Aerobic Respiration and Anaerobic Respiration – Diagrams, Definition and Differences

Aerobic Respiration vs Anaerobic Respiration

Respiration is the most important metabolic reaction that is necessary for the survival of an organism. No organism can survive if it is not able to perform respiration. Respiration is the process of breaking down complex organic compounds and producing energy in the form of adenosine triphosphate (ATP).

The two common ways by which all organisms respire are Aerobic Respiration and Anaerobic Respiration. In this article, we will go through a basic introduction of both the processes and a brief comparison between the two.

Aerobic Respiration

Definition

• Aerobic Respiration is the process of respiration in which oxygen is the final electron acceptor in the electron transport chain. 
• It occurs in organisms when they have a free and excess supply of oxygen.
• It is the common process carried out in all types of organisms except some ancient bacteria and archaea. 

Steps

• Aerobic Respiration is a complex and continuous process but for convenience, it is divided into three basic steps.
• The first step is Glycolysis, which takes place in the cytosol of the cell.
• The second step is Krebs cycle, it takes place in the Mitochondria.
• The third step is Electron Transport Chain, it takes place in the Mitochondrial membranes.

Types

• This type of respiration is one of its kind and has the same mechanism in all organisms. It has no further types.

Net ATP yield

• The main product of Aerobic respiration is Energy. This energy is produced in the form of ATP. In each cycle, a total of 38 ATP are produced
• Glycolysis yields 2 ATP in each cycle.
• Krebs cycle yields 2 ATP in each cycle.
• Electron Transport Chain yields 34 ATP molecules in each cycle.

Conditions of Occurrence

• There are two limiting factors for aerobic respiration. These are free oxygen and the capability of the organism to perform aerobic respiration. 
• Free oxygen means that there should be an excessive and constant supply of oxygen in the environment to perform aerobic respiration.
• Some organisms are not capable of performing aerobic respiration e.g. some archaea and bacteria. Such organisms take energy in other ways, for example, anaerobic respiration.

Respiration in Humans

• The mode of respiration in humans, as well as all higher animals, is aerobic respiration.
• The process starts with the breakdown of glucose into two molecules of pyruvic acid in the cytoplasm of the cell.
• Glycolysis is followed by the Krebs cycle and Electron Transport Chain.

Anaerobic Respiration

Definition

• Anaerobic Respiration is the process of respiration that takes place in the absence of oxygen, or in the limited supply of oxygen.
• The final electron acceptor in this type of respiration is not oxygen, but some inorganic ion.
• This process is carried out by some primitive organisms. It is also carried out in the human body when we exercise.

Steps

• The first step of anaerobic respiration is the same as aerobic respiration i.e. glycolysis. It is because glycolysis does not require oxygen.
• The further steps of anaerobic respiration depend upon the type of anaerobic respiration being performed.

Net ATP yield

• The net ATP yield of anaerobic respiration is only 2 ATP.

Organisms Capable Of Anaerobic Respiration

The organisms capable of anaerobic respiration are mostly primitive bacteria and archaea which inhabited the planet when there was a limited supply of oxygen in the environment. Some of the examples include

• Archaea e.g. methanogens
• Bacteria e.g. Clostridium tetani
• Human body during excessive running and exercise.
• Several yeasts

Types of Anaerobic Respiration

• There are two types of anaerobic respiration based on the end-product of each reaction:
• It may be Alcoholic Fermentation or Lactic acid fermentation.
• Alcoholic fermentation takes place in anaerobic organisms such as some bacteria and yeasts.

