Final answer:
The elastic fibres in the walls of the alveoli allow them to stretch during inhalation, increasing the surface area for gas exchange. They recoil during exhalation to prevent collapse.
Step-by-step explanation:
The elastic fibres in the walls of the alveoli serve an important function in the lungs. These fibres allow the alveoli to stretch during inhalation, increasing the surface area available for gas exchange. When the alveoli contract during exhalation, the elastic fibres recoil, helping to prevent the collapse of the alveoli.