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Breathing and Exchange of Gases — BIOLOGY STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYBreathing and Exchange of Gases3 Marks
Question
How is expiration carried out under normal physiological conditions?
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Answer

  1. Expiration occurs when the intra-pulmonary pressure is greater than the atmospheric pressure.
  2. The diaphragm muscles and the intercostal muscles relax.
  3. The diaphragm moves upward and the rib cage downward and inward.
  4. This causes a decrease in the volume of the thoracic cavity, that results in an increased intra-pulmonary pressure.
  5. So air rushes out of the lungs (expiration) into the atmosphere.

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