During photosynthesis

Answer

### Step-by-Step Solution

1. **Understanding the Source of Oxygen in Photosynthesis**:
- The statement claims that oxygen comes from carbon dioxide during photosynthesis. This is incorrect.
- In reality, the oxygen produced during photosynthesis originates from the splitting of water molecules (H₂O).

2. **The Process of Water Splitting**:
- During photosynthesis, specifically in the light-dependent reactions, water molecules are split into oxygen, protons (H⁺ ions), and electrons.
- The reaction can be summarized as:
\[ 2 H₂O \rightarrow 4 H⁺ + 4 e⁻ + O₂ \]
- This process occurs in the thylakoid membranes of chloroplasts, specifically in the lumen of the thylakoids.

3. **Role of the Oxygen Evolving Complex**:
- The splitting of water is facilitated by the oxygen-evolving complex (OEC), which requires certain activators like manganese and chloride ions.

4. **ATP Formation and Consumption**:
- The question also mentions ATP formation during photosynthesis. While ATP is indeed produced during the light-dependent reactions, it is also consumed in the light-independent reactions (Calvin Cycle) for the synthesis of glucose.
- Therefore, it is misleading to say that ATP is solely formed during photosynthesis.

5. **Water's Role in Photosynthesis**:
- The statement that water is not required as a reactant but only as a medium is incorrect. Water is essential as a reactant in the photosynthetic process.

6. **Conclusion**:
- All the statements provided in the question are incorrect. The correct understanding is that oxygen comes from water, ATP is both formed and consumed, and water is a crucial reactant in photosynthesis.

### Final Answer
All the statements regarding the source of oxygen, the role of ATP, and the role of water during photosynthesis are incorrect.

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