Final answer:
Under anaerobic conditions, the conversion of glucose to pyruvate results in the formation of lactic acid. This process, known as fermentation, allows ATP production to continue when oxygen is limited. However, in the presence of oxygen, pyruvate is converted into acetyl CoA and enters the citric acid cycle for aerobic respiration.
Step-by-step explanation:
The pathway of glucose to pyruvate under anaerobic conditions leads to the production of lactic acid. In the absence of oxygen, pyruvate undergoes a process known as fermentation, where it is converted into lactic acid, keeping glycolysis ongoing by recycling NADH back into NAD+. This is a temporary solution for ATP production when oxygen is scarce, commonly occurring in muscle cells during intense exercise or in red blood cells, which lack mitochondria.
In contrast, if oxygen is present, pyruvate enters the mitochondria and undergoes a series of reactions in which it is transformed into acetyl CoA, signaling the start of aerobic respiration. Acetyl CoA then enters the citric acid cycle where complete oxidation occurs, eventually producing carbon dioxide and water.