Respiration is part of the metabolic process where the nutrients are converted into useful energy for regular cell activities. It is in two-mode depending on the presence or absence of oxygen. Aerobic respiration is the one where oxygen is involved and anaerobic respiration is the process where oxygen is absent.

Respiration is generally considered catabolic as the complex compounds are broken into simpler forms to produce energy. Although, respiration has been found to be both catabolic and anabolic. Protein and fatty acids are broken down into acetyl-CoA, which will be used in the aerobic respiratory process. This acetyl-CoA can also be used in the process of manufacturing fatty acids and protein by stopping the respiratory pathway as per the need of the cell. This process is anabolic as compounds are synthesized. Thus, the respiratory process is considered to be amphibolic - anabolic as well as catabolic.