Which of the following statements is true for photosynthesis?

Options

A. Dark reactions occur only in dark
B. Dark and light reactions always occur simultaneously
C. Dark reactions occur only when light reactions stop
D. Dark reactions may also occur in dark

Answer

To determine which statement is true for photosynthesis, let's analyze each option step by step.

### Step 1: Understand Photosynthesis
Photosynthesis is the process by which green plants convert light energy into chemical energy in the form of glucose, using carbon dioxide and water. This process occurs in two main stages: the light reactions and the dark reactions (Calvin cycle).

### Step 2: Analyze Each Statement
1. **Dark reactions only occur in dark**: This statement is false. Dark reactions do not require darkness to occur; they can take place in the presence of light as well.

2. **Dark and light reactions always occur simultaneously**: This statement is misleading. While they can occur at the same time, it is not a requirement. The dark reactions can occur independently of the light reactions as long as the products from the light reactions (ATP and NADPH) are available.

3. **Dark reactions occur only when light reactions are stopped**: This statement is also false. Dark reactions can occur regardless of whether light reactions are happening, as long as the necessary products from the light reactions are present.

4. **Dark reactions may also occur in the dark**: This statement is true. Dark reactions do not require light to proceed; they can occur in the absence of light as long as they have the necessary substrates (ATP and NADPH) produced during the light reactions.

### Conclusion
Based on the analysis, the correct answer is:
**The dark reaction may also occur in the dark.**

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