Above you can see what leaves are actually made up of.  This is called a chloroplast.  There are originally believed to have been independant organisms, but over the course of time merged with plants in a beneficial relationship. Inside of the chloroplast you have what look like stacks of pancakes.  These are called granum.  Each pancake is called a thylakoid.  This is where the action happens. The thylakoid is fantastic to study because we can understand how the light from the sun actually benefits the plant itself.  And as you can see from the picture above, the chloroplast is made up stacks of 5-100 thylakoids, with multiple stacks per chloroplast!  This allows the plant to absorb large amounts of energy.