To sustain the extremely high metabolic rate required for homoiothermy and powered flight, birds (Aves) possess a respiratory system that functions differently from that of mammals (Mammalia). Which of the following structural arrangements enables continuous, unidirectional airflow across the parabronchi during both inhalation and exhalation in birds?
- A system of posterior and anterior air sacs acting as bellows to move air unidirectionally through the lungsAnswer
- BContraction and relaxation of a muscular diaphragm to alter thoracic cavity volume during tidal ventilation
- CBlind-ending alveolar sacs that trap incoming air for gas exchange before expelling it out the same pathway
- DIncomplete ventricular septum in a three-chambered heart that recirculates partially oxygenated air to the lungs
Answer
A system of posterior and anterior air sacs acting as bellows to move air unidirectionally through the lungs
The correct option describes the unique avian respiratory adaptation where non-gas-exchange air sacs (posterior and anterior) function as bellows. This setup directs air in a single direction across the parabronchi of the lungs during both inspiration and expiration, ensuring continuous oxygenation without mixing fresh and stale air.
Step-by-Step Solution
Key Concept
Avian Air Sac System and Unidirectional Lung Ventilation