Mechanism of Breathing · NCERT Biology

During expiration, the air is expelled from the lungs until:

  1. The intra-pulmonary pressure equals the atmospheric pressure
  2. The lungs reach a fully empty state with no residual volume
  3. The diaphragm descends to its lowest anatomical position
  4. The ribs rotate inward and press against adjacent structures
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Correct answer: The intra-pulmonary pressure equals the atmospheric pressure

Air flows out of the lungs as long as the intra-pulmonary pressure is higher than the atmospheric pressure. The flow stops once the two pressures equilibrate.

Difficulty: Medium Question 20 of 20

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