Which of the following elements is most mobile in plant metabolism?

Options

A. Calcium
B. Phosphorus
C. Carbon
D. Magnesium

Answer

To determine which element is the most mobile in plant metabolism, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding Mobility in Plant Metabolism**:
- Mobility refers to the ability of an element to move from one part of the plant to another. In plant metabolism, this is crucial for the distribution of nutrients and other essential compounds.

2. **Evaluating Calcium**:
- Calcium is essential for structural roles in cell walls and membranes. It acts as a counter cation for anions in vacuoles and serves as an intracellular messenger.
- **Conclusion**: Calcium is not mobile as it primarily functions within specific cells and does not move freely throughout the plant.

3. **Evaluating Phosphorus**:
- Phosphorus is involved in nucleic acids and participates in reversible phosphorylation reactions, particularly in the formation of ATP.
- While phosphorus can be considered somewhat mobile, it is noted that it is immobile when present in nucleic acids.
- **Conclusion**: Phosphorus is relatively mobile compared to other elements, making it a potential candidate.

4. **Evaluating Carbon**:
- Carbon forms the basic framework of the plant body through covalent bonds in biomolecules. It is tightly bound and does not move freely within the plant.
- **Conclusion**: Carbon is not mobile in plant metabolism.

5. **Evaluating Magnesium**:
- Magnesium is the central component of chlorophyll and is essential for activating certain enzyme systems. However, it is fixed in the chlorophyll structure.
- **Conclusion**: Magnesium is also not mobile as it is primarily involved in specific structures.

6. **Final Conclusion**:
- After evaluating all the options, phosphorus emerges as the most mobile element in plant metabolism, despite its limitations when bound in nucleic acids.

### Final Answer:
The element that is most mobile in plant metabolism is **Phosphorus**.

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