Leaves are essential for our world to exist today.  They are how plants survive, and without plants we'd be goners quickly.  It's surprising to me, however, that so few people know what a leaf contains in it.  Below here, I have a basic diagram and a more complex diagram on the inner workings of leaves.  Enjoy! 

Veins: Veins are basically tubes within the leaf that carry water and nutrients throughout it. It's similar in concept to a human's veins coursing blood through our body.

Midrib: This just means "central vein" within the leaf. All the other veins sprout off of it.

Blades: These generally are long, flat, and have a good surface area, to capture the maximum amount of sunlight

Nodes: This is the exact spot where the leaf connects itself ot the stem. It needs to be strong and flexible, since the leaves will undoubtedly sway in the wind.

Petioles: There adjust the leaves as necessary. It allows them to get the maximum power from sunlight during a day, not just during full noon.

This is a far closer picture of a leaf, getting into the cellular functions. For a more full and complete description of cellular functions, please go here.