( 1 ) Leaf transpiration occurs through stomata , and can be thought of as a necessary `` cost '' associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis . Leaf transpiration occurs through stomata , and can be thought of as a necessary `` cost '' associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis .