Emergency Medical Technician (EMT) Intermediate Practice Exam

What type of metabolism occurs in body cells during intense exercise when oxygen is not available?

1. Aerobic metabolism

2. Utilization of carbohydrates

3. Anaerobic metabolism

4. Protein catabolism

The correct answer is: Anaerobic metabolism

During intense exercise, when oxygen is not available, the body relies on anaerobic metabolism to produce energy. Anaerobic metabolism occurs in the cytoplasm of cells and does not require oxygen to generate ATP (adenosine triphosphate), which is the primary energy currency of the cell. This process primarily breaks down glucose (carbohydrates), resulting in the production of lactic acid as a byproduct. At times of high demand for energy, such as during vigorous physical activity, the body can exceed its ability to supply sufficient oxygen for aerobic metabolism. As a result, it switches to anaerobic pathways to rapidly supply energy, although this method is less efficient in terms of ATP yield per glucose molecule compared to aerobic metabolism. In contrast, aerobic metabolism would not occur effectively in the absence of oxygen since it relies on oxygen to strengthen the oxidative phosphorylation pathway within the mitochondria. The utilization of carbohydrates refers to the broader concept of breaking down carbohydrates for energy, but does not specifically address the lack of oxygen during intense exercise. Protein catabolism involves the breakdown of proteins for energy, which is generally a secondary source and not a primary pathway during high-intensity exercise when carbohydrates are more readily available.