Phytochrome is involved in

Options

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

Answer

To solve the question "Phytochrome is involved in", we will analyze the options provided and determine the correct answer based on the function of phytochromes in plants.

### Step-by-Step Solution:

1. **Understanding Phytochromes**:
- Phytochromes are photoreceptors found in plants. They are sensitive to light, particularly to red and far-red wavelengths.

2. **Identifying Functions**:
- Phytochromes play a crucial role in various physiological processes in plants, including:
- **Phototropism**: Growth of plants towards light.
- **Photorrespiration**: A process that occurs in plants when they take up oxygen and release carbon dioxide, often in light.
- **Photoperiodism**: The response of plants to the relative lengths of light and dark periods, which affects flowering and other developmental processes.
- **Geotropism**: The growth of plant roots and shoots in response to gravity.

3. **Analyzing the Options**:
- **Phototropism**: While phytochromes may influence growth direction, they are not the primary factor.
- **Photorrespiration**: This is more related to the metabolic processes in plants rather than light detection.
- **Photoperiodism**: This is a key function of phytochromes, as they help regulate flowering based on day and night duration.
- **Geotropism**: This is primarily influenced by gravity rather than light.

4. **Conclusion**:
- Based on the analysis, the most relevant function of phytochromes is **Photoperiodism**. They are crucial for regulating flowering in response to the duration of light and dark periods.

### Final Answer:
Phytochrome is involved in **Photoperiodism**.