Biochemistry of Photosynthesis
Overall Word Equation:
Water+ Carbon Dioxide( Carbohydrates+ Oxygen ((: light + chlorophyll)
1. Light Dependent Stage/ photochemical reaction/ light reactions:
Water ( Hydrogen ions + Oxygen ((: light + chlorophyll)
Site: On the Thylakoid membrane of the chloroplast
• Light absorption
o Chlorophyll in the thylakoids absorbs light. The energy absorbed is used for photolysis (splitting of water molecules).
• Photolysis of water (Photodissociation)
o The light energy absorbed split H2O molecules into H+ ions and O2
▪ 2H2O(4H+ +4e- + O2
▪ O2 is released as a gas to the atmosphere (as a by-product)
▪ H+ ions is accepted by NADP to form NADPH2
• NADPH2 acts as a reducing agent by donating H+ ions in Calvin Cycle.
• Generation of ATP (Adenosine triphosphate)
o The light energy absorbed is used to form ATP (photophosphorylation)
o In this way, light energy is converted to chemical energy stored in ATP
▪ Used to drive the reactions in Calvin Cycle
Products formed in this stage:
• Photolysis of water molecules to give H+ ions and O2
• ATP molecules: as energy source for subsequent synthesis of carbohydrates in light dependent reactions.
The flow of electrons in Photosynthesis
Photosystem: Consists of chlorophyll molecules & accessory pigments e.g. carotenoid accessory pigments trap light energy and pass to the chlorophyll.
Results of chromatography:
2. Light independent stage/ carbon fixation/ dark reactions
Carbon dioxide + Hydrogen ions ( Carbohydrates + Water ((enzymes)
• Site: In the stroma of chloroplast with the presence of enzymes for dark...
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