Light-Independent Reaction

Rucete ✏ Biology In a Nutshell

1. What Is the Light-Independent Reaction?

• Also known as the Calvin Cycle or dark reaction.
• Occurs in the stroma of chloroplasts.
• Uses ATP and NADPH produced from light-dependent reactions to convert CO₂ into glucose.

2. Calvin Cycle Process

• Cycle repeats 6 times to produce one molecule of glucose from 6 molecules of CO₂.

① Carboxylation

• 6 CO₂ molecules combine with 6 RuBP (ribulose bisphosphate).
• Catalyzed by enzyme rubisco.
• Produces 12 PGA (3-carbon phosphoglycerate molecules).

② Reduction

• 12 ATP and 12 NADPH convert 12 PGA into 12 G3P (glyceraldehyde-3-phosphate).

③ Regeneration

• 6 ATP used to convert 10 G3P back into 6 RuBP.
• RuBP regenerated to continue the Calvin cycle.

④ Carbohydrate Synthesis

• Of the 12 G3P molecules:
  • 10 G3P recycled for RuBP regeneration.
  • 2 G3P used to synthesize glucose.

3. Overall Reaction

6CO₂ + 18ATP + 12NADPH + H⁺ → 18ADP + 18Pᵢ + 12NADP⁺ + glucose

In a nutshell

• Although termed a dark reaction, Calvin cycle depends on ATP and NADPH from light-dependent reactions (photophosphorylation).