Moderate

Lungs are made up of air­filled sacs, the alveoli. They do not collapse even after forceful expiration because of:

Correct answer: D. Residual Volume

  • A. Inspiratory Reserve Volume
  • B. Tidal Volume
  • C. Expiratory Reserve Volume
  • D. Residual Volume

Explanation

Residual volume is the volume of air which remains in the lungs after the most forceful expiration. This residual air enables the lungs to continue the exchange of gases even after maximum exhalation. Due to this, lungs do not collapse even after forceful expiration.

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About Respiration

The human respiratory system includes the air passages, lungs, alveoli and breathing muscles, while gaseous exchange explains how oxygen enters blood and carbon dioxide leaves it by diffusion. The effects of smoking include damage to cilia and alveoli, reduced gas exchange, chronic bronchitis, emphysema and increased risk of lung cancer.

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