IMMUNOLOGY

Detailed explanation-1: -PEP (phosphoenol pyruvate) is the CO2 acceptor in C4 plants. The molecule accepts the CO2 and allows the fixation of it. This results in the fixation of the gas at lower concentrations as RUBISCO does not bind CO2 at lower concentrations.

Detailed explanation-2: -CO 2 is initially fixed in the mesophyll cells by the enzyme PEP carboxylase which reacts the three carbon phosphoenolpyruvate (PEP) with CO 2 to form the four carbon oxaloacetic acid (OAA).

Detailed explanation-3: -In C4 plants the carbon dioxide is initially fixed into four carbon atom containing organic acids, like malate and oxalo acetic acid. The carbon dioxide is fixed initially in the chloroplasts of spongy mesophyll tissue by the enzyme PEP carboxylase.

Detailed explanation-4: -The enzyme that catalyzes this CO2 fixation is PEP carboxylase or PEPcase.