I don't remember seeing a C4 pathway Q but there are many diff versions. I studied both C3 & C4. This may help:
"C4 carbon fixation is a metabolic pathway found in some land plants (C4 plants). They have a competitive advantage over plants possessing the more common C3 carbon fixation pathway under conditions of drought, high temperatures and nitrogen or carbon dioxide limitation. The C4 plants possess a characteristic leaf anatomy. Their vascular bundles are surrounded by two rings of cells. The inner ring, called Bundle Sheath Cells, contain starch-rich chloroplasts lacking grana which differ from those in mesophyll cells present as the outer ring. Hence, the chloroplasts are called dimorphic. This peculiar anatomy is called Kranz Anatomy (Kranz-Crown/Halo). The C4 cycle allows for a spacial separation of carbon uptake from carbon fixation, thus allowing C4 plants to increase concentration of CO2 within their leaves. This increases the amount of photosynthesis and decreases the chances of photorespiration, a harmful process in which organic material and energy is lost from the plant due to high concentrations of oxygen. "