If photosynthesizing green algae are provided with CO₂ synthesized with heavy oxygen (¹⁸O), later analysis will show that all but one of the following compounds produced by the algae contain the ¹⁸O label. That one is
A) 3-phosphoglycerate.
B) glyceraldehyde 3-phosphate (G3P).
C) glucose.
D) ribulose bisphosphate (RuBP).
E) O₂.

Question

Quizplus · Accepted Answer

During photosynthesis, the oxygen atoms in the CO₂ molecules do not end up in the O₂ produced. Instead, the O₂ released comes from the splitting of water (H₂O) molecules in the light-dependent reactions, not from the carbon dioxide (CO₂) used in the Calvin cycle. Therefore, if CO₂ with ¹⁸O is used, the ¹⁸O would be incorporated into the carbon fixation products (3-phosphoglycerate, glyceraldehyde 3-phosphate (G3P), glucose, and ribulose bisphosphate (RuBP)) but not in the molecular oxygen (O₂) released.

If Photosynthesizing Green Algae Are Provided with CO₂ Synthesized with Heavy