Calvin cycle involves

Options

A. Oxidative carboxylation
B. Reductive carboxylation
C. Phosphrylation
D. Oxidative phosphorylation.

Answer

**Step-by-Step Solution:**

1. **Understanding the Calvin Cycle**: The Calvin cycle, also known as the C3 cycle, is a crucial process in photosynthesis where carbon dioxide is fixed into organic compounds. It primarily occurs in the stroma of chloroplasts in plants.

2. **Identifying the Key Reactions**: The Calvin cycle consists of a series of reactions that can be categorized into three main phases: carboxylation, reduction, and regeneration of ribulose bisphosphate (RuBP).

3. **Carboxylation Phase**: In the first phase, carbon dioxide is added to ribulose bisphosphate (RuBP) to form an unstable six-carbon intermediate that quickly splits into two molecules of 3-phosphoglycerate (3-PGA), a three-carbon compound. This process is known as carboxylation.

4. **Reduction Phase**: In the second phase, the 3-PGA molecules undergo reduction. This involves the addition of hydrogen (from NADPH) to form glyceraldehyde-3-phosphate (G3P). The addition of hydrogen indicates that this phase is a reduction reaction.

5. **Regeneration Phase**: In the final phase, some of the G3P molecules are used to regenerate RuBP, allowing the cycle to continue. This regeneration is essential for the cycle to repeat.

6. **Conclusion**: Since the Calvin cycle involves both the addition of carbon (carboxylation) and the addition of hydrogen (reduction), it is accurately described as "reductive carboxylation." Therefore, the correct answer to the question is **B: reductive carboxylation**.

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