Sunlight is considered essential for photosynthesis because it provides the energy needed to drive the process. During the light-dependent reactions of photosynthesis, light energy is absorbed by chlorophyll and other pigments in plant cells. This energy is used to split water molecules, releasing oxygen and generating high-energy molecules such as ATP and NADPH. These energy-rich molecules are then utilized in the light-independent reactions (Calvin cycle) to convert carbon dioxide into glucose. Without sunlight, the light-dependent reactions cannot occur, and the overall photosynthetic process is hindered, emphasizing the indispensable role of sunlight in powering the synthesis of organic molecules in plants.