Question:
Number of ATP and NADP required for every CO2 molecule entering the Calvin cycle.
Number of ATP and NADP required for every CO2 molecule entering the Calvin cycle.
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To synthesize 1 molecule of glucose (\(6 \text{ CO}_2\)), the cycle must turn 6 times.
Total requirements = \( 6 \times 3 \text{ ATP} = 18 \text{ ATP} \) and \( 6 \times 2 \text{ NADPH} = 12 \text{ NADPH} \).
Total requirements = \( 6 \times 3 \text{ ATP} = 18 \text{ ATP} \) and \( 6 \times 2 \text{ NADPH} = 12 \text{ NADPH} \).
Updated On: Jul 22, 2026
- 3 ATP 3 NADP
- 2 ATP 2 NADP
- 18 ATP 12 NADP
- 3 ATP 2 NADP
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question:
The question asks for the specific quantity of ATP and NADPH (referred to as NADP in the question) required to fix one molecule of carbon dioxide (\(\text{CO}_2\)) during the dark reactions (Calvin cycle) of photosynthesis.
Step 2: Key Formula or Approach:
The Calvin cycle has three main phases: Carboxylation, Reduction, and Regeneration.
We calculate the energy input at each phase per molecule of \(\text{CO}_2\) fixed.
Step 3: Detailed Explanation:
• Carboxylation: \(\text{CO}_2\) combines with Ribulose-1,5-bisphosphate (RuBP) to form two molecules of 3-phosphoglyceric acid (3-PGA). This step does not consume ATP or NADPH.
• Reduction: Two molecules of 3-PGA are converted to two molecules of glyceraldehyde-3-phosphate (G3P).
This step requires 2 ATP and 2 NADPH molecules per \(\text{CO}_2\) fixed.
• Regeneration: Regeneration of the \(\text{CO}_2\) acceptor molecule (RuBP) requires phosphorylation, which consumes 1 ATP molecule.
• Total Energy Consumption: Summing up the energy requirements per single turn of the cycle (\(1 \text{ CO}_2\)): \[ \text{ATP required} = 2 \text{ (Reduction)} + 1 \text{ (Regeneration)} = 3 \text{ ATP} \] \[ \text{NADPH required} = 2 \text{ (Reduction)} = 2 \text{ NADPH} \]
Step 4: Final Answer:
Fixing one molecule of \(\text{CO}_2\) in the Calvin cycle requires 3 ATP and 2 NADPH.
The question asks for the specific quantity of ATP and NADPH (referred to as NADP in the question) required to fix one molecule of carbon dioxide (\(\text{CO}_2\)) during the dark reactions (Calvin cycle) of photosynthesis.
Step 2: Key Formula or Approach:
The Calvin cycle has three main phases: Carboxylation, Reduction, and Regeneration.
We calculate the energy input at each phase per molecule of \(\text{CO}_2\) fixed.
Step 3: Detailed Explanation:
• Carboxylation: \(\text{CO}_2\) combines with Ribulose-1,5-bisphosphate (RuBP) to form two molecules of 3-phosphoglyceric acid (3-PGA). This step does not consume ATP or NADPH.
• Reduction: Two molecules of 3-PGA are converted to two molecules of glyceraldehyde-3-phosphate (G3P).
This step requires 2 ATP and 2 NADPH molecules per \(\text{CO}_2\) fixed.
• Regeneration: Regeneration of the \(\text{CO}_2\) acceptor molecule (RuBP) requires phosphorylation, which consumes 1 ATP molecule.
• Total Energy Consumption: Summing up the energy requirements per single turn of the cycle (\(1 \text{ CO}_2\)): \[ \text{ATP required} = 2 \text{ (Reduction)} + 1 \text{ (Regeneration)} = 3 \text{ ATP} \] \[ \text{NADPH required} = 2 \text{ (Reduction)} = 2 \text{ NADPH} \]
Step 4: Final Answer:
Fixing one molecule of \(\text{CO}_2\) in the Calvin cycle requires 3 ATP and 2 NADPH.
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