Photosynthesis

Photosynthesis is the synthesis of organic molecules (depicted by glucose) from precursor molecules water and carbon dioxide by the addition of energy from light photons. Photosynthesis is a complex process involving numerous stages mediated by enzymes that capture photons and transfer the energy to chemical bonds. The energy transfer process, an “electron transport chain”, gradually apportions the photons energy to several energy-storing molecules before the final electron acceptor which is water (from which oxygen subsequently is formed).

The primary enzymes of photosynthesis are chlorophyll a, with peak absorption around 415 nm and a lesser peak around 660 nm, and chlorophyll b - an “accessory pigment” with peak absorption around 450 nm and a lesser peak around 640 nm - these are the main green-plant chlorophylls. Chlorophyll c is common in marine algae, also has peak absorption near 450 nm; and chlorophyll d - in cyanobacteria, has peak absorption near 700 nm. Other photosynthesis enzymes are various carotenoids and phycobilins (in cyanobacteria and red algae). “Grow Lights” often have a blue component in the 400-500 nm range, and a red component in the 600 - 700 nm range, giving them a purple appearance.

The energy stored from the electron transport change as an electron loses the energy from a photon, is referred to as the “light reactions”. The stored energy is used to convert carbon dioxide and water into carbohydrates in the “dark reactions”, which do not involve energy transfer from photon-capture directly, but are driven by the energy-storing molecules that were made by the light reactions.