Advanced Placement (AP) Biology Practice Exam

Which term describes the breakdown of carbohydrates resulting in lactic acid?

1. Glycolysis

2. Alcohol fermentation

3. Lactic acid fermentation

4. Cellular respiration

The correct answer is: Lactic acid fermentation

The correct answer is lactic acid fermentation, which specifically refers to the anaerobic process in which glucose is broken down into lactic acid and energy in the form of ATP. This occurs when oxygen is scarce or unavailable, such as during intense exercise in muscle cells. During lactic acid fermentation, glucose undergoes glycolysis, resulting in the production of pyruvate. In the absence of oxygen, pyruvate is then converted into lactic acid instead of being further processed through aerobic pathways. This process allows for the continued production of ATP, albeit less efficiently than aerobic respiration. In contrast, glycolysis refers to the initial metabolic pathway that breaks down glucose into pyruvate, and it occurs in both aerobic and anaerobic conditions, making it a broader term. Alcohol fermentation, on the other hand, results in ethanol and carbon dioxide as byproducts rather than lactic acid, and it involves different organisms like yeast. Cellular respiration encompasses all methods of ATP production, including both aerobic and anaerobic processes, but does not specifically describe the anaerobic pathway that leads to lactic acid production.