Photosynthesis is the chemical process by which plants make their own food. It is one of the most important reactions on Earth. The ability of green plants to make their own food (organisms that can generate their own food are called autotrophs; those that cannot make their own food are called heterotrophs) allows heterotrophs to have food by consuming autotrophs. Food is potential chemical energy. As a result, there must be another energy source to make it. Autotrophs use sunlight as their source of energy. The sunlight is absorbed by the green pigments called chlorophll in the chloroplasts in the leaves of plants. The plant uses the sunlight plus water obtained from the soil plus carbon dioxide obtained from the air, to synthesize food (glucose) while oxygen is returned to the air. The chemical equation for photosynthesis is as follows:
Sunlight + 6H2O + 6CO2 ----> C6H12O6 + 6O2 -----(1)
Equation (1) is an expression of Pj problems because it is a chemical reaction (all chemical reactions are expressions of Pj problems).
Pj problems are also expressed implicitly in equation (1): the sunlight (energy), the chlorophyll, reactants and products (molecular bonds and molecular shapes).
Chlorophyll is the main plant pigment involved in photosynthesis. However, other non-green plant pigments such as the orange or yellow carotenoids (e.g carrots), red or yellow betalains, and red, purple, or blue anthocyanins, also carry out photosynthesis.