Inhalation is the active process drawing air into the lungs.

• A. Active Process Drawing Air Into The Lungs
• B. Passive Process Expelling Air
• C. Active Process Expelling Air
• D. Passive Process Drawing Air Into The Lungs

Answer: (A)

Inhalation is an active process that draws air into the lungs because it relies on skeletal muscle contraction to expand the thoracic cavity. When the diaphragm contracts, it moves downward, and the external intercostal muscles lift the ribs, increasing the volume of the chest. This larger volume lowers the intrapulmonary pressure below atmospheric pressure, so air flows into the lungs until the pressures equalize. The energy needed comes from muscle work, which is why this phase is considered active.

At rest, exhalation is typically a passive process driven by the elastic recoil of the lungs and chest wall, not muscle contraction. Forced exhalation, in contrast, uses the internal intercostal and abdominal muscles to actively push air out. This helps distinguish inhalation from exhalation and explains why drawing air into the lungs is classified as an active process.