State that cyclic photophosphorylation and non-cyclic photophosphorylation occur during the light-dependent stage of photosynthesis

Sourav PanOctober 31, 2024

Answered

Photophosphorylation in the Light-Dependent Stage of Photosynthesis

During the Light-Dependent Stage of photosynthesis, light energy is converted into chemical energy in the form of ATP and NADPH. Two types of photophosphorylation processes occur in this stage:

1. Cyclic Photophosphorylation (Cyclic Electron Flow):
   • Location: Thylakoid membranes of chloroplasts
   • Electron Flow:
     • Light energy excites electrons in Photosystem I (PSI)
     • Electrons cycle back to PSI, generating a proton gradient
   • ATP Synthesis:
     • Proton gradient drives ATP synthase to produce ATP from ADP + Pi
   • No Net Change in Electron Acceptors: No NADPH or O2 produced; only ATP generated
2. Non-Cyclic Photophosphorylation (Non-Cyclic Electron Flow):
   • Location: Thylakoid membranes of chloroplasts
   • Electron Flow:
     • Light energy excites electrons in Photosystem II (PSII)
     • Electrons transferred to PSI, then to NADP+, reducing it to NADPH
     • Water (H2O) oxidized, releasing O2
   • ATP and NADPH Synthesis:
     • Proton gradient drives ATP synthase to produce ATP from ADP + Pi
     • Reduced NADPH produced, accepting electrons from the electron transport chain

Key Differences:

Light-Dependent Stage Overview:

• Both cyclic and non-cyclic photophosphorylation occur simultaneously in the thylakoid membranes.
• The ATP and NADPH produced in these processes are utilized in the Light-Independent Stage (Calvin Cycle) to synthesize glucose from CO2.