1. Cicadas living in the tropics have many more sweat pores than cicadas in cooler climates. Suggest how these differences might have arisen.

2. Imagine you are adrift at sea. Why would you dehydrate more quickly if you drank seawater to quench your thirst instead of fresh water?

3. Which of the substances listed on the left are excreted, and which are reabsorbed into the bloodstream?

4. Urinary tract infections frequently accompany sexually transmitted diseases, particularly in women. Why?

5. Would an excess or deficiency of renin be likely to cause hypertension (high blood pressure)? Cite a reason for your answer.

6. Why is protein in the urine a sign of kidney damage? What structures in the kidney are probably affected?

7. How could very low blood pressure impair kidney function?