What type of respiration occurs in the absence of oxygen?

Fermentation is the correct answer because it describes a metabolic process that occurs when cells generate energy in the absence of oxygen. During fermentation, glucose is partially broken down to produce energy, resulting in byproducts such as ethanol or lactic acid, depending on the type of organism. This process allows cells to continue producing ATP (adenosine triphosphate) when oxygen is limited or unavailable, making it an essential pathway for anaerobic conditions.

Aerobic respiration requires oxygen to fully oxidize glucose and produce energy, while cellular respiration broadly encompasses both aerobic and anaerobic processes. Photosynthesis, on the other hand, is a process used by plants and some microorganisms to convert light energy into chemical energy, and it specifically requires light rather than being related to the presence or absence of oxygen in terms of energy production.