Bending of stem towards light is

Options

A. Photoperiodism
B. Heliotropism
C. Photonasty
D. Hydrotropism.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the phenomenon where a plant stem bends towards light. This behavior is a response to light stimuli.

2. **Identifying the Options**: The options provided are:
- A) Photoperiodism
- B) Heliotropism
- C) Photonasty
- D) Hydrotropism

3. **Analyzing Each Option**:
- **Photoperiodism**: This refers to the physiological reactions of plants to the lengths of day and night. It primarily affects processes like flowering, not the bending of stems towards light.
- **Heliotropism**: This is the growth movement of a plant in response to sunlight. It specifically refers to the bending of the stem towards the direction of light.
- **Photonasty**: This is a type of movement in plants that occurs in response to light but is not directional. It refers to movements like opening and closing of flowers or leaves, rather than bending towards light.
- **Hydrotropism**: This refers to the growth of plant roots towards moisture or water, not light.

4. **Determining the Correct Answer**: Based on the definitions:
- The bending of the stem towards light is best described by **heliotropism** (Option B).

5. **Conclusion**: Therefore, the correct answer to the question "Bending of stem towards light is" is **heliotropism**.

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