JBL EMT Practice Exam 2025 – Comprehensive All-in-One Resource for Exam Success!

Breathing occurs as a result of a decrease in carbon dioxide, which increases the pH of the cerebrospinal fluid. This process is known as the negative feedback loop of the respiratory system. When carbon dioxide levels increase in the blood, it combines with water to form carbonic acid, leading to a decrease in pH. This decrease in pH is detected by chemoreceptors in the brain, which then signal the respiratory muscles to increase breathing rate in order to rid the body of excess carbon dioxide and restore pH balance. Therefore, choice A is the correct answer.

Among the other choices, a decrease in oxygen would not lead to an increase in pH, as oxygen levels primarily affect the respiratory rate to ensure proper oxygenation of tissues. An increase in carbon dioxide leads to a decrease in pH, not an increase. Additionally, an increase in oxygen would not lead to a decrease in pH; in fact, adequate oxygen levels help maintain physiological pH in the body.