Respiration occurs in two ways, aerobic respiration that uses oxygen to function and anaerobic respiration which functions without oxygen. Anaerobic respiration start by breaking down the molecules of glucose and produces pyruvic acid. This acid then ferments and produces ATP, which is used by the cells for producing energy. One good thing is that human beings are able to perform both types of respiration.

There are some plants and animals, which can use anaerobic respiration also, but only for a short period of time. This is possible especially during running or sprinting when the muscles use anaerobic respiration. Whenever we perform intense physical exercises, our muscles use anaerobic respiration and produces lactic acid. The production of lactic acid and its buildup is the main reason why our muscles become weak and pain after exertion.

The anaerobic respiration is the oldest method of cellular respiration. Many single celled primitive organisms, which inhabit in places and environments lacking oxygen, such as the muddy bottom of a river, use this form of respiration for living.

This type of respiration primarily works by fermentation, which is also known as glycolysis. In this process, one glucose molecule is divided into two pyruvic acid molecules and acquires two molecules of ATP.  Then these ATP’s are used for splitting a molecule of glucose into two chains, each consisting of three numbers of a carbon atom. Both chains have one-phosphate groups at their end. Continuing the process, a different phosphate group gets itself attached to each of the three carbon chains. As a result, both of the phosphate groups on every chain are divided equally amongst the two molecules, which are known as ADP (Adenosine Diphosphate) and then turn into ATP.

During anaerobic respiration carbohydrates are partly oxidized and chemical energy is released without the requirement of oxygen. Some yeasts and bacteria and some muscle tissue also uses anaerobic respiration. Fermentation of the alcohol, which produces ethanol, is a perfect example of anaerobic respiration. This is the basis of the production of alcohol. The main purpose of anaerobic respiration is to produce ATP (Adenosine Triphosphate), which a cell uses for energy purposes.

Though this process of respiration is less efficient in producing energy, because it produces only two ATP molecules in comparison to 38 molecules produced during aerobic respiration. Aerobic respiration is in reality a faster process. This process is also used in making of breads, where the anaerobic respiration of the yeasts helps the bread to rise.

The anaerobic respiration conducted by the cells give rise to lactic acid, a chemical that actually helps in burning our muscles, if we do physical labor for a short time. Through this process of respiration, certain microorganisms throw out ethyl alcohol and carbon dioxide, which are actually waste products.

This form of respiration is very primitive and had started from the time or period when oxygen was missing in our atmosphere. Many living organisms have successfully adapted to anaerobic form of respiration to survive especially in environments and habitats that are not suitable for life due to insufficient oxygen or in the places that are totally lacking in it.

All living creatures, be it man or the smallest bacteria have one function in common, which is known as respiration. During respiration, two important functions are performed in living things. In the first, electrons that were generated during the catabolism are disposed off and in the second, ATP (also known as adenosine tri-phosphate) is produced. Respiration is conducted from the cell membranes through the prokaryotes, which is found inside the mitochondria.

There are two types of respiration (i) aerobic respiration and (ii) anaerobic respiration. While aerobic respiration is a process that requires oxygen, but in anaerobic respiration, oxygen is not required. Therefore aerobic and anaerobic respiration differs in terms of the amount of energy that is produced.

In aerobic respiration, oxygen is always required. During the process of aerobic respiration, the molecules of food are broken down to obtain energy. Oxygen is present at the end point of the electron acceptor. The molecules of fuel that are generally used by the cells of the body during the process of the respiration are composed of glucose, fatty acids and amino acids. In other words, when there is respiration through the aerobic process, Glucose together with Oxygen produces Energy, Carbon Dioxide and Water.

A lot of energy is produced during aerobic respiration, which may be as high as 38 ATP molecules for every glucose molecule. This means that during aerobic respiration only one molecule of glucose will produce about thirty-eight energy units.

In plain language, anaerobic means where there is no air and thus anaerobic respiration is a term used for the respiration that occurs without the use of oxygen. In this process, the molecules carry oxidation, when oxygen is absent. This results in the production if energy or ATP. This type of respiration is also equivalent to fermentation when energy production path (Glycolytic pathway) is functioning in one cell. There are two processes of this respiration (i) alcoholic fermentation, where the Glucose gets broken down and produces Energy (ATP), Ethanol and Carbon Dioxide as well as (ii) Lactate fermentation where Glucose breaks itself into Energy and Lactic Acid.

Anaerobic respiration produces less energy when compared with the process of aerobic respiration. This can be best illustrated with the fact that during the anaerobic respiration only two molecules of ATP are yielded for one glucose molecule

Anaerobic respiration produces less energy in comparison to aerobic respiration. When the anaerobic respiration (alcoholic fermentation) as at one above functions, only two molecules of ATP are given out for one glucose molecule, while for lactate fermentation as at two above, 2 ATP molecules are given out for each glucose molecule used during the process. Thus, during anaerobic respiration, only one molecule of glucose is broken down to obtain only 2 ATP molecule.

Generally anaerobic respiration is always used by the primitive living organisms, which live in places where oxygen is missing, like muddy bottom of a river. In such places, the organism survives without depending to a large extent on oxygen. These habitats are known as anoxic.