Topics:
Animal Physiology, Animal Refresher
Basic Unit of Gaseous Exchange in Birds
The basic unit of gaseous exchange in birds is:
- Parabronchi — Correct Answer
- Lungs
- Air sacs
- Alveoli
Explanation:
Correct Answer: Parabronchi
In birds, the basic functional unit of gaseous exchange is the parabronchi (tertiary bronchi), not alveoli as in mammals. Parabronchi are tiny tubes through which air flows past capillaries in a cross-current or counter-current manner, making avian gas exchange more efficient than mammalian gas exchange.
Avian vs. Mammalian Respiratory System
| Feature | Birds | Mammals |
|---|---|---|
| Gaseous exchange unit | Parabronchi | Alveoli |
| Diaphragm | Absent | Present |
| Air sacs | 9 air sacs (avascular, no exchange) | Absent |
| Expiration | Active process | Passive process |
| Surfactant-secreting cells | Granular cells | Type-II pneumocytes |
Types of Parabronchi
- Paleopulmonic parabronchi: Present in ALL birds; air flow is UNIDIRECTIONAL.
- Neopulmonic parabronchi: Absent in penguin & emu; air flow is BIDIRECTIONAL; more developed in fowl and songbirds.
Why Other Options Are Wrong
- Air sacs → Avascular structures that serve as bellows to move air through the lungs; NO gaseous exchange occurs in air sacs.
- Alveoli → The mammalian unit; birds do not have alveoli.
- Lungs → An organ, not the unit of exchange.
📚 About this Topic — Animal Physiology
This multiple choice question is from Animal Physiology, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Physiology to strengthen your preparation.
