Which of the following stimulates growth or cell enlargement ?

Options

A. Gibberellin
B. Auxin
C. Cytokinin
D. Ethylene.

Answer

To determine which of the following stimulates growth or cell enlargement, we can analyze each option provided:

1. **Gibberellin**: This plant hormone is primarily known for promoting stem elongation and flowering. While it does play a role in growth, its main function is not specifically cell enlargement.

2. **Auxin**: Auxin is a key plant hormone that significantly stimulates growth and cell enlargement. It works by increasing the permeability of cell membranes, which enhances water uptake by cells. This increase in water causes cells to swell and enlarge. Additionally, auxin enhances the plasticity of cell walls, allowing for further expansion.

3. **Cytokinin**: Cytokinins are hormones that primarily promote cell division rather than enlargement. They are involved in various processes such as shoot formation and delay of leaf senescence, but they do not directly stimulate cell enlargement.

4. **Ethylene**: Ethylene is a plant hormone that is mainly associated with the ripening of fruits and the regulation of other processes like leaf abscission. It does not play a direct role in stimulating growth or cell enlargement.

Based on this analysis, the correct answer to the question is **Auxin**.

### Step-by-Step Solution:
1. **Identify the hormones listed**: The options are gibberellin, auxin, cytokinin, and ethylene.
2. **Analyze each hormone's function**:
- Gibberellin: Promotes flowering and stem elongation.
- Auxin: Stimulates growth and cell enlargement by increasing cell wall plasticity and water uptake.
- Cytokinin: Promotes cell division.
- Ethylene: Promotes fruit ripening.
3. **Determine which hormone specifically stimulates growth or cell enlargement**: Auxin is known for its role in cell enlargement and growth stimulation.
4. **Conclude with the correct answer**: The hormone that stimulates growth or cell enlargement is **Auxin**.