Most people understand that the process of photosynthesis takes place in the leaves of plants. However, a plant actually uses a number of specialized structures that conduct the chemical reactions necessary to transform energy from sunlight into energy molecules that the plant can use. In addition to sunlight, plants also require carbon dioxide to perform the initial reactions, which they absorb through tiny pores over their leaves and stems.
The most important part of photosynthesis occurs in the chloroplasts. These small photosynthesis factories buried within the leaves house chlorophyll, a green pigment secreted in the chloroplast membranes. Chlorophyll absorbs a wide range of the spectrum of sunlight, giving the plant as much energy as it can for its reactions. The primary section of the light spectrum that chlorophyll doesn't absorb is green, which explains why leaves usually appear to be some shade of green. These green chloroplasts reside on the leaf's interior. The surface of the leaf that can be touched is actually the epidermis, which protects the processes occurring beneath.
Chloroplasts comprise a number of disks called thylakoids, which are stacked on top of each other to form structures known as grana. Here's where chlorophyll is manufactured, and where sunlight is turned into chemical energy used for later processes. This process occurs almost exclusively in the leaves; very few plants produce chlorophyll anywhere but their leaves.
The second phase of photosynthesis is known as the dark reaction because it doesn't require sunlight to work. The dark reaction takes the atoms of the chemical energy created in the thylakoids and changes them into simple sugars that can be used or stored by the plant, depending on its energy needs. This reaction takes place in another section of the chloroplast called the stroma. Rarely, certain plants, especially those that live in the desert, store carbon dioxide or other necessary components of photosynthesis in other compartments within the plant structure. This allows them to perform the different steps of photosynthesis even when they cannot open up pores to absorb elements from the air or receive energy from the sunlight.