Which of the following is not a role or function of magnesium

Options

A. It is used in the synthesis of cell wall, particularly as calcium pectate in the middle lamella.
B. It activates enzymes in respiration and photosynthesis, and in the synthesis of DNA and RNA.
C. It is a constituent of the ring structure of chlorophyll and maintains ribosome structure.
D. Deficiency of magnesium induces chlorosis between the leaf veins (interveinal chlorosis) and necrotic or purple coloured spots on older leaves.

Explanation

To determine which of the following is not a role or function of magnesium, we can analyze the functions of magnesium in plants step by step.

### Step-by-Step Solution:

1. **Identify the Nutrient**: The nutrient in question is magnesium, which is classified as a macronutrient. This means that plants require it in relatively large amounts.

2. **Functions of Magnesium**:
- **Enzyme Activation**: Magnesium acts as an activator for various enzymes, particularly those involved in respiration and photosynthesis. This is a key role of magnesium.
- **Chlorophyll Component**: Magnesium is an essential part of the chlorophyll molecule, which is crucial for photosynthesis. This indicates its importance in plant energy production.
- **Ribosome Structure**: Magnesium helps maintain the structure of ribosomes, which are essential for protein synthesis in plants.
- **DNA and RNA Synthesis**: Magnesium is involved in the synthesis of nucleic acids, including DNA and RNA, which are vital for cell division and growth.

3. **Evaluate the Options**: Now, we need to evaluate the provided options to identify which one does not relate to magnesium:
- **Option 1**: "Used in the synthesis of cell wall particularly as calcium pectate in the middle lamella." This function is primarily associated with calcium, not magnesium.
- **Option 2**: "Activates enzymes used in photosynthesis and respiration." This is a correct function of magnesium.
- **Option 3**: "Maintains the structure of ribosomes." This is also a correct function of magnesium.
- **Option 4**: "Causes necrotic and purple colored spots on leaves when deficient." This is a symptom of magnesium deficiency.

4. **Conclusion**: The option that does not represent a function of magnesium is **Option 1**, as it pertains to calcium's role in cell wall synthesis.

### Final Answer:
The correct answer is **Option 1**: "Used in the synthesis of cell wall particularly as calcium pectate in the middle lamella."