Question

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?

O They must not belong to the respiratory system.
O They cannot effectively moisturize the air before it reaches the lungs.
O They are not efficient sites of gas exchange between air and blood.
O They cannot be derived from endoderm.

Answer 1

Birds' air sacs, which are neither thin nor highly vascularized, are not the primary sites for gas exchange; this function mainly occurs in air capillaries within the lungs through a counter-current exchange system.

Step-by-step explanation:

The observation that air sacs in birds are neither thin nor highly vascularized indicates that they are not efficient sites of gas exchange between air and blood. The primary function of the birds respiratory system, particularly the air sacs, is to provide unidirectional airflow through the lungs while gas exchange occurs in specialized structures called air capillaries located within the lungs by a counter-current exchange mechanism. The air sacs are an integral part of the flow-through respiratory system contributing to the bird's lighter body mass and aiding in its higher metabolic demands during flight. Therefore, the correct inference about the air sacs given the observation is that they are not efficient sites of gas exchange between air and blood, not that they do not belong to the respiratory system, cannot effectively moisturize the air, or are not derived from endoderm.