Micronutrients are needed in very small amount because

Options

A. most of them are mobile in the plant
B. most function as cofactors in enzymes
C. most are supplied in large enough quantities in soil
D. they play only a minor role in the health of the plant

Answer

**Step-by-Step Solution:**

1. **Understanding Micronutrients:**
- Micronutrients are essential elements that plants require in very small quantities. They include elements like iron, manganese, zinc, copper, molybdenum, and boron.

2. **Role of Micronutrients:**
- Despite being needed in small amounts, micronutrients play crucial roles in various physiological processes in plants. They are vital for growth, development, and overall health.

3. **Cofactors in Enzymatic Reactions:**
- One of the primary functions of many micronutrients is to act as cofactors for enzymes. Enzymes are proteins that catalyze biochemical reactions, and cofactors are non-protein molecules that assist in enzyme activity.

4. **Example of Micronutrient as Cofactor:**
- For instance, molybdenum is a micronutrient that serves as a cofactor for the enzyme nitrogenase, which is essential for nitrogen fixation in plants.

5. **Evaluating Other Options:**
- Option 1: "Most of them are mobile in the plant" - This is incorrect because mobility is more characteristic of macronutrients like nitrogen and phosphorus.
- Option 2: "Most are supplied in large enough quantities in soil" - This is incorrect as the most abundant nutrients in soil are macronutrients, not micronutrients.
- Option 3: "They play only a minor role in the health of the plant" - This is also incorrect because, although they are needed in small amounts, micronutrients have a significant impact on plant health and development.

6. **Conclusion:**
- Therefore, the correct answer to the question is that micronutrients are needed in very small amounts because most function as cofactors in enzymes.