Fermentation
Explanation
The metabolic conversion of carbohydrates (sugars) into alcohol, acids, or gases by microorganisms under anaerobic conditions is a fundamental biochemical process used extensively in industrial applications.
Option Analysis
- Pasteurisation is Incorrect: Pasteurisation is a process of heating liquids or foods to a specific temperature for a set period to kill pathogenic bacteria and reduce spoilage. It does not involve the conversion of sugar to alcohol.
- Nitrogen fixation is Incorrect: Nitrogen fixation is the process by which atmospheric nitrogen ($N_2$) is converted into ammonia ($NH_3$) or related nitrogenous compounds by certain bacteria (e.g., Rhizobium, Azotobacter). It is crucial for the nitrogen cycle, not alcohol production.
- Fermentation is Correct: Fermentation is the metabolic process where microorganisms, such as yeast (e.g., Saccharomyces cerevisiae), convert sugars (glucose, fructose, sucrose) into cellular energy, producing ethanol and carbon dioxide as by-products in the absence of oxygen. This process is the basis of the brewing and wine-making industries.
- Putrefaction is Incorrect: Putrefaction refers to the anaerobic decomposition of proteins by bacteria and fungi, resulting in the breakdown of tissues and the release of foul-smelling amines. It is distinct from the fermentation of carbohydrates.
Key Takeaway: Fermentation is the anaerobic breakdown of glucose by microbes like yeast to produce ethanol and carbon dioxide, serving as the primary method for industrial alcohol production.