Discussion of gas exchange in leaves. So the photosynthesizing leaf loses substantial amount of water by evaporation. This transpired water must be replaced by the transport of more water from the soil to the leaves through the xylem of the roots and stem. Importance Transpiration is not simply a hazard of plant life. Light Plants transpire more rapidly in the light than in the dark.
Light also speeds up transpiration by warming the leaf.
Temperature Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. The rate of diffusion of any substance increases as the difference in concentration of the substances in the two regions increases. When the surrounding air is dry, diffusion of water out of the leaf goes on more rapidly. When there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration. When a breeze is present, the humid air is carried away and replaced by drier air.