The chemical process that converts sugar into energy in living organisms is called cellular respiration. This process primarily occurs in the mitochondria of cells and involves several stages, including glycolysis, the Krebs cycle, and oxidative phosphorylation. During cellular respiration, glucose (a simple sugar) is broken down in the presence of oxygen to produce adenosine triphosphate (ATP), the energy currency of the cell. As glucose is metabolized, byproducts such as carbon dioxide and water are formed. This process is crucial for providing energy to sustain various biological functions, growth, and maintenance of cells in living organisms.