What element is removed from the body by the respiratory system?

The respiratory system plays a crucial role in regulating the levels of gases in the body, primarily through the exchange of oxygen and carbon dioxide. When we inhale, oxygen from the air enters the lungs and is transported to the bloodstream, where it is used by the body's cells for energy production. Conversely, carbon dioxide, which is a byproduct of cellular metabolism, is transported from the cells back to the lungs, where it is expelled from the body during exhalation.

Carbon dioxide removal is essential for maintaining the body's acid-base balance and preventing respiratory acidosis, a condition that can occur when carbon dioxide levels rise in the bloodstream. As such, the primary function of the respiratory system in this context is the elimination of carbon dioxide, making it the correct answer to the question.

The other choices—nitrogen, helium, and carbon monoxide—either do not play a significant role in the respiratory exchange process or are handled differently by the body. Nitrogen makes up a large percentage of the atmosphere but is inert and not actively used or removed by the respiratory system. Helium, while it can be inhaled and exhaled, is not a normal component of respiration. Carbon monoxide, though it can be harmful when inhaled, does not get expelled