Which statement describes the exhalation process as described in respiration?

• A. Inhalation involves contraction of the diaphragm.
• B. Exhalation occurs during rest due to relaxation of the inspiratory musculature.
• C. Exhalation involves active contraction of the inspiratory muscles.
• D. Oxygen moves out of the bloodstream during expiration.

Answer: (B)

Exhalation at rest is a passive process. When the inspiratory muscles, especially the diaphragm, relax, the elastic recoil of the lungs and chest wall pushes air out, causing the volume inside the thorax to decrease and the air to flow down its pressure gradient. The idea that exhalation involves active contraction of the inspiratory muscles is not true for quiet breathing; such contraction would oppose exhalation and is only seen in forceful expiration, not normal breathing. Also, oxygen moving out of the bloodstream describes a gas‑exchange event that occurs into the tissues, not expiration; during expiration, carbon dioxide is the gas expelled from the body.