The plant hormone responsible for phototropism is:

### Understanding Phototropism Phototropism is a plant growth response where the plant bends toward a light source. This phenomenon is primarily controlled by plant hormones called **Auxins**. ### Mechanism of Action 1. **Detection**: The tip of the plant stem (coleoptile) detects the direction of light. 2. **Redistribution**: When light strikes one side of the stem, auxins migrate toward the **shaded side**. 3. **Cell Elongation**: The high concentration of auxin on the shaded side stimulates cells to elongate more rapidly than the cells on the lighted side. 4. **Bending**: Because one side grows faster than the other, the stem physically curves toward the light source. ### Comparison with Other Hormones - **Gibberellins**: Primarily involved in stem elongation, seed germination, and flowering. - **Cytokinins**: Promote cell division (cytokinesis) and delay leaf senescence. - **Abscisic acid (ABA)**: Acts as a growth inhibitor, promoting seed dormancy and stomatal closure during stress. Therefore, the correct hormone responsible for phototropism is **Auxin**.