In photosynthesis, 12 molecules of water are utilised and 6 molecules of water are released while the formation of one molecule of glucose.
The oxygen atom present in glucose came from

Options

A. the fixed carbon dioxide
B. the water released
C. the water utilised
D. Both (A) & (C)

Answer

To solve the question regarding the origin of the oxygen atom present in glucose during photosynthesis, we can follow these steps:

### Step-by-Step Solution

1. **Understanding Photosynthesis**:
- Photosynthesis is the process by which green plants convert light energy into chemical energy, using sunlight, carbon dioxide (CO₂), and water (H₂O). The overall equation for photosynthesis can be summarized as:
\[ 6 \, \text{CO}_2 + 12 \, \text{H}_2\text{O} \xrightarrow{\text{light, chlorophyll}} C_6H_{12}O_6 + 6 \, \text{O}_2 + 6 \, \text{H}_2\text{O} \]

2. **Identifying Water Utilization and Release**:
- In the process, 12 molecules of water are utilized, and 6 molecules of water are released. This indicates that water is both consumed and produced during photosynthesis.

3. **Analyzing the Oxygen Atoms**:
- The question specifically asks about the oxygen atoms in glucose (C₆H₁₂O₆). In glucose, there are 6 oxygen atoms.

4. **Source of Oxygen in Glucose**:
- The oxygen atoms in glucose come from two sources:
- The water molecules that are utilized in the light-dependent reactions (photolysis of water).
- The carbon dioxide that is fixed during the Calvin cycle (dark reactions).

5. **Determining the Correct Source**:
- The oxygen released during the light reactions comes from the photolysis of water, but the oxygen atoms that are part of glucose are derived from the carbon dioxide that is fixed during the Calvin cycle.
- Therefore, the oxygen in glucose (C₆H₁₂O₆) primarily comes from the carbon dioxide that is used in the photosynthesis process.

6. **Conclusion**:
- The correct answer to the question is that the oxygen atom present in glucose came from the carbon dioxide (CO₂) that was fixed during the photosynthesis process.

### Final Answer:
The oxygen atom present in glucose came from the carbon dioxide (CO₂) used in photosynthesis.