In animals, such as humans, the waste products of aerobic respiration are water and carbon dioxide, and the waste product of anaerobic respiration is lactic acid. Aerobic respiration is a series of reactions that sees oxygen being consumed in order to release energy from glucose. Anaerobic respiration occurs when there is an oxygen debt in cells.
Aerobic respiration happens mostly within the mitochondria in eukaryotic cells and the energy found in these cells is in the form of adenosine triphosphate (ATP). Respiration is essentially a production process for ATP. During the process, glucose goes through glycolysis, which creates pyruvate and ATP. If there is oxygen available, this pyruvate is oxygenated, creating acetyl-CoA, and moved on to the mitochondrion where more ATP is produced and both water and carbon dioxide are given. Both the water and the carbon dioxide combine to make carbolic acid, which helps maintain the blood's pH levels.
If there is no oxygen available to the pyruvate after glycolysis, the pyruvate enters a process of fermentation. This is known as anaerobic respiration, and it is used when muscle cells have exhausted their oxygen supply. During aerobic respiration, up to 38 ATP can be produced; however, in anaerobic respiration, only two are produced. When oxygen is available again, NAD+ in the cell forms with the hydrogen in lactic acid to form more ATP.