The process of formation of CO2 and O2 during photosynthesis is called the Hill reaction or photolysis of water. This primary photochemical reaction takes place in the presence of sunlight. The reaction is associ­ated with chlorophyll, and after receiving light energy, the chlorophyll becomes activated. The steps in the Hill reaction can be summed up in the following manner:

1. Absorption of light and activation of chlorophyll Radiant light contains very tiny energized particles called photons or quanta, which are absorbed by the chlorophyll and it becomes activated.

2. Photolysis Is the dissociation of water molecules by light energy that have been absorbed by the chlorophyll. The reaction can be rep­resented as

4H2O Llghtenergy> 4H+ + 4OH-

H2 + NADP ^ NADPH2 (Hydrogen acceptor)

3. Photophosphorylation This is the stage of formation of ATP from ADP

ADP + Pi ^ ATP