Plants lose water from their above ground surfaces in the process of transpiration. Most of this water is lost from stomata, microscopic openings in the leaves. Excess water loss can have a negative effect on the growth, development, and reproduction of a plant. Severe water loss can be fatal. Environmental factors have a major impact on the rate of plant transpiration. text... The curve below illustrates the rate of transpiration related to the percent of open stomata on the leaf of a particular plant. Explain why the curve levels off with increasing percentage of open stomata per area of the leaf.