Compare the amount of ATP that is produced in fermentation, glycolysis and the Krebs cycle
The correct answer and explanation is:
Fermentation, glycolysis, and the Krebs cycle all contribute to ATP production, but they do so in different ways and to varying extents.
Glycolysis occurs in the cytoplasm and is the first step in both aerobic and anaerobic respiration. It involves the breakdown of one molecule of glucose (6 carbon atoms) into two molecules of pyruvate (3 carbon atoms each). During this process, a net gain of 2 ATP molecules is produced. Additionally, 2 molecules of NADH are formed, which can later be used in aerobic respiration to generate more ATP. However, glycolysis alone does not produce a large amount of ATP.
Fermentation is an anaerobic process that occurs when oxygen is unavailable. It begins with glycolysis and results in the production of 2 ATP molecules, but since fermentation doesn’t involve the electron transport chain, no additional ATP is generated. The pyruvate produced from glycolysis is converted into either lactate (in animals) or ethanol and carbon dioxide (in yeast and some bacteria). While fermentation provides a quick source of energy, it is much less efficient compared to aerobic respiration.
The Krebs cycle occurs in the mitochondria and is part of aerobic respiration. It begins with acetyl-CoA (derived from pyruvate) combining with oxaloacetate to form citric acid. Through a series of reactions, the Krebs cycle produces 2 ATP molecules per glucose molecule (since each glucose molecule is split into two pyruvate molecules, which enter the cycle). Additionally, the Krebs cycle produces high-energy electron carriers, NADH and FADH2, which are crucial for ATP production in the next step, oxidative phosphorylation. Overall, the Krebs cycle is responsible for a significant portion of the ATP produced in aerobic respiration.
In summary, glycolysis produces 2 ATP, fermentation produces an additional 2 ATP (but is less efficient), and the Krebs cycle contributes 2 ATP, along with electron carriers that help produce much more ATP in oxidative phosphorylation. Aerobic respiration, which includes glycolysis, the Krebs cycle, and oxidative phosphorylation, is much more efficient than fermentation.