Cholodony and Went effect is due to
(a) IAA
(b) GA
(c) Cytokinin
(d) ABA

Options

A. IAA
B. GA
C. Cytokinin
D. ABA.

Answer

To solve the question regarding the Cholodony and Went effect, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks about the cause of the Cholodony and Went effect, which is related to plant growth and movements.

2. **Identify Key Terms**: The Cholodony and Went effect is associated with gravitropism, which is the growth response of a plant to gravity.

3. **Consider the Options**: The options given are:
- (a) IAA (Indole-3-acetic acid)
- (b) GA (Gibberellic acid)
- (c) Cytokinin
- (d) ABA (Abscisic acid)

4. **Analyze Each Option**:
- **IAA (Indole-3-acetic acid)**: This is a type of auxin that plays a crucial role in plant growth and is known to accumulate on the lower side of a plant stem in response to gravity, leading to differential growth.
- **GA (Gibberellic acid)**: This hormone is involved in various growth processes but is not specifically related to the Cholodony and Went effect.
- **Cytokinin**: This hormone promotes cell division but does not directly relate to the Cholodony and Went effect.
- **ABA (Abscisic acid)**: This hormone is primarily involved in stress responses and does not relate to the Cholodony and Went effect.

5. **Conclusion**: Based on the analysis, the Cholodony and Went effect is due to the accumulation of IAA on the lower side of the stem, which causes differential growth and results in the bending of the plant. Therefore, the correct answer is (a) IAA.

### Final Answer:
(a) IAA