USA Biology Olympiad (USABO) Practice Exam

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If an animal experiences acidosis, how must the ventilation rate change to normalize pH?

  1. Ventilation rate decreases, arterial PCO2 decreases

  2. Ventilation rate increases, arterial PCO2 decreases

  3. Ventilation rate remains constant, arterial PCO2 increases

  4. Ventilation rate decreases, arterial PCO2 increases

The correct answer is: Ventilation rate increases, arterial PCO2 decreases

In a state of acidosis, the pH of the blood decreases, leading to an increase in hydrogen ion concentration. The body has mechanisms to restore normal pH, one of which involves adjusting ventilation rates to regulate carbon dioxide levels in the blood. During acidosis, there is often an accumulation of carbon dioxide (CO2) due to metabolic processes, which can further lower pH. To counteract this acidosis, the body increases the ventilation rate. This increase in ventilation is aimed at expelling more CO2 from the body, which helps to decrease the arterial PCO2 (partial pressure of carbon dioxide in arterial blood). Lowering the arterial PCO2 reduces the concentration of carbonic acid in the blood, thereby increasing pH back toward normal levels. Thus, the correct response indicates that during acidosis, an increase in the ventilation rate leads to a decrease in arterial PCO2, helping to restore acid-base balance.

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