1. The receptors for thirst are located in a part of the brain called the hypothalamus. These receptors, called osmoreceptors, are stimulated by an increase in blood osmolality. Imagine a man who has just landed on a desert island. Trace the course of events leading to his sensation of thirst. Can he satisfy his thirst by drinking seawater? Explain

2. Explain the etiology of phenylketonuria (PKU).

3. Using letters A, B, C, D, and E for molecules, illustrate how these would interrelate in an unbranched metabolic pathway. Then, illustrate a metabolic pathway in which C branches to form D and E. Describe how your two pathways would be affected by an inborn error of metabolism between C and D.

4. If a man with sickle-cell disease marries a woman with sickle-cell trait, what is the probability that their children will have a (a) sickle-cell trait (b)sickle-cell disease