The breakdown of carbohydrates into energy can occur by a variety of chemical pathways. Some of these pathways are aerobic and some are not. While oxygen-based pathways are the respiratory method of choice because of their greater efficiency, there are many instances in which anaerobic respiration has a useful function, or even an advantage.
Respiration, not to be confused with breathing, is any process by which a cell releases energy from the chemical bonds of complex molecules, such as glucose. There are many chemical pathways by which respiration occurs. Some of these pathways require oxygen and are called aerobic respiration. Pathways that do not require oxygen are called anaerobic respiration.
Aerobic and anaerobic respiration both begin with glycolysis, the first stage in the breakdown of glucose. This process generates two molecules of ATP, a major energy carrier molecule. Glycolysis is an anaerobic process and can then be followed by an aerobic or anaerobic process.
Aerobic respiration is the respiratory pathway of choice for oxygen-dependent organisms because of its greater efficiency. One molecule of glucose can be converted into up to 32 molecules of ATP during aerobic respiration, but only two molecules of ATP per glucose molecule are gained from anaerobic respiration.
Anaerobic respiration can also follow glycolysis and generates two molecules of ATP and produces lactic acid as a byproduct. If lactic acid builds up in muscle tissue, it can cause pain and cramping.
Assisting Aerobic Respiration
Pyruvic acid is a byproduct of glycolysis. Anaerobic respiration can metabolise pyruvic acid, and in the process, regenerate enzymes necessary for glycolysis, facilitating further aerobic respiration.
Anaerobic Origins of Life
Anaerobic respiration is the first of all respiratory processes; 3.5 billion years ago, atmospheric oxygen was lacking and the first respiratory chemical pathways were anaerobic. While this is not an advantage precisely, it is an importance of anaerobic respiration.
Anaerobic Respiration as a Fail-Safe Mechanism
In multicellular organisms that require oxygen, such as human beings, anaerobic respiration can act as a backup when cellular oxygen is depleted. When muscle cells use up oxygen faster than it can be replenished, the cells start to perform anaerobic respiration in order to keep muscles moving, which can be important in an emergency situation.
Anaerobic respiration is more rapid than aerobic respiration.
Range of Habitat
Anaerobic metabolism allows microbes to inhabit low-oxygen or oxygen-free environments which allows them to exploit an otherwise empty habitat. Fermentation is an oxygen-free process and many useful microbes, such as yeast, are anaerobes. Anaerobes are also important decomposers. Their ability to decompose waste and produce combustible gas as a byproduct can be harnessed for a source of renewable energy.
- "Molecular Biology of The Cell"; Alberts et al; 1994
- Cliffs Notes: "Muscle Contraction"
- On-Line Biology Book: "Cellular Metabolism and Fermentation"
- Dictionary.com: "Lactic Acid"
- Renewable Energy Technologies: "Anaerobic Digesters"