[单选题]
The graph shows the changes in blood pH levels o
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b +hqbhj-3nra6t6r7nuring exercise and after exercise.
Which statement may explain the changes in blood pH shown in the graph?
A. The blood pH decreases due to the build-up of lactate.
B. The blood pH decreases due to muscle cells undergoing anaerobic respiration in the presence of oxygen.
C. The blood pH decreases due to the continued anaerobic respiration caused by oxygen debt.
D. The blood pH decreases due to the large yield of ATP produced during strenuous exercise.
参考答案:
A
本题详细解析:
Before exercise, the blood pH is higher than during and after exercise as the muscle cells are still undergoing aerobic cell respiration in the presence of oxygen. During exercise, oxygen levels start to decrease due to the muscle cells using more oxygen than normal to break down glucose. When oxygen levels decrease, muscle cells begin performing anaerobic respiration in the absence of oxygen (Choice B) and start producing lactate. Lactate (also known as lactic acid) decreases blood pH (Choice A).
During anaerobic respiration, a small yield of ATP is produced (Choice D) per molecule of glucose in the absence of oxygen. When available oxygen is used up quickly and oxygen debt occurs (Choice C) resulting in an increased demand for oxygen.
