${\mathrm{C}}_4$ plants show chloroplast dimorphism. Mesophyll cells have PEPcase but do not have RuBisCO, while the bundle sheath cells have RuBisCO but do not have PEPcase. The ATP synthase enzyme consists of two parts: one called the ${\mathrm{F}}_0$ is embedded in the thylakoid membrane and forms a transmembrane channel that carries out facilitated diffusion of protons across the membrane. The other portion is called ${\mathrm{F1,}}_{}$ and it protrudes on the outer surface of the thylakoid membrane on the side that faces the stroma. The membrane or lamellae of the grana have both PS I and PS II, while the stromal lamellae membranes lack PS II as well as NADP reductase enzyme. RuBisCO has much greater affinity for carbon dioxide and oxygen when they are nearly equal. This binding is competitive. It is the relative concentration of oxygen and carbon dioxide that determines which of the two will bind to the enzyme.