If green plant cells are incubated with `O^(18)`labelled `CO_(2)`. Which of the following molecules will become radioactive when the cells are exposed to light?

Options

A. ATP
B. Water
C. Sugar
D. `O_(2)`

Answer

To solve the question regarding which molecules will become radioactive when green plant cells are incubated with \(O^{18}\)-labeled \(CO_2\) and exposed to light, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Process of Photosynthesis**:
Photosynthesis is the process by which green plants convert carbon dioxide and water into glucose and oxygen using sunlight. The general equation for photosynthesis is:
\[ 6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2 \]

2. **Identify the Source of Oxygen**:
In the photosynthesis equation, the oxygen produced (\(O_2\)) comes from water (\(H_2O\)), not from carbon dioxide. This is a crucial point because it determines where the radioactive oxygen will end up.

3. **Analyze the Radioactive Labeling**:
Since we are using \(O^{18}\)-labeled \(CO_2\), the carbon dioxide has a radioactive isotope of oxygen. However, during photosynthesis, the oxygen produced as a byproduct does not come from the \(CO_2\) but from the water.

4. **Determine the Fate of the Radioactive Oxygen**:
The radioactive oxygen from the \(O^{18}\)-labeled \(CO_2\) will be incorporated into the glucose (sugar) molecule during the photosynthesis process. Therefore, the sugar produced will contain the radioactive oxygen.

5. **Conclusion**:
Based on the above analysis, the molecule that will become radioactive when the cells are exposed to light is **sugar** (glucose).

### Final Answer:
The correct option is **sugar**.

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