Answer :
Final answer:
Rubisco, in the Calvin cycle, incorporates CO2 from the atmosphere into an organic molecule. The cycle happens in three stages: carbon fixation, reduction, and regeneration. It needs to be completed three times to produce a three-carbon GA3P molecule, and six times to make a six-carbon glucose molecule.
Explanation:
The role of rubisco, an enzyme, in the Calvin cycle is best described by option B: Rubisco incorporates CO2 from the atmosphere into an organic molecule. The Calvin cycle, also known as the Calvin-Benson cycle, has three stages. Stage 1 begins with the enzyme Rubisco incorporating carbon dioxide into an organic molecule, in a process known as carbon fixation.
This results in the production of a 3-carbon molecule called 3-phosphoglycerate (3-PGA). It's worth noting that only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule. In the final stage, the remaining G3P molecules are utilized to regenerate ribulose bisphosphate (RuBP), allowing the Calvin cycle to continue.
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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.