Xavier and Jill are practicing the 100-meter sprint. Which statement BEST describes the metabolic pathways their muscles will utilize to produce the quick energy needed for this intense anaerobic exercise? A. The pyruvic acid from glycolysis enters the mitochondria and is broken down in the Krebs cycle B. Glycolysis begins glucose metabolism, and in the absence of oxygen, lactic acid fermentation takes over. C. Glucose is converted to pyruvic acid, followed by the aerobic pathways of the Krebs cycle and the electron transport chain
The correct answer and explanation is :
The correct answer is B. Glycolysis begins glucose metabolism, and in the absence of oxygen, lactic acid fermentation takes over.
Explanation:
In a 100-meter sprint, the activity is very high-intensity, requiring rapid energy production. This type of exercise primarily relies on anaerobic metabolism due to the short duration and the muscles’ inability to get enough oxygen to meet the demand for energy. Here’s a breakdown of the metabolic pathways involved:
- Glycolysis: This is the initial metabolic pathway used during sprinting. Glycolysis is the breakdown of glucose (or glycogen stored in muscles) into pyruvic acid. This process occurs in the cytoplasm and does not require oxygen, making it anaerobic. Glycolysis produces a small amount of ATP (energy), which is used to fuel muscle contraction during the sprint.
- Lactic Acid Fermentation: In the absence of sufficient oxygen—since the muscles are working too quickly to receive oxygen in time—pyruvic acid produced in glycolysis cannot enter the mitochondria for the Krebs cycle. Instead, it is converted into lactic acid (lactate). This conversion regenerates NAD+, which is necessary for glycolysis to continue producing ATP. This process is called lactic acid fermentation.
- Energy Production: While the lactic acid fermentation pathway does not produce as much ATP as aerobic pathways (like the Krebs cycle and the electron transport chain), it is efficient for short bursts of intense activity, like sprinting. The lactic acid that accumulates in muscles contributes to muscle fatigue, but it allows for continued energy production during the anaerobic phase of the exercise.
Why the other options are incorrect:
- A. The pyruvic acid from glycolysis enters the mitochondria and is broken down in the Krebs cycle: This statement is true for aerobic exercise, but sprinting is anaerobic. The rapid pace does not allow sufficient oxygen delivery to muscle cells for aerobic metabolism to occur.
- C. Glucose is converted to pyruvic acid, followed by the aerobic pathways of the Krebs cycle and the electron transport chain: This option describes the process for activities like long-distance running, where oxygen supply can meet the muscle demand. However, during a 100-meter sprint, the body predominantly relies on anaerobic processes, not aerobic ones.