The oxygen evolved as a by-product during photosynthesis comes from

Options

A. water
B. carbon dioxide
C. glucose
D. chlorophyll

Answer

**Step-by-Step Solution:**

1. **Understanding Photosynthesis**: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide and water to produce glucose and oxygen.

2. **Identifying By-products**: During photosynthesis, oxygen is released as a by-product. This means it is produced alongside the main product, which is glucose.

3. **Sources of Oxygen**: The question asks where the oxygen that is evolved during photosynthesis comes from. The possible options are:
- Water (H2O)
- Carbon dioxide (CO2)
- Glucose (C6H12O6)
- Chlorophyll

4. **Scientific Investigation**: To determine the source of the oxygen, scientists have conducted experiments. One notable experiment was done by Cornelius Van Niel, who used a radioactive isotope of oxygen (O-18) in water (H2O).

5. **Results of the Experiment**: After conducting the experiment, it was observed that the oxygen released during photosynthesis contained the O-18 isotope, indicating that the oxygen evolved comes from water.

6. **Photosynthesis Reaction**: In the light-dependent reactions of photosynthesis, specifically in a process called photolysis, water molecules (H2O) are split into hydrogen ions (H+), electrons, and oxygen gas (O2). This reaction occurs in Photosystem II.

7. **Conclusion**: Based on the scientific evidence and the process of photosynthesis, we conclude that the oxygen released as a by-product during photosynthesis comes from water (H2O).

**Final Answer**: The oxygen evolved as a by-product during photosynthesis comes from water (H2O).

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