In most birds air sacs are ____________ in number?
Correct answer: D. 9
- A. 10
- B. 3
- C. 4
- D. 9
Explanation
Most birds have nine air sacs: cervical, clavicular, anterior thoracic, posterior thoracic and abdominal sacs. These sacs act as bellows and maintain a continuous flow of air through the lungs. The common mistake is choosing 10 by confusing the number of air sacs with the number of lungs or air passages.
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About Human Respiratory System
The human respiratory system conducts air to the alveoli, where oxygen and carbon dioxide exchange occurs across thin respiratory surfaces. Questions cover the nasal passage, trachea, bronchi, lungs, diaphragm and intercostal muscles, ventilation mechanics and gas transport, while distinguishing breathing and gaseous exchange from cellular respiration.
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