Expert: Walter Hintz - 3/27/2006

Question
I need help comparing and contrasting the gas exchange systems of birds, fish, and humans.  Why can birds and fish outperform mammals in environments where the concentration of O2 is low?

Answer
Hi Kyle;  First of all keep in mind that fish require less O2 then birds and mammals since they are cold blooded with a slower metabolic rate.  Also the gill is adapted for gas exchange in water and the lung is not.  If a mammal were to submerge and flood the alveoli with water some gases would exchange but the O2 concentration in water is not near the 20% in the air.  I cannot answer your question about birds in low O2 concentrations.  AS far as I know they need as much O2 as mammals if not more.