The System of the Leaf
The complexity of the leaf is all protected by the lower and upper epidermis, a layer of protective cells that help stop the insides from being damaged. These are also covered in a cuticle, which is another thin protective laying, almost like plastic, that helps to keep moisture in and out of the inside of the leaf.
In the lower epidermis, guard cells exist almost as like little pores that help with controlling the gas exchange of the environment and the plant and are found where the stomata is. These cells when dry will close and prevent less and less gas from coming in and leaving. The stomata is the part of the chloroplast (the organelle responsible for photosynthesis) that does 'dark' reactions (or the Calvin cycle). These dark reactions use ATP and NADPH (two forms of energy) to turn Carbon Dioxide into Glucose.
The chloroplasts themselves are held inside the pallisade and spongy layer of the leaf and are considered to both be mesophyll layers, or the layers of where the chloroplasts resides. The pallisade layer is a more concentrated layer in which the chloroplasts exist whereas the spongy layer stores extra gases for photosynthesis. This also exists with air space which is the communication between the outside of the leaf and the inside of the leaf through the air. This helps the leaf react to certain environmental changes to help it survive.
The veins of the leaf have a xylem and phloem tube. The xylem is meant to transport water from the root of the plant all the way through out it's body, while the phloem tube is meant to take the food those chloroplasts have been hard at work making and distributing it around the plant as well.