Which process produces a net yield of only 2 ATP, indicating inefficiency?

• A. Aerobic respiration
• B. Fermentation
• C. Krebs cycle
• D. Glycolysis

Answer: (B)

Fermentation is the process that produces a net yield of only 2 ATP, which highlights its inefficiency compared to other metabolic pathways. During fermentation, glucose is primarily converted into lactate or ethanol and carbon dioxide depending on the type of organism and conditions. This anaerobic process is less efficient because it does not utilize the electron transport chain, which is prominent in aerobic respiration and significantly increases ATP yield.

In contrast, aerobic respiration, including the Krebs cycle and electron transport chain, can produce much more ATP per glucose molecule, typically yielding around 30-32 ATP. Glycolysis, although it generates only 2 ATP as well, is the first step in both fermentation and aerobic respiration; thus, it itself does not define the inefficiency of yield. Essentially, while glycolysis operates in both aerobic and anaerobic contexts, fermentation is distinct in its inability to utilize oxygen for a more efficient ATP production pathway. This is why fermentation is characterized by a net yield of 2 ATP and is considered less efficient relative to aerobic processes.