To identify the molecule that first reacts with CO₂ in the light-independent reactions of photosynthesis, Calvin and Benson manipulated the carbon-fixation cycle by either elminating CO₂ or light from cultures of photosynthetic algae. Which of the following statements best predicts the immediate effects of these manipulations on the concentration of the molecule that initially reacts with CO₂? A) The concentration would decrease when either the CO₂ or light is eliminated. B) The concentration would increase when either the CO₂ or light is eliminated. C) The concentration would decrease when the CO₂ is eliminated, but increase when the light is eliminated. D) The concentration would increase when the CO₂ is eliminated, but decrease when the light is eliminated.

Question

Quizplus · Accepted Answer

The molecule that initially reacts with CO2 (carbon dioxide) in the light-independent reactions (Calvin cycle) of photosynthesis is RuBP (ribulose bisphosphate). If CO2 is eliminated, RuBP accumulates because it is not being used to fix carbon. If light is eliminated, the overall process of photosynthesis slows down or stops, leading to a decrease in the regeneration of RuBP, thus its concentration would decrease.

To Identify the Molecule That First Reacts with CO2 in the Light-Independent

To Identify the Molecule That First Reacts with CO₂ in the Light-Independent