The breakdown of glucose by enzymes, releasing energy (ATP) and pyruvic acid is known as which process?

• A. Glycolysis
• B. Fermentation
• C. Krebs Cycle
• D. Electron Transport Chain

Answer: (A)

Glycolysis is the enzymatic breakdown of a glucose molecule into two pyruvate molecules, releasing energy in the process. It happens in the cytoplasm and does not require oxygen, so it can occur under both aerobic and anaerobic conditions. The pathway yields a net gain of 2 ATP through substrate-level phosphorylation and produces 2 NADH, with glucose ending as two pyruvate molecules. If oxygen is present, these pyruvate molecules can enter mitochondria to be further processed in the Krebs cycle; if not, cells can convert pyruvate to lactate or ethanol to regenerate NAD+ so glycolysis can continue. The other options refer to later stages of respiration (Krebs cycle uses acetyl-CoA derived from pyruvate; the electron transport chain relies on NADH and FADH2 to generate most ATP; fermentation occurs after glycolysis to recycle NAD+ without producing additional ATP beyond glycolysis).