Leaves have a large surface area, which means more space to allow CO2 to enter. They are thin so there is less for gases to travel. Leaves contain Stomata; these are small holes found distributed throughout the leaf which open and close, allowing gas exchange. Cells are organised in layers within the leaf. There are air spaces in spongey mesophyll layer which allows gases to effectively diffuse through the leaf. Finally the cells are moist which aids in gas exchange.