Undoubtedly the primary function of photosynthesis is the conversion of light energy to chemical energy. The process is carried out in a specialized organelle called chloroplast. Thylakoid membranes in the chloroplast has pigments called chlorophyll that can trap light energy and ultimately leading to the formation of carbohydrate or food. Degradation of carbohydrate during respiration yields chemical energy called ATP that is utilized for carrying out various cellular activities.
This is the process that is responsible for the phenomenon 'life' on this planet for three reasons
1) During photosynthesis, O2 is evolved and is required for all organism.
2) All organisms are dependent on plants either directly or indirectly for food.
3) Atmospheric CO2, O2 concentration is maintained by plants, increase in CO2 concentrations may lead to global warming.
For more on chloroplast: http://biologyexams4u.blogspot.com/2012/03/chlorop...