Final answer:
Cells switch to anaerobic respiration or fermentation to generate ATP when oxygen is scarce. Red blood cells, which rely on glycolysis due to the lack of mitochondria, would be severely impacted if glycolysis were blocked as they cannot produce ATP otherwise.
Step-by-step explanation:
When an animal is running and does not have enough oxygen available for aerobic cellular respiration, the cells will shift to a process called anaerobic respiration or fermentation. This process allows cells to continue generating ATP through glycolysis by converting pyruvate into either lactic acid or ethanol, regenerating NAD* in the process. This is vital as NAD* is required for glycolysis to proceed, although it yields much less ATP compared to aerobic respiration.
Human red blood cells (erythrocytes) lack mitochondria and therefore rely solely on glycolysis to produce ATP. If glycolysis were blocked in these cells, red blood cells would not be able to produce the necessary ATP they need, as they cannot tap into other cellular respiration processes. They have no alternative sources of free energy and would become nonfunctional, leading to serious health consequences, considering their role in oxygen transport.