Answer to Question 1
ANS: D
The descending segment of the loop of Henle is highly permeable to water and so is involved in the reabsorption of water. The descending segment of the loop of Henle is not associated with the reabsorption of hydrogen ions or the secretion of either sodium or potassium.
Answer to Question 2
ANS: C
Principal cells reabsorb sodium and secrete potassium, and intercalated cells reabsorb potassium and bicarbonate and secrete hydrogen. This process is not associated with the secretion of sodi-um and chlorine, phosphate and calcium, or bicarbonate and carbonic acid.