Which of the following is NOT a primary function of the respiratory system?

The primary functions of the respiratory system primarily revolve around gas exchange, temperature regulation, and sound production. The correct answer identifies that the formation of blood cells is not a function of the respiratory system. Instead, this process occurs in the bone marrow, where red and white blood cells are produced.

The respiratory system's main role is the exchange of oxygen and carbon dioxide, which is essential for cellular respiration and maintaining homeostasis. Additionally, regulating body temperature occurs through the moisture content of the air we breathe and the evaporation of water in the respiratory tract. Sound, or voice production, is facilitated by the larynx (voice box) as air passes through it, which is integral to vocalization. These functions underscore the complexity of the respiratory system, highlighting its essential role in the body, while the formation of blood cells distinctly falls outside its responsibilities.