Final answer:
Ventilation is the process of moving air into and out of the alveoli, while perfusion affects the flow of blood in the capillaries. External respiration occurs in the alveoli, while internal respiration occurs in the tissue. The correct option is D.
Step-by-step explanation:
Ventilation is the process that moves air into and out of the alveoli, and perfusion affects the flow of blood in the capillaries. Both are important in gas exchange, as ventilation must be sufficient to create a high partial pressure of oxygen in the alveoli.
If ventilation is insufficient and the partial pressure of oxygen drops in the alveolar air, the capillary is constricted and blood flow is redirected to alveoli with sufficient ventilation.
External respiration refers to gas exchange that occurs in the alveoli, whereas internal respiration refers to gas exchange that occurs in the tissue. Both are driven by partial pressure differences. The correct option is D.