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

$$6CO_2 + 18ATP + 12NADPH + H^+ \rightarrow 18ADP + 18P_i + 12NADP^+ + \text{glucose}$$

In a nutshell

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