The correct answer is B) Rubisco incorporates CO2 from the atmosphere into an organic molecule
RuBP oxygenase-carboxylase or rubisco enzyme is an enzyme that acts during the first stage of the Calvin cycle (light-independent or dark reactions of photosynthesis). Its role is in the process of carbon fixation where rubisco incorporates carbon dioxide into an organic molecule (CO2 combines with a five-carbon acceptor molecule, ribulose-1,5-bisphosphate – RuBP).
Besides of using CO2 as a substrate, rubisco sometimes uses O2. This is a reaction called photorespiration, which leads to the loss of already-fixed carbon, waste of energy and decrease in sugar synthesis.
