Why is less energy produced during anaerobic respiration than in aerobic respiration?
The correct answer and explanation is:
In anaerobic respiration, less energy is produced than in aerobic respiration due to the difference in how glucose is processed. In aerobic respiration, glucose undergoes a complete oxidation process in the presence of oxygen, whereas in anaerobic respiration, oxygen is not available, and the process is less efficient.
In aerobic respiration, glucose is fully broken down in three main stages: glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation. During glycolysis, glucose is split into two molecules of pyruvate, and a small amount of ATP is generated. The pyruvate then enters the mitochondria, where it is further oxidized in the citric acid cycle, producing electron carriers like NADH and FADH2. These carriers then donate electrons to the electron transport chain, where oxygen acts as the final electron acceptor. This process creates a large proton gradient, driving the production of a significant amount of ATP through oxidative phosphorylation. The overall result is the production of up to 36 or 38 ATP molecules per glucose molecule.
In contrast, during anaerobic respiration, oxygen is absent, so cells rely on a much simpler process. After glycolysis, the pyruvate produced is converted into either lactic acid (in animals) or ethanol and carbon dioxide (in yeast), depending on the organism. However, this conversion of pyruvate does not generate any additional energy, and only 2 ATP molecules are produced from the initial glycolysis step. Without the electron transport chain and oxidative phosphorylation, the energy yield is significantly lower.
Thus, the key reason less energy is produced in anaerobic respiration is that it only relies on glycolysis, which provides much less ATP compared to the complete oxidation of glucose in the presence of oxygen.