The energy used in cellular respiration originates from the combination of food that humans feed on and oxygen. Energy in the form of adenosine triphosphate (ATP) is released when bonds of organic molecules are broken.
All living organisms require energy for metabolism. Cells obtain energy from nutrients ingested in the form of glucose. This process is referred to as cellular respiration. Here, large molecules are broken down into smaller molecules. Animal and plant cells use nutrients such as amino acids, sugars and fatty acids to generate energy. The process occurs in the presence of oxygen, which acts as the oxidizing agent.
There are two types of cellular respiration: aerobic and anaerobic. Aerobic respiration needs oxygen to generate energy in the form of ATP. The products of aerobic respiration are water and carbon dioxide. On the other hand, no oxygen is needed in anaerobic respiration. In this regard, aerobic respiration is more than 10 times more efficient in generating energy than anaerobic respiration is. For each molecule of glucose, aerobic respiration yields two molecules of ATP. Cells then use the generated energy in processes such as cell regeneration, biosynthesis and locomotion. Any extra energy is stored within reservoirs in the cells.