Chemoreceptors are sensory cells responsive to chemical stimuli and detect changes in levels of which of the following?

• A. Temperature
• B. Light
• C. pH, O2, CO2
• D. Sound

Answer: (C)

Chemoreceptors sense chemical changes in the body's fluids, especially the composition of arterial blood and cerebrospinal fluid. They respond to shifts in pH and in the levels of gases such as oxygen and carbon dioxide. When CO2 rises or pH falls, central chemoreceptors (and peripheral ones to a extent) signal the respiratory centers to increase ventilation, helping to restore normal gas levels and acid-base balance. Low oxygen levels also stimulate these receptors to drive breathing. Temperature, light, and sound are detected by other types of receptors, not chemoreceptors, so they don’t fit this question.