Answer :
Final answer:
The Calvin Cycle begins with the combination of CO2 and RuBP. It utilizes ATP and NADPH produced in the light-dependent reactions and goes through stages of fixation, reduction, and regeneration, producing glucose and regenerating RuBP over several cycles.
Explanation:
The Calvin Cycle begins when CO2 combines with a five-carbon carbohydrate called RuBP (ribulose bisphosphate). The cycle occurs in the stroma of chloroplasts and can proceed during both day and night. Photosynthesis in plants involves this critical cycle, using energy stored in ATP and NADPH from the light-dependent reactions.
There are three basic stages in the Calvin cycle: fixation, reduction, and regeneration. During the fixation stage, the enzyme RuBisCO incorporates CO2 into an organic molecule, 3-PGA (3-phosphoglycerate). In the reduction stage, ATP and NADPH are used to convert 3-PGA into G3P (Glyceraldehyde-3-phosphate), which stores the energy captured from photosynthesis. Finally, in the regeneration stage, ATP is again utilized to regenerate RuBP from G3P, allowing the cycle to continue and fixing more CO2.
Overall, a single G3P molecule exits the cycle to contribute to the formation of carbohydrates like glucose (C6H12O6) after three turns of the cycle. Since glucose is a six-carbon sugar, the Calvin cycle must spin six times to produce one molecule of glucose. The remaining G3P molecules are used to regenerate RuBP, which readies the system for more CO2 fixation.