Cells convert high-calorie molecules such as glucose into energy after the sugar molecules pass through the permeable cell wall. This absorption process occurs as a direct result of insulin being released into the bloodstream by the pancreas. When food is eaten, the pancreas releases insulin, which signals the cells to open up and let the glucose molecules in.
Once they absorb glucose, cells work to turn the molecules into usable energy. The body uses some of the energy immediately and stores the excess for later use. Energy is stored within the chemical bonds of each glucose molecule. Cells obtain energy from the molecules by breaking down these chemical bonds to release the energy.
For the most part, the body gets the energy it needs from the most recently eaten food. However, excess glucose is stored for use when glucose is not readily available in the body. Insulin changes sugar molecules into larger packages of glucose, called glycogen, which are then stored in liver and muscle cells. When the body needs to tap into stored energy, cells retrieve the stored glycogen and break it down to obtain energy, much in the same way that they break down pure glucose molecules for immediate needs.