Which ones regulate stomatal movements (a) IAA (b) `GA_ (c) Zeatin (D) ABA

Options

A. a,c
B. b,c
C. c,d
D. b,d

Answer

To determine which hormone regulates stomatal movements, we need to analyze the options provided: IAA, GA, Zeatin, and ABA.

### Step-by-Step Solution:

1. **Understanding Stomatal Movements**:
- Stomata are tiny openings on the surfaces of leaves that allow for gas exchange. Their opening and closing are crucial for photosynthesis and transpiration.

2. **Identifying the Hormones**:
- **IAA (Indole-3-acetic acid)**: This is a type of auxin, primarily involved in cell elongation and growth regulation, but it does not directly regulate stomatal movements.
- **GA (Gibberellins)**: These hormones are mainly involved in promoting stem elongation, seed germination, and flowering. They do not primarily regulate stomatal movements.
- **Zeatin**: This is a type of cytokinin that promotes cell division and can lead to stomatal opening.
- **ABA (Abscisic Acid)**: This hormone is known as a stress hormone. It is produced in response to stressful conditions (like drought) and plays a crucial role in closing the stomata to conserve water.

3. **Analyzing the Functions**:
- **Stomatal Opening**: Zeatin (cytokinin) promotes the opening of stomata.
- **Stomatal Closure**: ABA (abscisic acid) promotes the closure of stomata during stress conditions.

4. **Conclusion**:
- Based on the analysis, the hormones that regulate stomatal movements are **Zeatin (for opening)** and **ABA (for closure)**. Therefore, the correct answer to the question is **(C) Zeatin and (D) ABA**.

### Final Answer:
The hormones that regulate stomatal movements are (C) Zeatin and (D) ABA.

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