Explanation:
Tiny air sacs at the end of the bronchioles (tiny branches of air tubes in the lungs). The alveoli are where the lungs and the blood exchange oxygen and carbon dioxide during the process of breathing in and breathing out.
At the end of each bronchiole are tiny air sacs called alveoli. This is the place where the exchange of oxygen and carbon dioxide actually happens. Each person has hundreds of millions of alveoli in their lungs.