The lungs are very efficent at gas exchange because they have a:

Question

High mass

Low volume

High surface area-to-volume ratio

Low surface area-to-volume ratio

Answer 1

High surface area-to-volume ratio

Answer 2

Very efficient at gas exchange because of a high surface area-to-volume ratio as a result of the many branching bronchial tubes and multiple tiny aveioli (sacs).  

With such efficient gas exchangers, it's a shame our ability to breath is so inefficient.  We rarely use more than the top third of our lung capacity, almost never fully utilizing the lower portion of our lungs.

Birds, however, make use of their entire lung system with a continuous flow all the way to the back of their lungs and then forward when they exhale.  They also have the efficient gas exchangers, aveioli that provides a high surface-area to volume ratio.

Answer 3

high surface are to volume ratio. means more can be absorbed in less space, which  is good.

make it a good day.