D → A → C → B → E

D. Atmospheric air is drawn into alveoli and CO₂-rich alveolar air is released out into the atmosphere (pulmonary
ventilation).

A. Across alveolar membrane, O₂ diffuses into the blood in the pulmonary capillaries and CO₂ diffuses into the alveoli from the blood (pulmonary gas exchange).

C. Blood transports oxygen from the lungs to the tissues (and carbon dioxide from the tissues to the alveoli).

B. O₂ diffuses from the blood in the systemic capillaries into the systemic tissues and CO₂ diffuses from the tissues
to the blood (systemic gas exchange).

E. The cells utilise O₂ for catabolic reactions, resulting in the release of CO