Final answer:
A decrease in PCO2 will cause an increase in blood pH, making it more alkaline. This decrease in PCO2 can signal the respiratory system to decrease the rate of respiration.
Step-by-step explanation:
The level of carbon dioxide (PCO2) in the blood influences blood pH. An increase in PCO2 leads to a decrease in blood pH, making it more acidic.
Conversely, a decrease in PCO2 results in an increase in blood pH, making it more alkaline. The rate of respiration is influenced by changes in blood pH.
A decrease in PCO2 (resulting in a more alkaline blood pH) can signal the respiratory system to decrease the rate of respiration.