Discuss an Experiment That Used Heavy Isotopes to Elucidate a Metabolic

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The Answer is ¹⁸O was used as a tracer of the fate of the oxygen atoms in water and carbon dioxide to determine whether the atmospheric oxygen produced in photosynthesis arose from H₂O, CO₂, or both:

<sup>18</sup>O was used as a tracer of the fate of the oxygen atoms in water and carbon dioxide to determine whether the atmospheric oxygen produced in photosynthesis arose from H<sub>2</sub>O, CO<sub>2</sub>, or both: If <sup>18</sup>O-labeled CO<sub>2</sub> was presented to a green plant carrying out photosynthesis, none of the <sup>18</sup>O was found in O<sub>2</sub>. Curiously, it was recovered as H<sub>2</sub><sup>18</sup>O. In contrast, when plants fixing CO<sub>2</sub> were equilibrated with H<sub>2</sub><sup>18</sup>O, <sup>18</sup>O<sub>2</sub> was evolved. These latter labeling experiments established that photosynthesis is best described by the equation That is, in the process of photosynthesis, the two oxygen atoms in O<sub>2</sub> come from two H<sub>2</sub>O molecules. One O is lost from CO<sub>2</sub> and appears in H<sub>2</sub>O, and the other O of CO<sub>2</sub> is retained in the carbohydrate product. Two of the four H atoms are accounted for in (CH<sub>2</sub>O), and two reduce the O lost from CO<sub>2</sub> to H<sub>2</sub>O.

If ¹⁸O-labeled CO₂ was presented to a green plant carrying out photosynthesis, none of the ¹⁸O was found in O₂. Curiously, it was recovered as H₂¹⁸O. In contrast, when plants fixing CO₂ were equilibrated with H₂¹⁸O, ¹⁸O₂ was evolved. These latter labeling experiments established that photosynthesis is best described by the equation

That is, in the process of photosynthesis, the two oxygen atoms in O₂ come from two H₂O molecules. One O is lost from CO₂ and appears in H₂O, and the other O of CO₂ is retained in the carbohydrate product. Two of the four H atoms are accounted for in (CH₂O), and two reduce the O lost from CO₂ to H₂O.

Discuss an Experiment That Used Heavy Isotopes to Elucidate a Metabolic

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