It is essentail for both photosynthesis and respiration

Options

A. Sun light
B. Water
C. Oxygen
D. Phytochrome

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks for a factor that is essential for both photosynthesis and respiration.

2. **Identifying Key Processes**:
- **Photosynthesis** is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, using carbon dioxide and water, and releasing oxygen as a byproduct.
- **Respiration** is the process by which cells break down glucose and other organic molecules to produce energy, consuming oxygen and releasing carbon dioxide.

3. **Evaluating Possible Answers**:
- **Sunlight**: Essential for photosynthesis but not for respiration.
- **Water**: Necessary for photosynthesis but not directly for respiration.
- **Oxygen**: A byproduct of photosynthesis and essential for respiration, but not needed for photosynthesis itself.
- **Phytochrome**: A pigment involved in the regulation of plant processes, including the regulation of gene expression related to both photosynthesis and respiration.

4. **Conclusion**: The correct answer is **phytochrome**, as it plays a role in regulating the expression of genes that are important for both photosynthesis and respiration.

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