Which phase of respiration involves the physical act of breathing?

The phase of respiration that involves the physical act of breathing is ventilation. This process includes the mechanical movements that allow air to flow in and out of the lungs, specifically through inhalation (the intake of air) and exhalation (the expulsion of air). During ventilation, oxygen is drawn into the lungs, where it will later diffuse into the bloodstream, while carbon dioxide is removed from the blood and expelled from the body.

In contrast, diffusion refers to the movement of gases (oxygen and carbon dioxide) across the alveolar membrane, allowing for gas exchange without the active process of breathing. Utilization pertains to the way cells use oxygen for metabolic processes, and although critical to respiration, it does not involve the physical action of breathing. Transportation involves the movement of gases within the bloodstream from the lungs to the tissues and back, which again does not encompass the act of breathing itself. Therefore, the correct option that describes the physical act of breathing is ventilation.