SAT Subject Biology Practice Question 212: Answer and Explanation
2. Mammals and sharks produce a compound called urea. What is the function of urea?
A. It raises the pH level of the blood.
B. It sends signals from cells that produce it to other organs.
C. It provides energy to some cells and tissues.
D. It prevents ammonia from building up in the body.
E. It eliminates water from the bloodstream.
Correct Answer: D
The production of urea serves to chemically join ammonia and carbon dioxide, thereby converting it to a relatively harmless compound. This prevents ammonia, which is toxic, from accumulating in the bloodstream and allows it to be eliminated without releasing large quantities of water.