Question

On a backpacking trip, Kenny hikes all day at a steady pace, covering 30 kilometers and burning 4000 Calories. At the school track, Janelle runs the 100-meter sprint in 13.5 seconds, burning 10 Calories. Afterward, Janelle’s leg muscles are aching and she is breathing hard, while Kenny maintains normal breathing all day, even though he burns 400 times more calories than Janelle. Which two statements offer the BEST explanation for this phenomenon? A. If the aerobic pathway—cellular respiration—cannot meet the energy demand, then the anaerobic pathway—lactic acid fermentation—starts up, resulting in lactic acid buildup and "oxygen debt." B. Aerobic cellular respiration produces more energy, but its use is limited because of lactic acid buildup in the muscles and the resulting "oxygen debt." C. After about 90 seconds of intense exercise, the muscles become depleted of oxygen, and anaerobic respiration can no longer function to produce ATP, resulting in "oxygen debt." D. The rate of energy demand determines how the muscles will obtain energy, either from cellular respiration or from lactic acid fermentation if not enough oxygen is present.

Answer 1

A. If the aerobic pathway—cellular respiration—cannot meet the energy demand, then the anaerobic pathway—lactic acid fermentation—starts up, resulting in lactic acid buildup and "oxygen debt."

D. The rate of energy demand determines how the muscles will obtain energy, either from cellular respiration or from lactic acid fermentation if not enough oxygen is present.

Step-by-step explanation:

It is important to consider that Kenny hikes all day but at a steady pace, whereas Janelle runs very fast. So Kenny's case, the supply of oxygen is sufficient to maintain aerobic respiration within the muscle cells. During this process only CO2, Water, and ATP are produced; therefore, there is no oxygen debt. We should keep in mind that the body shifts to anaerobic metabolism only when the supply of oxygen is limited.

In Janelle's case, running fast would need energy at higher rates and the supply of oxygen would not be sufficient to generate a high amount of ATPs. Therefore, to compensate for this deficiency, cells will start fermenting glucose to lactic acid and produce ATP and maintain energy demands. This lactic acid causes fatigue and this is why Janelle has aching and breathing hard. Breathing hard is also automatic reflux to inhale more oxygen and meet oxygen demands but even breathing hard would not be able to make it and the body will shift to anaerobic respiration automatically.