Examples of Anaerobic Respiration

1. Lactic Acid Fermentation in the Human Body

• Lactic acid fermentation in the human body takes place when there is not enough oxygen intake.
• This happens during intense exercise and running.
• The glucose gets broken down into lactic acid and gets accumulated in the muscles.
• The reaction is as follows:  C₆H₁₂O₆  → C₃H₆O₃ + energy

2. Alcoholic Fermentation

• This type of fermentation happens in yeasts. 
• Yeast has the ability to convert glucose into pyruvic acid and then into ethyl alcohol and also releases carbon dioxide.
• This method can be used to brew ethyl alcohol.
• The reaction is as follows: C₆H₁₂O₆   →    C₂H₅OH + CO₂ + energy

3. Fermentation in Archaea

• Some types of archive i.e methanogens also respire anaerobically.
• The by-product of fermentation is methane.
• They produce alcohol i.e. methanol.
• The general reaction is given as C₆H₁₂O₆    →   CH₃OH + CO₂ + energy

4. Fermentation in Cheese

• Some bacteria use carbohydrates in cheese for fermentation.
• They convert carbohydrates into propionic acid and carbon dioxide.
• This type of fermentation is called propionic acid fermentation.
• The reaction is given as C12H22O11    →    C3H6O2 + CO2 + energy

Difference between Aerobic Respiration and Anaerobic Respiration

	Aerobic Respiration	Anaerobic Respiration
Definition	The type of respiration that takes place in the presence of oxygen.	The type of respiration that takes place in the absence or limited supply of oxygen.
Site of Occurrence	It takes place in the mitochondria and cytosol.	It takes place only in the cytosol.
Reactants Needed	Glucose and Oxygen are the necessary reactants for this process.	Glucose and any other inorganic electron acceptor are the reactants for these reactions.
Products formed	Carbon dioxide, water, and energy in the form of ATP are produced during the reaction.	Water, ATP and any reduced species which acted as electron acceptors are the final product of the reaction.
General Equation	C6H12O6 + 6O2 →  6CO2 + 6H2O + energy	C6H12O6 →C2H5OH + CO2 + energy
Production of Organic Acids	It does not produce any organic acids such as lactic acid and ethanol.	Anaerobic Respiration produces organic acids such as lactic acid and ethanol.
Completion of Reaction	Aerobic respiration is the complete oxidation of glucose in the presence of oxygen.	Anaerobic respiration is the incomplete oxidation of glucose in the limited supply of oxygen.
Krebs Cycle and Electron Transport Chain	Krebs cycle is a series of reactions that take place in the mitochondria and utilize oxygen to convert ADP into ATP along with CO2 as a by-product. Electron transport chain is a series of electron acceptors which transport electrons down the potential gradient and couple these redox reactions with the production of NADH. Both the reactions take place in aerobic respiration.	None of the  reactions take place in an anaerobic mode of respiration.
Net ATP yields	Net ATP yield refers to the difference between total ATP produced and total ATP utilized in the process. It is the ATP profit of the process.Aerobic respiration produces 36 ATP in total.	Anaerobic respiration produces only 2 ATP in total.
Profitable	It is more profitable for organisms as it produces more ATP.	It is less profitable as it produces just a minimal amount of ATP.
Time Taken	It takes longer to complete a single reaction of aerobic reaction as it requires complete oxidation of glucose.	Anaerobic respiration is a quick reaction and instantly provides energy in the form of ATP
Significance	It is the main source of ATP production in almost all living organisms.	It is the main source of ATP production in anaerobic organisms.
Early life	This method of respiration was not present in early organisms on earth.	Early life on earth consisted of organisms that could respire anaerobically.
Type of Organisms	It is found as a major reaction in all higher and more complex living organisms.	It is found in all primitive organisms.
The obligation of Organisms	Aerobic organisms can not live without oxygen as they can not perform respiration.	Anaerobic organisms such as anaerobic bacteria die in the presence of oxygen because oxygen superoxides are toxic for them and they do not have any enzymes to break down these oxides.
Example	Humans during normal breathing. All animals during normal breathing and aerobic bacteria	Anaerobic Bacteria, Archeae e.g. methanogens and Human body during running and exercise

Frequently Asked Questions

References

1. https://www.diffen.com/difference/Aerobic_Respiration_vs_Anaerobic_Respiration
2. https://microbenotes.com/aerobic-vs-anaerobic-respiration/
3. Molecular Biology of the Cell by Bruce Alberts
4. https://byjus.com/biology/aerobic-anaerobic-respiration/
5. https://study.com/academy/lesson/differences-between-aerobic-vs-anaerobic-respiration.html
6. https://www.diffen.com/difference/Aerobic_Respiration_vs_Anaerobic_Respiration