LONG essays - 25 points each 1. Explain how the interaction of parathyroid hormone and calcitonin maintain homeostasis of the blood level of the calcium ion. Be sure to include their activity at the kidneys, digestive tract, and bone cells! Don't forget calcitriol's roll as well! . 2. Contrast, with 6 distinctive differences, intramembranous bone formation with endochondrial bone formation. 3. List, define, and give an example of the 4 organic molecules of life. INCLUDE ALL PRIMARY SUBDIVISIONS. Short essays - 15 points each.