Explain that energy transferred as ATP and reduced NADP from the light-dependent stage is used during the lightindependent stage (Calvin cycle) of photosynthesis to produce complex organic molecules

SouravOctober 31, 2024

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Energy Transfer from Light-Dependent to Light-Independent Stage of Photosynthesis

During photosynthesis, energy is harnessed in two stages: the Light-Dependent Stage (Light Reactions) and the Light-Independent Stage (Calvin Cycle).

Light-Dependent Stage (Light Reactions):

• Occurs in the thylakoid membranes of chloroplasts
• Energy Input: Light (sunlight)
• Energy Conversion:
  • ATP Synthesis: Light energy → ATP (via photophosphorylation)
  • Reduced NADP+ (NADPH) Synthesis: Light energy → NADPH

Light-Independent Stage (Calvin Cycle):

• Occurs in the stroma of chloroplasts
• Energy Input: ATP and NADPH from the Light-Dependent Stage
• Energy Utilization:
  • ATP: Provides energy for CO2 fixation and reduction
  • NADPH: Reduces CO2 into organic forms, ultimately producing glucose (C6H12O6)

Energy Transfer and Utilization in the Calvin Cycle:

1. Carbon Fixation: CO2 is fixed into a 3-carbon molecule (3-phosphoglycerate) via the enzyme RuBisCO, energized by ATP.
2. Reduction: The 3-carbon molecules are reduced to form glyceraldehyde 3-phosphate (G3P) using energy from NADPH.
3. Regeneration: The Calvin Cycle’s intermediate, RuBP, is regenerated using energy from ATP.

Energy Quantities:

• 6 CO2 molecules fixed require:
  • 12 ATP molecules (2 ATP per CO2 fixed in the reduction and regeneration phases)
  • 12 NADPH molecules (2 NADPH per CO2 reduced in the reduction phase)

Outcome:
The energy transferred as ATP and reduced NADP from the Light-Dependent Stage is crucial for the Light-Independent Stage (Calvin Cycle), enabling the production of complex organic molecules, such as glucose (C6H12O6), from CO2 and H2O. This process is essential for the energy and organic compounds needed by the plant and, ultimately, the entire food chain.