Why does anaerobic respiration transfer less energy than aerobic respiration?

Anaerobic respiration transfers less energy than aerobic respiration primarily because glucose is not fully oxidized during the process. In aerobic respiration, glucose undergoes complete oxidation in the presence of oxygen, resulting in the production of carbon dioxide and water, along with a significant yield of ATP (adenosine triphosphate) — the energy currency of the cell.

However, in anaerobic respiration, which occurs when oxygen is scarce or absent, glucose is only partially broken down. This partial oxidation leads to the production of byproducts such as lactic acid in animals or ethanol and carbon dioxide in yeast, along with a smaller amount of ATP. Consequently, since anaerobic respiration does not fully convert glucose into carbon dioxide and water, it releases much less energy overall compared to the complete process in aerobic respiration.

This understanding highlights the importance of oxygen in maximizing energy yield from glucose, making it crucial for many organisms that rely on aerobic pathways for their energy needs.