alleryO₂ 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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