Besides letting gases move about, what else do the air spaces of the spongy mesophyll give a leaf?
A larger external surface area of the leaf blade facing the light
Extra strength, so the leaf can hold itself out flat
A large internal surface area of moist cell walls in contact with air✓Correct answer
A store of water that the leaf can draw on whenever the soil goes dry
Explanation
Every cell bordering a space adds its own damp surface to the area over which gases can pass into and out of the tissue, so the inside of a leaf offers far more exchange surface than its outside does. That internal area is a different quantity from the flat outer area of the blade, which is what catches the light.