What process generates ATP from glucose without the use of an electron transport chain?

The process that generates ATP from glucose without utilizing an electron transport chain is fermentation. This process occurs in the absence of oxygen and allows cells to produce ATP through substrate-level phosphorylation. During fermentation, glucose undergoes glycolysis to produce pyruvate, and then pyruvate is converted into various byproducts, such as ethanol or lactic acid, depending on the type of fermentation occurring. While glycolysis itself produces a small amount of ATP, fermentation serves as a subsequent stage to continue ATP production in an anaerobic environment.

Cellular respiration, on the other hand, typically involves an electron transport chain and requires oxygen for efficient ATP production alongside the Krebs cycle. Photosynthesis is the process by which plants convert light energy into chemical energy but does not involve direct ATP generation from glucose; rather, it produces glucose using carbon dioxide and water. Glycolysis is the initial step in both aerobic and anaerobic respiration, but it does not occur in isolation for ATP production without the electron transport system in aerobic conditions. Therefore, fermentation is the correct answer as it specifically addresses ATP generation in anaerobic conditions without the electron transport chain.