Final answer:
The primary drive to breathing during rest is the level of carbon dioxide in the blood acting through hydrogen ions at the central chemoreceptors, which signal the respiratory centers to adjust breathing rate and depth. The correct choice of option is 4) None of the above
Step-by-step explanation:
The primary drive to breathing under normal resting conditions is the concentration of carbon dioxide (CO₂) in the blood, which acts through hydrogen ions (H⁺) at the central chemoreceptors. These chemoreceptors, located in the brain and brainstem, sense changes in carbon dioxide and hydrogen ion concentrations, signaling the respiratory centers to modulate respiration.
In response to increased levels of carbon dioxide, the central chemoreceptors stimulate the respiratory centers, resulting in increased breathing rate and depth to expel more CO₂. Conversely, with low levels of carbon dioxide, respiration slows. On the other hand, the peripheral chemoreceptors, located in the carotid arteries and aortic arch, respond to large changes in blood oxygen levels. Though important, the drive from oxygen levels usually becomes significant only when there is a fairly large drop in the partial pressure of oxygen, which then prompts these chemoreceptors to increase respiratory activity.