Light Reaction in Photosynthesis

1. Happens = in photosystem (in thylakoid membrane).
2. Involved only PSI (In cyclic photophosphorylation)
3. Energised e-:
• are released from the excited chlorophyll a (P700)
• is picked up by a primary acceptor.
• pass through electron transport chain
• return to P700
•  by releasing energy (to produce ATP from ADP and Pi).
4. 
   

   

   Cyclic photophosphorylation

   Involved both PSI and PSII (In non-cyclic photophosphorylation)
5. Energised e- :
• are released from the excited chlorophyll a (P680)
• is picked up by the primary acceptor.
• are transported to cytochrome complex
• through the elcetron carrier plastoquinone 
• during which its energy is trapped to form ATP.
6. Electron hole:
• is formed in P680 due to the transport of the excited electron
• is filled up by the electron produced during photolysis.
7. Low energy level e-:
• from the cytochrome complex are transported to P700 through plastocyanin.
• transportedfrom P700 to NADP for reduction (catalyzed by NADP+ reductase (enzyme)
• via the primary acceptor and ferredoxin.
8. Net energy gain (during non-cyclic photophosphorylation) = 1 mol ATP + 1 mol NADPH.

Non-cyclic photophosphorylation