The respiratory system of birds is one of the most effective respiratory systems of all air-breathing organisms, due to its system of air sacs connected to the lungs. Which of the following can be inferred about the air sacs given the observation that they are neither thin nor highly vascularized?
A) They must not belong to the respiratory system.
B) They cannot be derived from endoderm.
C) They are not efficient sites of gas exchange between air and blood.
D) They cannot effectively moisturize the air before it reaches the lungs.

Question

Quizplus · Accepted Answer

Air sacs in birds, being neither thin nor highly vascularized, are not the primary sites of gas exchange. This is because efficient gas exchange requires a thin barrier between air and blood to allow for easy diffusion of gases, and a high degree of vascularization to transport gases to and from the bloodstream.

The Respiratory System of Birds Is One of the Most