Water is a critical factor in the process of photosynthesis, as it is one of the reactants involved in the light-dependent reactions. However, its importance goes beyond mere availability as a reactant. The section explains that water stress can lead to the closure of stomata on plant leaves, significantly reducing the uptake of carbon dioxide (CO2) necessary for successful photosynthesis. Furthermore, inadequate water resources can result in wilting of leaves, which diminishes the overall surface area available for gas exchange and metabolic activities. Managing water supply and recognizing its influence on photosynthesis is vital for optimizing plant health and agricultural yield. Therefore, while water may be a reactant in photosynthesis, its role as a facilitator of physiological processes in the plant is equally significant.