The methodology, which has been most useful for investigating the Calvin cycle, is

Options

A. Radioactive isotope technique
B. Inverted funnel experiment
C. Half leaf experiment
D. Flash light experimental technique

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Calvin Cycle**: The Calvin cycle is a crucial part of photosynthesis where carbon dioxide is fixed into organic molecules. Investigating this cycle helps us understand how plants convert light energy into chemical energy.

2. **Identifying Methodologies**: There are several methodologies used to study the Calvin cycle. The question asks for the most useful one.

3. **Evaluating Options**:
- **Option 1: Radioactive Isotope Technique**: This method involves using radioactive carbon (specifically carbon-14) to trace the path of carbon during photosynthesis. Calvin used this technique to determine how carbon from CO2 is incorporated into organic compounds like starch and sucrose.
- **Option 2: Inverted Funnel Experiment**: This experiment demonstrates that oxygen is produced during photosynthesis but does not specifically investigate the Calvin cycle.
- **Option 3: Half-leaf Experiment**: Conducted by scientist Moll, this experiment shows that CO2 is necessary for photosynthesis but does not delve into the specifics of the Calvin cycle.
- **Option 4: Flashlight Experimental Technique**: This experiment illustrates phototropism, the growth of plants towards light, and does not relate to the Calvin cycle.

4. **Conclusion**: The most useful methodology for investigating the Calvin cycle is the radioactive isotope technique, as it directly tracks the incorporation of carbon into organic molecules during photosynthesis.

**Final Answer**: The methodology which has been most useful for investigating the Calvin cycle is the **radioactive isotope technique**.

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