In which condition does fermentation occur?

Fermentation occurs in the absence of oxygen, making it a crucial metabolic process for many organisms, particularly under anaerobic conditions. When oxygen is limited or unavailable, cells switch to fermentation to generate energy. This process allows organisms to convert carbohydrates, such as sugars, into energy, producing byproducts like alcohol or lactic acid depending on the specific type of fermentation.

In anaerobic environments, such as deep water sediments or within the gastrointestinal tracts of animals, fermentation is a vital means of energy production. It enables microbes and certain eukaryotic organisms to survive and thrive where aerobic respiration cannot take place. This capability is essential in various ecological niches and contributes significantly to the overall carbon cycle and energy flows in ecosystems.