C4 plants utilize a form of carbon fixation that has a molecule with 4 carbons present as a first product. C4 carbon fixation is a more complicated version of C3 carbon fixation. As opposed to C3 carbon fixation, C4 carbon fixation does not allow for RuBisCO to add oxygen in photorespiration. More effective processes allow for this to occur and make C4 carbon fixation far more effective than C3 carbon fixation in many conditions despite a higher requirement of energy (ATP). C4 plants are most effective in hot and dry environments. In the C4 carbon fixation pathway, a process occurs in mesophyll cells wherein carbon dioxide binds to a phosphoenolpyruvate. The product of this process releases carbon dioxide for use in the C3 carbon fixation process. Most grasses like the one pictured above are C4 plants.