Final answer:
An increase in PCO₂ causes bronchioles to dilate and systemic arterioles to constrict, optimizing airflow and blood flow for better gas exchange. The answer is option C.
Step-by-step explanation:
The local increase in partial pressure of carbon dioxide (PCO₂) will lead to physiological changes in the respiratory system. Specifically, an increase in PCO₂ will cause the bronchioles to dilate, which is a mechanism to increase airflow and exhalate carbon dioxide more effectively.
Conversely, the systemic arterioles will constrict in response to high levels of CO₂, which helps to redirect blood flow to areas of the lungs that are better ventilated, optimizing the gas exchange process. Therefore, the correct response to the student's question is C. dilate and systemic arterioles to constrict.