Which of the following is considered the most important chemical regulator of respiration in humans?

• A. Nitrogen (N_2)
• B. Hydrogen ions (H^+)
• C. Carbon dioxide (CO_2)
• D. Oxygen (O_2)

Answer: (C)

Verified step by step guidance

1. Understand that respiration in humans is primarily regulated by the body's need to maintain homeostasis, especially the balance of gases and pH in the blood.
2. Recognize that while oxygen (O_2) is essential for cellular respiration, the body’s respiratory control centers are more sensitive to changes in carbon dioxide (CO_2) levels rather than oxygen levels.
3. Know that carbon dioxide (CO_2) dissolves in blood to form carbonic acid, which dissociates into hydrogen ions (H^+) and bicarbonate ions, affecting blood pH.
4. Realize that the increase in hydrogen ion concentration (H^+) from CO_2 influences chemoreceptors in the brain, which then adjust the rate and depth of breathing to regulate CO_2 levels and maintain pH balance.
5. Conclude that carbon dioxide (CO_2) is considered the most important chemical regulator of respiration because it directly affects blood pH and stimulates respiratory control mechanisms.