Final answer:
Calcium regulates cellular metabolism by influencing enzymes and hormonal responses. It acts as a second messenger in signaling pathways and plays a role in muscle contraction, nerve impulse transmission, and blood clotting. The parathyroid glands are involved in regulating blood calcium levels.
Step-by-step explanation:
Calcium helps regulate cellular metabolism by influencing the activities of various enzymes and hormonal responses. Calcium acts as a second messenger in signaling pathways, affecting the activity of enzymes and regulating processes such as muscle contraction, nerve impulse transmission, and blood clotting. It is also involved in the regulation of blood calcium levels by the endocrine system, specifically the parathyroid glands.