1. Which hormone primarily regulates the blood calcium levels? A. Insulin B. Thyroxine C. Parathyroid hormone D. Cortisol Answer: C. Parathyroid hormone Rationale: Parathyroid hormone is the main regulator of calcium levels in the blood, as it increases the concentration by promoting the release of calcium from bones, increasing absorption in the intestines, and conserving calcium in the kidneys. 2. What is the role of the alveoli in the respiratory system? A. To transport oxygen to the bloodstream B. To warm and humidify the air C. To facilitate the exchange of gases D. To produce respiratory mucus Answer: C. To facilitate the exchange of gases Rationale: The alveoli are tiny sacs within the lungs where the exchange of oxygen and carbon dioxide occurs, allowing for gas exchange with the bloodstream. 3. During the stress response, what immediate action does the sympathetic nervous system trigger? A. Decreased heart rate B. Increased digestive activity C. Release of glucose reserves D. Constriction of the pupils Answer: C. Release of glucose reserves Rationale: The sympathetic nervous system initiates the 'fight or flight' response, which includes the release of glucose reserves for immediate energy.