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Air enters the lungs when the pressure inside the lungs is:
AEqual to outside
BFixed at zero
CLower than outside
DHigher than outside
Answer & Solution
Correct answer: C. Lower than outside
1. Air moves down a pressure gradient.
2. For air to flow in, the lungs must be at lower pressure.
3. So intra-pulmonary pressure is below atmospheric.
_Source: NCERT Class 11 Biology, Chapter 17, Breathing and Exchange of Gases._
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