`C_(3)` cycle (reductive pentose phosphate cycle) is basically a

Options

A. `CO_(2)` reduction cycle
B. `CO_(2)` oxdising cycle
C. photochemical reaction
D. Both (2) & (3)

Answer

### Step-by-Step Solution:

1. **Understanding the C3 Cycle**: The C3 cycle, also known as the Calvin cycle or the reductive pentose phosphate cycle, is a crucial process in photosynthesis that occurs in the chloroplasts of plant cells.

2. **Identifying the Nature of the Cycle**: The cycle primarily involves the fixation of carbon dioxide (CO2) from the atmosphere. This means that it takes CO2 and incorporates it into organic molecules.

3. **Reduction Process**: During the cycle, the fixed carbon dioxide undergoes a series of redox (reduction-oxidation) reactions. Specifically, CO2 is reduced to form glucose, which is a carbohydrate that plants use for energy and growth.

4. **Key Enzyme Involved**: The main enzyme that facilitates this process is called Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase). This enzyme plays a critical role in the initial step of the cycle, where it catalyzes the reaction between CO2 and ribulose bisphosphate (RuBP).

5. **Conclusion**: Given that the C3 cycle is fundamentally about the reduction of carbon dioxide to form glucose, we can conclude that it is primarily a carbon dioxide reduction cycle.

### Final Answer:
The C3 cycle (reductive pentose phosphate cycle) is basically a **carbon dioxide reduction cycle**.

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