Which of the following processes releases energy in the absence of oxygen?

The process that releases energy in the absence of oxygen is fermentation. Fermentation is an anaerobic process, meaning it occurs without the presence of oxygen. During fermentation, organisms such as yeast and certain bacteria convert sugars into energy, producing byproducts like alcohol or lactic acid, depending on the type of organism and the substrates used. This process is essential for survival in environments where oxygen is scarce, allowing cells to continue generating ATP (adenosine triphosphate), the energy currency of the cell.

Aerobic respiration, on the other hand, requires oxygen to efficiently produce energy through the complete breakdown of glucose. Cellular respiration encompasses both aerobic and anaerobic processes, but it is the aerobic pathway that maximizes energy output. Photosynthesis, which occurs in plants, uses sunlight to convert carbon dioxide and water into glucose and oxygen, and is not a process associated with energy release in the absence of oxygen. Thus, fermentation is uniquely suited for energy production without oxygen, making it the correct answer.