AP BIOLOGY

Detailed explanation-1: -The key step in the Calvin cycle is the event that reduces CO2. CO2 binds to RuBP in the key process called carbon fixation, forming two-three carbon molecules of phosphoglycerate.

Detailed explanation-2: -Stage 1: Fixation For each CO2 molecule that reacts with one RuBP, two molecules of 3-phosphoglyceric acid (3-PGA) form. 3-PGA has three carbons and one phosphate. Each turn of the cycle involves only one RuBP and one carbon dioxide and forms two molecules of 3-PGA.

Detailed explanation-3: -In the second stage, ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar, glyceraldehyde-3-phosphate (G3P).

Detailed explanation-4: -Using the energy carriers formed in the first stage of photosynthesis, the Calvin cycle reactions fix CO2 from the environment to build carbohydrate molecules. An enzyme, RuBisCO, catalyzes the fixation reaction, by combining CO2 with RuBP.

Detailed explanation-5: -The carbohydrate products of the Calvin cycle are three-carbon sugar phosphate molecules, or “triose phosphates", namely, glyceraldehyde-3-phosphate (G3P).