Difference Between Fermentation and Anaerobic Respiration

Main Difference – Fermentation vs Anaerobic Respiration

Fermentation and anaerobic respiration are two types of cellular respiration mechanisms that are used to produce ATP for the functioning of the cell. Both fermentation and anaerobic respiration occur in the absence of oxygen. They use hexose sugars as the substrate. Hexose sugars first undergo glycolysis. The main difference between fermentation and anaerobic respiration is that fermentation does not undergo citric acid cycle (Krebs cycle) and electron transport chain whereas anaerobic respiration undergoes citric acid cycle and electron transport chain.

Key Areas Covered

1. What is Fermentation
      – Definition, Process, Application
2. What is Anaerobic Respiration
      – Definition, Process
3. What are the Similarities Between Fermentation and Anaerobic Respiration
      – Outline of Common Features
4. What is the Difference Between Fermentation and Anaerobic Respiration
      – Comparison of Key Differences

Key terms: Adenosine Triphosphate (ATP), Anaerobic Respiration, Citric Acid Cycle, Electron Transport Chain, Ethanol Fermentation, Fermentation, Glucose, Glycolysis, Lactic Acid Fermentation

What is Fermentation

Fermentation refers to any group of chemical reactions induced by microorganisms to convert sugars into carbon dioxide and ethanol. The sugars first undergo glycolysis. During glycolysis, the hexose sugar glucose is broken down into two pyruvate molecules. The pyruvate is a three-carbon compound. Glycolysis utilizes two ATP molecules while producing four ATP molecules from the energy released from glucose. The pyruvate is oxidized to ethanol or lactic acid. Based on the type of the end product, fermentation is categorized into two processes as ethanol fermentation and lactic acid fermentation, respectively. Yeast and some bacterial species perform fermentation. Ethanol fermentation is used to produce beer, bread, and wine. The net chemical equation for ethanol fermentation is shown below.

C₆H₁₂O₆ (Glucose) → 2 C₂H₅OH (Ethanol) + 2 CO₂ (Carbon dioxide)

Figure 1: Ethanol Fermentation

The lactic acid fermentation occurs in animal muscles and tissues when tissues require more energy. In the yogurt production, the lactic acid fermentation is used to produce lactic acid from lactose. The net chemical reaction for the production of lactic acid from glucose is shown below.

C₆H₁₂O₆ (Glucose) → 2 CH₃CHOHCOOH (Lactic acid)

What is Anaerobic Respiration

Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen. It occurs in the same way as aerobic respiration. Anaerobic respiration begins with glycolysis like the fermentation process, but it does not stop from glycolysis as fermentation does. After the production of the acetyl coenzyme A, anaerobic respiration continues the citric acid cycle as well as the electron transport chain.

Figure 2: Methanogenic Bacteria

The final electron acceptor is not the molecular oxygen as in aerobic respiration. Different types of organisms use different types of final electron acceptors. These can be sulfate ions, nitrate ions or carbon dioxide. Methanogenic bacteria are one such type of organisms that use carbon dioxide as the final electron acceptor in the absence of oxygen. They produce methane gas as a byproduct.  Some methanogenic bacteria are shown in figure 2. 

Similarities Between Fermentation and Anaerobic Respiration

• Both fermentation and anaerobic respiration occur in the absence of oxygen to produce energy.
• The respiratory substrate of both fermentation and anaerobic respiration are hexose sugars.
• Both fermentation and anaerobic respiration undergo glycolysis.
• The end products of both fermentation and anaerobic respiration are carbon dioxide and ethanol.
• The pyruvic acid and the acetylcholine are intermediates of both fermentation and anaerobic respiration.
• Both fermentation and anaerobic respiration are driven by enzymes.
• The rate of the sugar breakdown by both fermentation and anaerobic respiration increases in the presence of inorganic phosphates.

Difference Between Fermentation and Anaerobic Respiration

Definition

Fermentation: Fermentation refers to any group of chemical reactions induced by microorganisms to convert sugars into carbon dioxide and ethanol.

Anaerobic Respiration: Anaerobic respiration refers to a type of cellular respiration that occurs in the absence of oxygen.

Intracellular/Extracellular

Fermentation: Fermentation is an extracellular process.

Anaerobic Respiration: Anaerobic respiration is an intracellular process.

Oxygen

Fermentation: Fermentation is induced by low oxygen concentrations.

Anaerobic Respiration: Anaerobic respiration occurs in the absence of oxygen.

After glycolysis

Total ATP Production

Fermentation: The total ATP production is four in fermentation.

Anaerobic Respiration: The total production of ATP in anaerobic respiration is 38.

In vitro

Fermentation: The enzymes extracted from the fermenting cells can process the reaction in an extracellular medium.

Anaerobic Respiration: The enzymes extracted from the cells cannot process the anaerobic respiration in an extracellular medium.

Conclusion

Fermentation and anaerobic respiration are two types of respiration mechanisms that occur in the absence of oxygen. Both fermentation and anaerobic respiration occur through glycolysis. In fermentation, the pyruvate molecules are converted into lactic acid or ethanol. In anaerobic respiration, the citric acid cycle and the electron transport chain are also carried out. But, the final electron acceptor is an inorganic molecule such as sulfate, nitrate or carbon dioxide. The main difference between fermentation and anaerobic respiration is the mechanism of each type of respiration. 

Reference:

1.“ Fermentation.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 27 June 2017, Available here. Accessed 30 Sept. 2017.
2.“Anaerobic respiration.” Wikipedia, Wikimedia Foundation, 27 Sept. 2017, Available here. Accessed 30 Sept. 2017.

Image Courtesy:

1. “Fermentation alcoolique” By Pancrat – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Phylogenetic tree methanogen” By Crion – File:メタン菌の系統関係.png (CC BY-SA 3.0) via Commons Wikimedia