A suspension of algae is incubated in a flask in the presence of both light and CO₂.When it is transferred to the dark, the reduction of 3-phosphoglycerate (3PG) to glyceraldehyde 3-phosphate (G3P) slows and then stops.At the same time, the concentration of ribulose 1,5-bisphosphate (RuBP) declines.Why does the RuBP concentration decline? A) RuBP is more rapidly metabolized in the dark. B) RuBP is used up in making more 3PG. C) Sugar is no longer generated from G3P. D) The levels of oxygen drop. E) RuBP needs to be regenerated from G3P.

Question

Quizplus · Accepted Answer

RuBP is required for the fixation of CO2 in photosynthesis, and in the dark, there is no CO2 fixation taking place. However, RuBP is needed for the regeneration of G3P, which is a crucial intermediate in the production of sugars in the dark. Therefore, the decline in RuBP concentration is due to its utilization in the regeneration of G3P.

A Suspension of Algae Is Incubated in a Flask in the Presence