Final answer:
Peripheral chemoreceptors respond directly to changes in arterial blood pH and CO2 concentration; thus, the correct answer is d) Answers a and b are correct. They sense significant decreases in dissolved oxygen levels as well, to ensure the body maintains respiratory homeostasis.
Step-by-step explanation:
Most peripheral chemoreceptors respond directly to changes in arterial blood pH levels, CO2 concentration, and O2 concentration. Specifically, peripheral chemoreceptors in the aortic arch and carotid arteries are sensitive to declines in pH, which is influenced by rising levels of carbon dioxide and hydrogen ions. Additionally, they respond to significant changes in the concentration of dissolved oxygen, not the oxygen bound to hemoglobin. When oxygen levels drop significantly, peripheral chemoreceptors stimulate increased respiratory activity to maintain homeostasis.
Hence, the correct answer to the question of what most peripheral chemoreceptors respond directly to changes in arterial blood is d) Answers a and b are correct. This is because the peripheral chemoreceptors primarily detect changes in pH levels and CO2 concentration; significant changes in O2 concentration also trigger a response, but only when there is a large decrease in dissolved oxygen.