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What is Anaerobic Respiration?

What is Anaerobic Respiration?
Anaerobic respiration is a process in which organisms produce energy in absence of oxygen. This BiologyWise article tells you about all the steps of anaerobic respiration in detail.
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Did You Know?
  • Due to anaerobic respiration in some plants and yeast, ethanol is produced, which forms the base for consumable alcohol.
  • In baking, bread rises because of the anaerobic respiration of yeast and CO2.
Respiration is an important process of life. It is a biochemical pathway that releases energy from the chemical bonds in glucose, and in turn, this energy is used to carry out the other essential functions of life. Each and every living cell follows cellular respiration. Cellular respiration can be carried out by two different pathways. The cellular respiration that occurs in presence of oxygen is called aerobic respiration, and the one that occurs in absence of oxygen is anaerobic cellular respiration.

In prokaryotic cells, the cellular respiration steps are carried out within the cytoplasm and the inner surfaces of the cells. In case of eukaryotic cells, mitochondria is the site of energy production. The energy is produced in form of ATP (Adenosine Triphospahate).

Aerobic Cellular Respiration
Glucose → Glycolysis → TCA Cycle → Electron Transport Chain → ATP

In cellular respiration, the by-product is CO2. This metabolic waste binds with water and forms carbonic acid that is essential to maintain the pH of the blood. If CO2 is in excess, it will lower the pH. Therefore, the excess CO2 is removed from the body regularly. This was a brief description about aerobic respiration.

What is Anaerobic Respiration?
The anaerobic respiration definition states that it is the pathway where the glucose is broken down into molecules in the absence of oxygen to produce energy. The first step in all cellular respiration pathways is glycolysis that takes place without the presence of molecular oxygen. If there is oxygen in the cell, then it automatically turns to aerobic respiration with the help of tricarboxylic acid cycle (TCA). The TCA cycle helps in production of usable energy in the form of ATP that is higher in quantity than any anaerobic respiration process.

The anaerobic cellular respiration process is the sole cycle for production of energy for many anaerobic bacteria. Many eukaryotic cells also switch on their anaerobic respiration process in case the oxygen supply is low. The best example for this process in eukaryotic cells is the human muscles. Let us see this through the following example:

Anaerobic Respiration Process in Muscles
When we exercise, our body responds to the working muscles by supplying more oxygen. In presence of oxygen, the glucose is broken down into carbon dioxide and water. But when we follow extraneous activities, the oxygen level in the muscle tissue decreases. This is because the supply does not meet the demand. This low-level oxygen results in anaerobic respiration of the cells, and there is lactic acid buildup to provide the much-needed ATP molecules for cellular functions. This makes your muscles tired, and you may suffer from cramps.

Anaerobic Respiration Equation
In anaerobic respiration process, glycolysis, which is the first step, is an aerobic cellular respiration. This step yields two ATP molecules. The product of glycolysis is pyruvate that used in anaerobic respiration fermentation. This anaerobic respiration fermentation helps in production of ethanol and Nicotinamide Adenine Dinucleotide (NAD+) or for production of lactate and NAD+. The production of NAD+ is very necessary as glycolysis uses it, and if there is depletion of NAD+, it will lead to cell death. Anaerobic respiration process follows the Krebs cycle and occurs in the fluid of cytoplasm. The major energy yield of aerobic respiration takes place in the mitochondria. A lot of energy goes waste in the form of ethanol and lactate molecules as the cell cannot utilize them. Instead, they excrete these products as waste. Anaerobic respiration takes place in the form of two pathways, alcoholic fermentation and lactic acid fermentation. Below is the chemical equation for anaerobic respiration:

Anaerobic Respiration Formula
2ATP"+ C 6H 1206 Enzymes 2CH3CH2OH + 2CO2 + 4ATP

Anaerobic respiration is energetically less efficient than aerobic respiration. There are many enzymes and molecules that are involved in the anaerobic pathway.