Check here for the definition of respiration.

Anaerobic respiration

The respiration which occurs in the absence of oxygen and the organic food materials is incompletely oxidized into ethyl alcohol and CO₂ with a little amount of energy is called anaerobic respiration. It occurs in the cytoplasm of a cell. Such types of respiration occur in many tissues of higher plants, seeds, in storage, fleshy fruits, and muscles of animals. This process of incomplete oxidation is known as fermentation in the case of bacteria and fungi.

C₆H₁₂O₆ →CO₂ + C₂H₅OH + 50kcal

Mechanism of Anaerobic respiration

Anaerobic respiration involves glycolysis in which one molecule of glucose (GC) is degraded into two molecules of pyruvic acid (3C). pyruvic acid acts as H- acceptor. During the metabolic pathways, the end product of anaerobic respiration is either ethanol and carbon dioxide or lactic acid and not water.

1. Alcoholic fermentation

This process is involved in the brewing industry for producing beverages like beer, rum, whiskey, etc. It is done by brewing yeasts. It involves the following steps:

1. Decarboxylation of pyruvic acid in the presence of enzyme pyruvate decarboxylase. co-enzyme thiamine pyrophosphates and ZN⁺⁺ as a cofactor. It produces acetaldehyde.
   
   
2. Acetaldehyde accepts 2H atoms for NADH₂ in the presence of enzyme ethanol dehydrogenase and changes into ethanol.
   
   
3. Ethanol is lost so a large amount of energy goes to waste.
   
   
4. Accumulation of alcohol formed by fermentation in a culture of yeast cells stops the multiplication of yeast cells and may even lead to the death of cells.

Alcohol fermentation is also used in the baking industry in which CO₂ produced causes the doughing of wheat flour. It occurs in the presence of baking yeast.