Why do bronchiole have a large suface area?

Answer 1

The same concept as why sand is a good absorbent of spilled engine oil, but rocks are not so good.

Assume the bag of fine sand and the bag of large rocks of the same material have the same volume, as indicated by their weights. Although the volumes are the same, the surface areas are much larger in fine sand in large rocks. The large surface area of fine sand can absorb/store much more split engine oil than large rocks can provide.

The lungs work the same way. A large surface area is more efficient in doing its work -- exchanging oxygen and CO2. How to obtain a large surface area? Make a large tube and place little branches on it; the little branches, in turn, would be the platform for even smaller tubing, and so on (like the twigs are growing on branches, which are growing on the tree trunk.)