It's a process of converting light energy to chemical energy and storing it in the bonds of sugar, it occurs in plants. Plants need only light energy, CO2 and H2O to make sugar. The process of photosynthesis takes place in the chloroplast, using chlorophyll, the green pigment involved in photosynthesis.
It takes place in plant leaves and occurs in stems. It includes the upper and lower epidermis, the mesophyll, the vascular bundle(s) (veins) and the stomates.
The upper and lower epidermal cells have no chloroplasts, however photosynthesis does not occur there and they are needed for protection for the rest of the leaf. The stomates are holes which occur primarily in the lower epidermis and are for air exchange: they let CO2 in and O2 out.
The vascular bundles (xylem and phloem) or veins in a leaf are part of the plant's transportation system, moving water and nutrients around the plant as needed. The mesophyll cells have chloroplasts and this is where photosynthesis occurs.
Chlorophyll is green, because it absorbs red and blue light. It is the green light which is not absorbed that reaches our eyes, making it appear green. The green light we can see is not absorbed by the plant and can't be used to do photosynthesis.
The chemical reaction in photosynthesis is:
6CO2 + 6H2O (+ light energy) -> C6H12O6 + 6O2.
There are two parts to photosynthesis:
The light reaction happens in the thylakoid membrane and converts light energy to chemical energy, this must take place in the light. Chlorophyll and other pigments are organized in clusters in the thylakoid membrane and are involved in the light reaction. These
differently-colored pigments can absorb different color of light and pass its energy to the central chlorophyll molecule to do photosynthesis.
You can find other information and more details in this site:
http://biology.clc.uc.edu/courses/bio104/photosyn.htm
