What is the purpose of cellular respiration?

Cellular respiration is a process that occurs in cells to generate energy for the cell's life processes. The process occurs in the mitochondrion, the bean shaped organelle in the cell that takes glucose, a simple sugar, and oxidizes it with oxygen. The chemical reaction breaks apart the large glucose molecule, releasing free energy which takes the form of ATP, adenosine triphosphate. Carbon dioxide and water are released as waste products. Cellular respiration is the principle energy producer for all animal cells, and for plant cells at night, when the sun goes down and shuts down the other energy making process, photosynthesis. Sometimes, oxygen cannot be delivered fast enough to the cells. Then, the cells employ an alternate energy making process called fermentation. Fermentation produces energy production from the same glucose molecule without the use of oxygen. Between the two energy production methods, cellular respiration produces 38 ATP molecules to fermentation's 2 ATP molecules, causing it to be the more efficient energy production method.