Which statement accurately describes inhalation and exhalation?

• A. Inhalation Is Passive And Exhalation Is Passive
• B. Inhalation Is Active; Exhalation Is Passive
• C. Inhalation Is Passive; Exhalation Is Active
• D. Inhalation Is Active And Exhalation Is Active

Answer: (B)

Breathing at rest uses muscles to draw air in and relies on elastic recoil to push air out. Inhalation is active because the diaphragm contracts and the external intercostal muscles lift the ribs, expanding the chest cavity. This expansion drops intrapulmonary pressure below atmospheric pressure, so air flows into the lungs. Exhalation during quiet breathing is passive: once the inspiratory muscles relax, the lungs and chest wall recoil, increasing pressure and pushing air out without energy expenditure. Only during heavy or forceful breathing does exhalation require active muscle work (internal intercostals and abdominal muscles). That’s why the statement that inhalation is active and exhalation is passive best fits normal resting breathing.