releasing carbon dioxide from the blood into the lungs to be exhaled. This vital exchange is crucial for maintaining proper oxygen levels in the blood and removing waste gases.

In contrast, the other options relate to different aspects of respiration or physiological processes. For example, gas exchange between blood and tissues pertains to internal respiration, which occurs at the cellular level rather than in the lungs. The production of energy through cellular respiration is a metabolic process that occurs in cells and utilizes the oxygen delivered through external respiration, while the transportation of oxygen through the bloodstream primarily refers to the function of the circulatory system after gas exchange has occurred in the lungs.