Explain how the structure of a leaf is adapted for efficient gas exchange.

Stomata are pores on the leaf surface that allow CO₂ to enter and O₂ and H₂O to leave. They can open and close, so the plant controls the rate of gas exchange and limits water loss. The spongy mesophyll layer contains large intercellular air spaces; these increase the surface area available for gas exchange. The mesophyll cells are arranged so that their large surface area is in contact with the air spaces, giving a short diffusion distance for gases. Leaves are thin and flat, which further reduces the distance gases must diffuse to reach all cells.