Growth promoting hormone is

Options

A. 2, 4-D
B. ABA
C. Gibberellin
D. IAA.

Answer

**Step-by-Step Solution:**

1. **Understanding Plant Hormones**:
- Plant hormones, also known as phytohormones, are substances that regulate various physiological processes in plants, including growth, development, and responses to environmental stimuli.

2. **Classification of Plant Hormones**:
- Plant hormones can be classified into two main categories:
- **Growth Promoting Hormones**: These hormones stimulate growth activities.
- **Inhibitory Hormones**: These hormones inhibit growth and other activities.

3. **Identifying Growth Promoting Hormones**:
- The main growth promoting hormones include:
- **Auxins**: Promote cell elongation and growth.
- **Cytokinins**: Promote cell division and shoot formation.
- **Gibberellins**: Promote stem elongation and seed germination.
- **Ethylene**: Can act as both a promoter and inhibitor depending on the context.

4. **Identifying Inhibitory Hormones**:
- The primary inhibitory hormone is **Abscisic Acid (ABA)**, which inhibits growth and promotes stress responses.

5. **Specific Examples**:
- **2,4-Dichlorophenoxyacetic acid (2,4-D)**: This is a synthetic auxin that is used for specific applications like inducing flowering and preventing pre-harvest fruit drop, but it is not classified as a growth promoting hormone.
- **Indole Acetic Acid (IAA)**: This is a natural auxin, but it is not the primary growth promoting hormone in this context.

6. **Conclusion**:
- Among the hormones discussed, **Gibberellins** are recognized as the primary growth promoting hormone due to their significant role in promoting growth, particularly in stem elongation.

7. **Final Answer**:
- The growth promoting hormone is **Gibberellin**.

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