photosynthesis

Conversion of light energy into chemical energy, storing solar power in the bonds of glucose. The process that feeds nearly all life on Earth.

reaction

6CO2 + 6H2O + light energy → C6H12O6 + 6O2

stages

light-dependent reactions (thylakoid membranes)

• photosystem II absorbs light, splits water (photolysis), releases O2
• electron transport chain generates a proton gradient
• photosystem I re-energizes electrons
• ATP synthase produces ATP; NADP+ is reduced to NADPH

light-independent reactions (Calvin cycle, stroma)

• carbon fixation: RuBisCO enzyme fixes CO2 into 3-phosphoglycerate
• reduction: ATP and NADPH convert intermediates to glyceraldehyde-3-phosphate (G3P)
• regeneration: RuBP is regenerated to continue the cycle

pigments

Chlorophyll a and b absorb red and blue light, reflect green. Carotenoids absorb blue-green, serve as accessory pigments and photoprotection.

connections

The reverse of oxidation in cellular respiration — photosynthesis reduces CO2 while respiration oxidizes glucose. Products feed fermentation and combustion. polymerization of glucose yields cellulose and starch. The process embodies joy — turning light into life.