Which hormone is responsible for apical growth
(a) IAA
(b) ABA
(c) GA
(d) All of these

Options

A. IAA
B. ABA
C. GA
D. All of these

Answer

To determine which hormone is responsible for apical growth, we need to analyze the options provided:

1. **Understanding Apical Growth**:
- Apical growth refers to the growth that occurs at the tips of the plant, specifically in the apical meristems. This type of growth is crucial for the elongation of stems and roots.

2. **Analyzing the Hormones**:
- **(a) IAA (Indole Acetic Acid)**:
- IAA is a type of auxin, which is known to promote apical growth. It stimulates cell elongation and is involved in the phenomenon of apical dominance, where the growth of lateral buds is inhibited.
- **(b) ABA (Abscisic Acid)**:
- ABA is primarily a stress hormone. It is involved in processes such as senescence (aging of plant tissues) and abscission (the shedding of leaves or fruits). It does not promote apical growth.
- **(c) GA (Gibberellic Acid)**:
- GA is associated with stem elongation and seed germination. While it does promote growth, it is not specifically responsible for apical growth like auxins are.
- **(d) All of these**:
- This option suggests that all the hormones listed contribute to apical growth, which is incorrect based on the specific roles of each hormone.

3. **Conclusion**:
- Based on the analysis, the hormone responsible for apical growth is **IAA (Indole Acetic Acid)**. Therefore, the correct answer is **(a) IAA**.

### Step-by-Step Solution:
1. Define apical growth and its significance in plants.
2. Identify and analyze each hormone's role in plant growth:
- IAA: Promotes apical growth and apical dominance.
- ABA: Involved in stress responses, not apical growth.
- GA: Associated with stem elongation and seed germination, but not specifically apical growth.
3. Determine that only IAA is responsible for apical growth.
4. Conclude that the correct answer is **(a) IAA**.