Tropic movements are caused by

Options

A. Cell division
B. Cell elongation
C. Loss of water
D. Gain of water.

Answer

**Step-by-Step Solution:**

1. **Understanding Tropic Movements**:
- Tropic movements are directional growth movements in plants in response to external stimuli such as light (phototropism), gravity (gravitropism), and water (hydrotropism).

2. **Identifying the Cause of Tropic Movements**:
- The primary cause of tropic movements is the differential growth of plant cells. This means that certain areas of the plant grow faster than others in response to a stimulus.

3. **Cell Elongation**:
- The key mechanism behind tropic movements is cell elongation. When a plant is exposed to a stimulus, such as light, the cells on one side of the plant may elongate more than those on the opposite side.

4. **Example of Phototropism**:
- In phototropism, when a plant is exposed to light from one direction, the cells on the shaded side elongate more than the cells on the illuminated side. This differential elongation causes the plant to bend towards the light source.

5. **Conclusion**:
- Therefore, the correct answer to the question "Tropic movements are caused by" is **cell elongation**. Other factors such as cell division or changes in water content do not directly cause tropic movements.

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