Question

Give the chemical reaction taking place in anaerobic respiration in yeast.

Answer 1

Anaerobic respiration which is the opposite of aerobic respiration is a metabolic process of energy production without oxygen. It allows an organism to produce usable energy without the involvement of oxygen. The final products of anaerobic respiration are different from aerobic in addition to fermentation products.

Complete answer: A yeast is single-celled fungi species extensively used in the commercial process such as brewing and bread-making. Yeast normally respires through aerobic respiration. But when it is devoid of oxygen, it undergoes an anaerobic mode of respiration. This ability of yeast makes the most suitable organism for the fermentation process. In fermentors, the yeast is provided with complex sugars or polysaccharides, which yeast cells use as a substrate. Glucose $({{C}_{6}}{{H}_{12}}{{O}_{6}})$ is one of the most common substrates supplied to yeasts for anaerobic respiration. Once glucose is supplied, the yeast cells break down into ethanol $({{C}_{2}}{{H}_{5}}OH)$ and energy, with the liberation of carbon dioxide $(C{{O}_{2}})$. It is a decomposition reaction and the energy produced is less than aerobic respiration. Similar to aerobic respiration, the metabolic respiration in anaerobic respiration continues until glycolysis. The glucose is converted into two pyruvate molecules and yields two molecules of ATP (Adenosine Triphosphate) which is the energy molecule of all organisms. Now, instead of further processing of pyruvate as in aerobic respiration, the pyruvate is converted directly into ethanol in the anaerobic mode. Carbon dioxide is released as a by-product in this process.
So, the above reaction can be represented as:
${{C}_{6}}{{H}_{12}}{{O}_{6}}\to {{C}_{2}}{{H}_{5}}OH+~C{{O}_{2}}+2ATP~~~$

Note: In humans, muscle tissues also respire anaerobically during extensive exercise as blood cannot reach these tissues fast. When the body is not able to take up enough oxygen for aerobic respiration, muscle tissues start respiration without oxygen. Glucose is degraded and broken down into lactic acid and energy. Accumulation of lactic acid in muscles may lead to muscle cramps.