Which process is primarily responsible for the production of ATP in glycolysis?

In glycolysis, substrate-level phosphorylation is the process responsible for the production of ATP. This occurs when a phosphate group is directly transferred from a phosphorylated intermediate to ADP, forming ATP. In glycolysis, this happens during specific steps where enzymes facilitate the transfer of a phosphate group to ADP, allowing for the generation of ATP without the involvement of electron transport chains or the need for an electrochemical gradient, which are required in processes like oxidative phosphorylation and chemiosmosis.

The advantage of substrate-level phosphorylation is that it can occur even in the absence of oxygen and does not rely on any membrane-bound processes, thus making it essential in anaerobic conditions. This ability to generate ATP directly from metabolic intermediates is a key feature of glycolysis, which is the first stage of cellular respiration, leading to further energy extraction in later stages.