Inhaling and exhaling result mainly from contractions of the

• A. Brain
• B. Lungs
• C. Diaphragm
• D. Heart

Answer: (C)

Breathing is driven by the diaphragm, a large muscle located just below the lungs. When the diaphragm contracts, it moves downward and flattens, expanding the chest cavity and increasing its vertical dimension. This makes the air pressure inside the lungs drop below the outside air pressure, so air rushes in—that’s inhalation. When the diaphragm relaxes, it returns to its dome shape, reducing the chest volume and increasing internal pressure, which pushes air out—that’s exhalation. At rest, breathing is mostly a passive process due to the lungs and chest walls’ elasticity, with the diaphragm doing the primary work; during harder breathing, other muscles help as well. The brain regulates how fast and deep we breathe, but it doesn’t physically move the air; the lungs are where air goes, and the heart pumps blood, not air.