Photosynthesis cycle

In the first step of the cycle CO2reacts with RuBPto produce two 3-carbon molecules of 3-phosphoglyceric acid (3-PGA). This is the origin of the designation C3 or C3in the literature for the cycle and for the plants that use this cycle. The entire process, from light energy capture to sugar production occurs within the chloroplast.

Photosynthesis as a whole is not considered a cycle. The process of carbon fixation is dependent on the Calvin cycle, which is called a cycle because it “starts” (OK, a cycle can be said to start anywhere, but…) with ribulose bisphosphate, which gets converted into two molecules of 3-phosphoglycerate (via the addition of carbon dioxide).

It involves producing a three-carbon compound called 3-phosphoglyceric acid during the Calvin Cycle, which goes on to become glucose. C4 photosynthesis, on the other hand, produces a four-carbon intermediate compound, which splits into carbon dioxide and a three-carbon compound during the Calvin Cycle.

The process of photosynthesis is commonly written as: 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2. This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products.