The epidermis, like our epidermis, is the skin of the leaf. It is transparent and keeps the leaf hydrated, preventing water from leaving the leaf. The stomata, which is a part of the epidermis, allows the leaf to "breathe" by pushing carbon dioxide and oxygen in and out of the leaf. This part of the leaf also allows water vapor to move out of the stomata during a process called "transpiration." This stomata closes up and sleeps at night just like people do!
There are two layers that make up the leaf. They are called the palisade and the spongy layers. In the spongy layers, there are veins that nourish the leaf with food and water. These veins are easily seen when you look at a leaf. The palisade layer is the region where an important process called "photosynthesis." It is made up of many cells that are tightly fitting together.
The cells that are packed together in the palisade layer are called the mesophyll cells. In the spongy layer, these cells aren't as close together as in the palisade and are separated by spaces of air. The mesophyll cells play an important role in the photosynthesis process as they contain the chloroplasts where this photosynthesis occurs.
This part isn't as easy to see as the others. Chloroplasts are tiny cells located inside the mesophyll cells. These chloroplasts are always reproducing themselves inside the mesophyll cells. Chloroplasts are a food factory for the leaf and plant by producing carbohydrates. The engine of this factory is powered by the sun as well as carbon dioxide, water and other minerals.