Difference Between Fermentation and Respiration

Main Difference – Fermentation vs Respiration

Fermentation and respiration are two types of cellular processes, involved in the breaking down of glucose in the cell. Both fermentation and respiration are catabolic processes, generating energy in the form of ATP. The main difference between fermentation and respiration is that during fermentation, NADH is not used in the oxidative phosphorylation in order to generate ATP whereas, during respiration, NADH is used in the oxidative phosphorylation in order to generate three ATPs per NADH.

This article looks at, 

1. What is Fermentation
      – Characteristics, Process
2. What is Respiration
      – Characteristics, Process
3. What is the difference between Fermentation and Respiration

Difference Between Fermentation and Respiration - Comparison Summary

What is Fermentation

Fermentation is the chemical breakdown of organic substrates like glucose by microorganisms like bacteria and yeast, typically giving off effervescence and heat. It occurs in microorganisms like some bacteria, yeast, and parasitic worms. Fermentation is localized in the cytoplasm of those organisms’ cells. The net yield of fermentation is only 2 ATPs. The process of fermentation occurs in two steps: glycolysis and partial oxidization of pyruvate.

There are two types of fermentation known as ethanol fermentation and lactic acid fermentation. Ethanol fermentation occurs in yeast in the absence of oxygen. Hence, they are called facultative anaerobes. Lactic acid fermentation occurs in bacteria. In the absence of oxygen, animals also produce lactic acid mainly in their muscles. Lactic acid is toxic to tissues. Glycolysis is same for both fermentations. During glycolysis, glucose is broken down into two pyruvate molecules, generating 2 ATPs as the net gain. Other than that, two molecules of NADH are formed by obtaining electrons from glyceraldehyde-3-phosphate. During ethanol fermentation, pyruvate is decarboxylated into acetaldehyde by removing carbon dioxide. Acetaldehyde is converted into ethanol by using the hydrogen atoms of the NADH. The effervescence occurs due to the releasing of carbon dioxide gas into the medium by the cells in the medium. During lactic acid fermentation, pyruvate is converted into lactic acid, which is then oxidized into lactate. The overall chemical reaction for ethanol fermentation and lactic acid fermentation are given below.

Ethanol Fermentation:

C6H12O6  →  2C2H5OH  +  2CO2  + 2ATP

Lactic Acid Fermentation:                                     

C6H12O6  →  2C3H6O3  +  2ATP

Main Difference - Fermentation vs Respiration

Figure 1: Ethanol and lactic acid fermentation

What is Respiration

Respiration is the set of chemical reactions involved in the production of energy by completely oxidizing food. It releases carbon dioxide and water as by-products. Respiration is the most abundant and most efficient process among the processes of energy production. It occurs in higher plants and animals who are using complex cellular processes with high energy consumptions. During respiration, 36 ATPs are produced. The whole process occurs in the cytoplasm and mitochondria.

Respiration occurs through three steps: glycolysis, citric acid cycle and electron transport chain. Glycolysis occurs in the cytoplasm of the cell in the same way it occurs during fermentation. The two pyruvate molecules produced in the glycolysis is transferred into the mitochondrial matrix. They release two carbon dioxide molecules, one from each and become acetyl-CoA during oxidative decarboxylation. This acetyl-CoA enters into the citric acid cycle, which is also known as Krebs cycle. During the citric acid cycle, a single glucose molecule is completely oxidized into six carbon dioxide molecules, generating 2 GTPs, 6 NADH and 2 FADH2. These NADH and FADH2 are combined with oxygen, generating ATP during oxidative phosphorylation, which occurs in the inner mitochondrial membrane. During the oxidative phosphorylation, electrons in NADH and FADH2 are transferred through a series of electron carriers called electron transport chain. The net yield of ATPs is thirty six in respiration. The overall chemical reaction is shown below.   

Respiration:

C6H12O6  +  6O2  →  6CO2  +  6H2O  +  36ATP

Difference Between Fermentation and Respiration

Figure 2: Respiration

Difference Between Fermentation and Respiration

Definition

Fermentation: Fermentation is the chemical breakdown of an organic substrate like glucose by microorganisms like bacteria and yeast, typically giving off effervescence and heat.

