The most common photosynthetic pathway used by plants is C3 carbon fixation, usually shortened to C3. It is named for the three-carbon compound, 3-phosphoglycerate, formed in the first stable step of carbon fixation.
In C3 photosynthesis, the enzyme Rubisco adds carbon dioxide to the five-carbon molecule ribulose bisphosphate, or RuBP. The unstable intermediate splits into two molecules of 3-phosphoglycerate, which then enter the Calvin–Benson cycle and are used to build carbohydrates.
C3 plants include major crops such as wheat, rice, barley, soybeans, and potatoes. The pathway works well under moderate light, moderate temperatures, and adequate water, conditions found across much of the world. C3 plants are considered the most common plant type and account for most plant biomass.
C4 and CAM pathways evolved adaptations that reduce photorespiration in hot, bright, or dry environments. C4 plants include maize and sugarcane, while CAM plants include many cacti and other succulents. C3 is also a frequent source of confusion because all plants using C4 or CAM still perform the C3 reactions of the Calvin cycle after carbon dioxide is concentrated.