What are C4 plants?
What special features do they have?
What do they do?
They are plants which form a four-carbon compound as its product in the Calvin cycle.
They have bundle sheath cells tightly packed around the veins, and mesophyll cells between the bundle sheath and the leaf surface.
The mesophyll cells essentially shield the bundle sheaths from O2 and pump CO2 into the bundle sheath, keeping the CO2 concentration high enough for rubisco to bind carbon dioxide rather than oxygen.