11.2 E ARLY E XPERIMENTS · Part 3

that would represent the overall process of photosynthesis is therefore: CO H O C H O H O O Light  →  where C H O represents glucose. The O released is from water; this was proved using radio isotope techniques. Note that this is not a single reaction but description of a multistep process called photosynthesis. Can you explain why twelve molecules of water as substrate are used in the equation given above?