The plant leaf, how can this organ be exploited for use by humans?

Question

It sounds really simple, but i cant think of anything other than "food"....help please

Answer 1

Some plant leaves can be dried and smoked.  Some can be ground and used in medicines.

Some can be used as food flavorings.  Large leafed plants are used as protection from the weather by natives.  The leaves of certain plants are used as poisons on their arrows by South American and other natives, to kill animals for food.

Answer 2

Well, the leaf is an incredible structure.  If we can utilise the properties of photosynthesis, we could take very common substances and transcribe the sun's energy efficiently - possibly more so than photovolatic cells.