In Cellular Respiration, cells use oxygen to release energy stored in sugars such as glucose. In fact, most of the energy used by the cells in your body is provided by cellular respiration. In fact, most of the energy used by the cells in your body is provided by cellular respiration. The process begins when glucose in the cytoplasm is broken down into smaller molecules. This releases a small amount of energy. These molecules then move into the mitochondria. At the same time, oxygen enters the cell and travels into the mitochondria. As the smaller molecules are broken down even further, hydrogen is released along with a large amount of energy. The hydrogen combines with oxygen to make water. The products, are energy, carbon dioxide, and water.