Oxygen will diffuse out of blood during the phase of respiration called:

A. Exhalation is the passive phase of normal breathing and occurs without effort during relaxed respiration. It involves the diaphragm and intercostal muscles relaxing, allowing air to flow out of the lungs.
B. Apnea refers to a temporary cessation of breathing and is not a phase of normal breathing.
C. Inhalation is the active phase of normal, relaxed breathing. It requires energy as the diaphragm contracts and moves downward and the intercostal muscles contract to expand the chest cavity, allowing air to enter the lungs.
D. Expiration is another term for exhalation, which is passive during normal relaxed breathing.

A. The external exchange of gases refers to the process of oxygen diffusing from the alveoli into the blood and carbon dioxide diffusing from the blood into the alveoli in the lungs. This occurs during pulmonary ventilation.
B. Pulmonary ventilation involves the movement of air in and out of the lungs (breathing), not the exchange of gases.
C. The internal exchange of gases refers to the diffusion of oxygen from the blood to the tissues and carbon dioxide from the tissues to the blood. This happens at the cellular level throughout the body.
D. This answer is incorrect because internal exchange of gases is the correct phase for oxygen to diffuse out of the blood.