AP BIOLOGY

Detailed explanation-1: -Carbon dioxide diffuses into leaves during the night (when stomata are open) and is fixed into oxaloacetate by PEP carboxylase, which attaches the carbon dioxide to the three-carbon molecule PEP.

Detailed explanation-2: -PEP carboxylase, which is located in the mesophyll cells, is an essential enzyme in C4 plants. In hot and dry environments, carbon dioxide concentrations inside the leaf fall when the plant closes or partially closes its stomata to reduce water loss from the leaves.

Detailed explanation-3: -What is the role of PEP carboxylase in C4 and CAM plants? PEP carboxylase is essential for carbon fixation in C4 and CAM plants. It is present in the mesophyll cells. It catalyses the initial carbon fixation where PEP acts as an acceptor for CO2, and produces OAA.

Detailed explanation-4: -The enzyme that catalyzes this CO2 fixation is PEP carboxylase or PEPcase. The mesophyll cells of C4 plants lack the enzyme RuBisCO.

Detailed explanation-5: -C4 plants-including maize, sugarcane, and sorghum-avoid photorespiration by using another enzyme called PEP during the first step of carbon fixation. This step takes place in the mesophyll cells that are located close to the stomata where carbon dioxide and oxygen enter the plant.