Respiration is a process that occurs in the cells of all living organisms. It involves breaking down glucose to release energy. There are two types of respiration: aerobic and anaerobic.  (1) respiration requires oxygen to produce energy, whereas (2) respiration does not. During aerobic respiration, glucose reacts with  (3) to produce carbon dioxide, water, and a large amount of energy. The word equation for aerobic respiration is:  (4)+ oxygen → carbon dioxide +  (5) + energy. On the other hand, anaerobic respiration occurs when there is not enough oxygen available, such as during intense exercise. In animals, anaerobic respiration produces  (6) acid and a small amount of energy.