Final answer:
Surfactant reduces the surface tension of the alveoli, preventing them from collapsing.
Step-by-step explanation:
The surface tension of the alveoli is reduced by surfactant, which is a complex mixture of phospholipids and lipoproteins. This surfactant works to lower the surface tension between the alveoli tissue and the air within the alveoli. By reducing the surface tension, the tendency of alveoli to collapse is decreased.