Respiration: Respiration is the set of chemical reactions involved in the production of energy by completely oxidizing food. It releases carbon dioxide and water as by-products.

Oxygen

Fermentation: Oxygen is not required for fermentation.

Respiration: Oxygen is required for respiration.

Water

Fermentation: No water is produced during fermentation.

Respiration: Water is produced as a by-product during respiration.

Occurrence

Fermentation: Fermentation occurs in the cytoplasm.

Respiration: Respiration occurs in cytoplasm and mitochondria.

Net yield of ATP

Fermentation: Fermentation generates only two ATPs by the breaking down of a single glucose molecule.

Respiration: Respiration generates 36 ATPs by the breaking down of a single glucose molecule.

Substrate Oxidation

Fermentation: The substrate, glucose is not completely broken down during fermentation.

Respiration: The substrate, glucose is completely broken down during respiration.

Types

Fermentation: Ethanol fermentation and lactic acid fermentation are the two types of fermentations found in organisms.

Respiration:  Aerobic and anaerobic respiration are two types of respiration found in organisms.

Final Electron Acceptor

Fermentation: Final electron acceptor in fermentation is an organic molecule, usually acetaldehyde in ethanol fermentation and pyruvate in lactic acid fermentation.

Respiration: Final electron acceptor is mainly oxygen.

End Products

Fermentation: Ethanol fermentation generates ethanol and carbon dioxide. Lactic acid fermentation generates lactic acid as the end product.

Respiration: Respiration generates inorganic end products, carbon dioxide, and water.

NAD+ Regeneration

Fermentation: No ATP is produced during the regeneration of NAD+ in fermentation.

Respiration: Three ATPs are generated during the regeneration of NAD+ in respiration.

Oxidative Phosphorylation

Fermentation: No oxidative phosphorylation occurs during fermentation.

Respiration: In respiration, ATPs are generated from NADH and FADH2 through oxidative phosphorylation.

Type of Organism

Fermentation: Fermentation is usually found in microorganisms like yeast.

Respiration: Respiration is found in higher organisms.

Contribution

Fermentation: Fermentation has a less contribution in the production of energy for the cellular processes on earth.

Respiration: Respiration has the highest contribution in the production of energy for the cellular processes on earth.

Conclusion

Fermentation and respiration are two processes involved in the catabolism of organic substrates which are used as food during the production of energy required by the cellular processes. During fermentation and respiration, the potential energy stored in organic molecules are converted into kinetic chemical energy in the form of ATP. Both processes begin with glycolysis, resulting in two pyruvate molecules. Glycolysis occurs in the cytoplasm of all cells on earth. Oxygen is not involved in the glycolysis. But in the presence of oxygen, pyruvate in the cytoplasm enters into the mitochondrial matrix in order to undergo citric acid cycle, which completely oxidizes pyruvate. This complete oxidization only occurs in respiration. NADH and FADH2 are also produced by the citric acid cycle. They are reduced by oxidative phosphorylation in the inner membrane of the mitochondria. In contrast, fermentation occurs in the absence of oxygen, incompletely oxidizing pyruvate either into ethanol or lactate. During ethanol fermentation, pyruvate is converted into acetaldehyde, which is then converted into ethanol. The NADH produced in the glycolysis of fermentation, donates its electrons to acetaldehyde while regeneration. Therefore, the main difference between fermentation and respiration is the ability to produce ATP during the regeneration process of NAD+.

Reference:
1. Cooper, Geoffrey M. “Metabolic Energy.” The Cell: A Molecular Approach. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 07 Apr. 2017.
2. Jurtshuk, Peter, and Jr. “Bacterial Metabolism.” Medical Microbiology. 4th edition. U.S. National Library of Medicine, 01 Jan. 1996. Web. 07 Apr. 2017.

Image Courtesy:
1. “Heterofermentative Milchsäuregärung” By Yikrazuul – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “By Darekk2 – Own work (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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