The document discusses photosynthesis in C3 and C4 plants. It shows that willow and maize plants will both survive under a sealed cover individually, but only the willow survives when the two are combined, due to the maize plant using oxygen during photosynthesis. It then examines the differences in carbon fixation pathways between C3 and C4 plants, including their A-Ci curves and leaf anatomy, showing C4 plants have adaptations that allow them to more efficiently fix carbon in hot, dry environments. The document depicts the pathways that allow C4 plants like maize to concentrate CO2 around rubisco through compartmentalization between mesophyll and bundle sheath cells.