The two main types of cellular respiration are aerobic and anaerobic respiration. Aerobic respiration requires oxygen and primarily occurs in the mitochondria of cells, producing ATP, carbon dioxide, and water as byproducts. It is the most efficient form of energy production, generating up to 36 ATP molecules from one glucose molecule. In contrast, anaerobic respiration occurs in the absence of oxygen, resulting in the production of energy through processes like fermentation, leading to byproducts such as lactic acid or ethanol. Anaerobic respiration is less efficient, yielding only 2 ATP molecules per glucose.