In the lock-and-key model of enzyme action, the fits into the of the enzyme.

a.) product; substrate
b.) active site; product
c.) substrate; active site
d.) active site; substrate

Which of the following best describes the purpose of the parathyroid hormone? a. it decreases the blood calcium level and decreases blood phosphorus level. b. it decreases the blood calcium level and increases the blood phosphorus level. c. it increases the blood calcium level and increases blood phosphorus level. d. it increases the blood calcium level and decreases blood phosphorus level.