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HomeNEET UGBiologyPhotosynthesis in Higher Plants › O₂ released in photosynthesis comes from:

O₂ released in photosynthesis comes from:

AAtmosphere
BGlucose
CCO₂
DWater (H₂O) — proven by ¹⁸O labeling experiments
Answer & Solution
Correct answer: D. Water (H₂O) — proven by ¹⁸O labeling experiments
Ruben & Kamen experiments with ¹⁸O: labeled water release labeled O₂; labeled CO₂ did not. Confirmed van Niel hypothesis (originally proposed from sulfur bacteria using H₂S instead of H₂O). H₂O is split (photolysis at OEC of PSII) → 2 H⁺ + 2 e⁻ + ½ O₂.
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