Which of the following occurs during dark phase of photosynthesis ?

Options

A. Hydrogen is released
B. ATP is produced
C. Molecular oxygen is released
D. PGAL is synthesized

Answer

To answer the question "Which of the following occurs during the dark phase of photosynthesis?", we need to analyze the given options in relation to the two phases of photosynthesis: the light reactions and the dark reactions (Calvin cycle).

### Step-by-Step Solution:

1. **Understanding the Phases of Photosynthesis**:
- Photosynthesis consists of two main phases: the light reactions and the dark reactions (Calvin cycle).
- The light reactions occur in the presence of sunlight and involve the conversion of light energy into chemical energy (ATP and NADPH), along with the splitting of water molecules (photolysis) which releases oxygen.

2. **Analyzing the Options**:
- **Option 1: Release of Hydrogen**:
- This occurs during the light reactions when water is split (photolysis). Thus, it does not occur during the dark phase.
- **Option 2: ATP Production**:
- ATP is produced during the light reactions as a result of the energy captured from sunlight. Therefore, this also does not occur during the dark phase.
- **Option 3: Molecular Oxygen Release**:
- The release of oxygen (O2) happens during the light reactions due to the photolysis of water. Hence, this option is also not correct for the dark phase.
- **Option 4: PGA-L Synthesis**:
- PGA-L (Phosphoglyceraldehyde) is the first stable product of the Calvin cycle, which occurs during the dark reactions. This process involves the fixation of carbon dioxide and the synthesis of three-carbon compounds.

3. **Conclusion**:
- Among the given options, the only process that occurs during the dark phase of photosynthesis is the synthesis of PGA-L. Therefore, the correct answer is that PGA-L is synthesized during the dark phase.

### Final Answer:
**PGA-L is synthesized during the dark phase of photosynthesis.**