Physicochemical process by which green plants use light energy to synthesize organic compounds. Occurs in Chloroplasts. (Light reactions in grana, Dark reactions in stroma).
Main pigment: Chlorophyll a. Accessory pigments: Chlorophyll b, Xanthophylls, Carotenoids (protect from photo-oxidation).
Involves light absorption, water splitting, oxygen release, and formation of ATP and NADPH.
PS II (P680): Involved in Non-cyclic photophosphorylation. Splitting of water occurs here.
PS I (P700): Involved in both Cyclic and Non-cyclic photophosphorylation.
Chemiosmotic Hypothesis: ATP synthesis is linked to the development of a proton gradient across the thylakoid membrane.
Does not require light directly, but depends on the products of light reaction (ATP, NADPH) to fix CO₂.
C3 Pathway (Calvin Cycle): Primary CO₂ acceptor is RuBP (5C). First stable product is 3-PGA (3C). Key enzyme: RuBisCO.
C4 Pathway (Hatch-Slack): Occurs in plants adapted to dry tropical regions (Maize, Sugarcane). Primary CO₂ acceptor is PEP (3C). First product is OAA (4C). Show Kranz anatomy. Prevents photorespiration.
A wasteful process in C3 plants where RuBisCO acts as an oxygenase (instead of carboxylase) binding to O₂. It releases CO₂ and consumes ATP. No sugar is formed.