The most important energy supply molecule for all living things is

The sun is the ultimate source of energy in any ecosystem. Solar energy is captured by plants to produce food in the process of photosynthesis. During photosynthesis carbon dioxide and water using solar energy is converted into to glucose and oxygen.  In glucose molecules energy is stored to carry out life processes of plants.  

Other organisms, in turn, feed on plants and break down glucose molecules in the process of cellular respiration to release energy. The released energy is utilized by the cells to synthesize a chemical molecule, Adenosine triphosphate (ATP). ATP is the energy currency for cells. ATP supply energy for all the metabolic activities of organisms.