Which of the following is essentially regenerated to complete the Calvin cycle

Options

A. PGA
B. RUBP
C. PEP
D. OAA

Answer

To solve the question, "Which of the following is essentially regenerated to complete the Calvin cycle?" we will analyze the options provided and understand the Calvin cycle's process.

### Step-by-Step Solution:

1. **Understanding the Calvin Cycle**: The Calvin cycle, also known as the light-independent reactions or the dark reactions, is a crucial part of photosynthesis where carbon dioxide is fixed into organic molecules. It consists of three main phases: carbon fixation, reduction, and regeneration.

2. **Identifying the Options**:
- **PGA (3-phosphoglyceric acid)**: This is an intermediate formed during the Calvin cycle but is not regenerated.
- **RUBP (ribulose 1,5-bisphosphate)**: This molecule is essential for the Calvin cycle as it is regenerated at the end of the cycle.
- **PEP (phosphoenolpyruvate)**: This is involved in the C4 pathway and is not part of the Calvin cycle.
- **OAA (oxaloacetic acid)**: This is an intermediate in the Krebs cycle and is not involved in the Calvin cycle.

3. **Focusing on RUBP**: The regeneration of ribulose 1,5-bisphosphate (RUBP) is a critical step in the Calvin cycle. After carbon fixation and reduction, RUBP must be regenerated to allow the cycle to continue.

4. **Conclusion**: Among the options provided, RUBP is the molecule that is essentially regenerated to complete the Calvin cycle.

### Final Answer:
**RUBP (ribulose 1,5-bisphosphate)** is the molecule that is essentially regenerated to complete the Calvin cycle.

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