Final answer:
Mammalian lungs are more efficient due to the presence of alveoli and improved countercurrent exchange.
Step-by-step explanation:
Mammalian lungs are more efficient than reptile lungs because they have both alveoli for increased surface area and improved countercurrent exchange. Alveoli are tiny air sacs in the lungs that provide a large surface area for gas exchange. They greatly increase the efficiency of oxygen uptake and carbon dioxide removal. Countercurrent exchange is a mechanism in which blood flows in the opposite direction to air flow, creating a favorable diffusion gradient and maximizing oxygen uptake. This is a more efficient process compared to reptiles, which have less surface area and lack countercurrent exchange.