how does the structure of leaf permit gases to diffuse readily between the outside air and the photosynthetic cells?
The leaf has evolved stomata, small pores on the underside of the leaf,to let carbon dioxide in and oxygen out. Stomata are flanked by guard cells, which open the stomata in the morning when light strikes the leaf and close the stomata at night when there is no light available for photosynthesis. All these cells have thin cell walls. By closing the stomata, water transpiration from the leaf is reduced.