Mechanism of Breathing · NCERT Biology

The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration occurs when:

  1. Intra-pulmonary pressure is higher than atmospheric pressure
  2. Intra-pulmonary pressure is lower than atmospheric pressure
  3. Intra-pulmonary pressure is equal to atmospheric pressure
  4. Intra-pleural pressure becomes positive
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Correct answer: Intra-pulmonary pressure is lower than atmospheric pressure

Inspiration is initiated when the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure. This negative pressure gradient draws air from the outside into the alveoli.

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