What is the function Alveoli?

The main function of the alveoli is storage of air for a shorter period which permits absorption of oxygen into the blood. The gaseous exchange of oxygen and carbon dioxide typically takes place in the alveoli. The main function of the bronchiole is to allow the passage of air freely into the lungs

not: both offer magnification to the atomic level.

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.