Study of phototropic lead to the discovery of

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Phototropism**:
- Phototropism refers to the growth of a plant in response to light. The term "photo" means light, and "tropism" refers to movement or growth toward or away from a stimulus.

2. **Identifying the Role of Light**:
- In phototropism, plants can grow towards light (positive phototropism) or away from light (negative phototropism). This growth response is crucial for plants to maximize their exposure to sunlight for photosynthesis.

3. **Historical Discovery**:
- The phenomenon of phototropism was first studied by Charles Darwin. He conducted experiments that demonstrated how plants respond to light.

4. **Discovery of Auxin**:
- During his studies, Darwin discovered that a specific plant hormone, known as auxin, is produced at the tip of the plant stem. Auxin is responsible for regulating plant growth and is crucial in the process of phototropism.

5. **Conclusion**:
- Therefore, the study of phototropism led to the discovery of auxin, which is a key plant hormone involved in growth responses to light.

**Final Answer**: The study of phototropism led to the discovery of auxin.

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