Photosynthesis is the process by which plants and some protistans use the energy of the Sun to produce sugar, which cellular respiration converts into ATP, the "fuel" used by all living things. The conversion of unusable sunlight is associated with a green pigment called chlorophyll.
Julius Von Sachs(1832-1897) , a German botanist and physiologist initiated experimental plant physiology to study in the effects of light and heat on plants and how plants get their food. In 1854, Sachs showed that plants produce sugar with the help of a green pigment called chlorophyll. Sachs also showed that chlorophyll is not spread throughout the plant, instead it is present only on the leaves. Which is why leaves are green in color.