AAMC FL Practice Exam

What is formed during anaerobic respiration in the cytoplasm?

1. Acetyl CoA

2. Lactic acid

3. Pyruvic acid

4. Glucose

The correct answer is: Lactic acid

During anaerobic respiration in the cytoplasm, lactic acid is formed primarily in muscle cells after intense exercise when oxygen levels are low. In this process, glucose undergoes glycolysis, which breaks it down into pyruvic acid. Under anaerobic conditions, pyruvic acid is then converted into lactic acid through the process of lactic acid fermentation. This conversion allows for the regeneration of NAD+, which is essential for the continuation of glycolysis and the production of ATP in the absence of oxygen. The presence of lactic acid as a byproduct also explains the muscle fatigue experienced during strenuous activity. The formation of lactic acid is particularly important in short bursts of activity where energy demand surpasses the supply of oxygen for aerobic respiration. Other options involve different metabolic pathways: Acetyl CoA is formed from pyruvic acid during aerobic respiration when oxygen is present, while glucose is the starting material for glycolysis. Pyruvic acid is an intermediate product of glycolysis, so although it is produced during the process, it does not directly represent the end product of anaerobic respiration in the cytoplasm.