Zinc is essential for :

Options

A. Biosynthesis of chlorophylls
B. Biosynthesis of 3-IAA
C. Stomatal closing
D. Oxidation of carbohydrates

Answer

To solve the question "Zinc is essential for:", we will analyze the roles of zinc in plant biology and determine which of the provided options is correct.

### Step-by-Step Solution:

1. **Understanding Zinc's Role in Plants**:
- Zinc is classified as a micronutrient, meaning it is required in small amounts by plants.
- It plays a crucial role in various biochemical processes, including enzyme activation and hormone synthesis.

2. **Zinc and Enzyme Activation**:
- Zinc acts as an activator for several enzymes, particularly carboxylases, which are important in various metabolic pathways.

3. **Zinc in Auxin Synthesis**:
- Zinc is essential for the biosynthesis of Indole-3-Acetic Acid (IAA), which is a type of auxin.
- Auxins are plant hormones that regulate various growth processes, including apical dominance.

4. **Evaluating the Options**:
- **Biosynthesis of Chlorophylls**: While zinc is important for plant health, it is not directly involved in chlorophyll synthesis.
- **Biosynthesis of 3IAA**: This is correct as zinc is needed for the synthesis of auxins, including IAA.
- **Stomatal Closing**: This process is primarily regulated by abscisic acid (ABA), not zinc.
- **Oxidation of Carbohydrates**: Zinc does not play a direct role in carbohydrate oxidation.

5. **Conclusion**:
- Based on the analysis, the correct answer is that zinc is essential for the **biosynthesis of 3IAA (Indole-3-Acetic Acid)**.

### Final Answer:
Zinc is essential for the biosynthesis of 3IAA (Indole-3-Acetic Acid).