Final answer:
The tiny air sacs in the lungs where gas exchange occurs are called alveoli.
Step-by-step explanation:
The tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place are called alveoli. These are clusters of many individual alveoli that are responsible for gas exchange. Each alveolus is approximately 200 μm in diameter with elastic walls that allow it to stretch during air intake, increasing the surface area available for gas exchange. Alveoli are connected to their neighbors by alveolar pores, which help maintain equal air pressure throughout the lungs.