Under anaerobic conditions, two processes that take place are fermentation and anaerobic respiration.
Fermentation is a metabolic process where sugars are broken down without the use of oxygen, resulting in the production of energy in the form of ATP and byproducts such as alcohol (ethanol) or lactic acid.
Anaerobic respiration is a process that occurs in some organisms, including certain bacteria and archaea. It involves the breakdown of organic molecules in the absence of oxygen, producing energy through alternative electron acceptors like sulfate or nitrate.
These processes are essential for organisms that live in environments with low or no oxygen availability.