Pigment phytochrome is involved in

Options

A. phototropism
B. photorespiration
C. photoperiodism
D. geotropism

Answer

To answer the question "Pigment phytochrome is involved in," we will analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Phytochrome**:
- Phytochrome is a photoreceptor pigment in plants that is sensitive to light, particularly red and far-red light. It plays a crucial role in regulating various physiological processes in plants.

2. **Evaluating Option 1: Phototropism**:
- Phototropism refers to the growth of a plant in response to light direction. While light is involved, phototropism primarily involves other photoreceptors, not specifically phytochrome. Therefore, this option is incorrect.

3. **Evaluating Option 2: Photorespiration**:
- Photorespiration is a process that occurs in plants where oxygen is consumed and carbon dioxide is released, often occurring when the stomata are closed. This process is not directly regulated by phytochrome. Thus, this option is also incorrect.

4. **Evaluating Option 3: Photoperiodism**:
- Photoperiodism is the response of plants to the relative lengths of light and dark periods. Phytochrome is crucial in this process as it helps plants detect changes in light duration, influencing flowering and other developmental processes. Therefore, this option is correct.

5. **Evaluating Option 4: Geotropism**:
- Geotropism refers to the growth of plants in response to gravity. This phenomenon is not influenced by phytochrome but by other mechanisms. Hence, this option is incorrect.

### Conclusion:
The correct answer is **Option 3: Photoperiodism**, as phytochrome is directly involved in the plant's response to the length of light and dark periods.

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