Biology 2010 Student Edition

Published by Prentice Hall
ISBN 10: 9780133669510
ISBN 13: 978-0-13366-951-0

Chapter 27, Animal Systems I - Assessment - 27.4 Excretion - Understand Key Concepts - Page 803: 27


Animals convert ammonia into urea or uric acid because these two substances are less toxic to cells than ammonia.

Work Step by Step

Ammonia, uric acid, and urea are all nitrogenous compounds. Cells produce ammonia as a byproduct of breaking down proteins. Ammonia is extremely toxic to cells and can kill them; however, ammonia cannot be disposed of right away. Nitrogenous wastes cannot stay in this form in the bodies of animals; therefore, while nitrogenous wastes must stay in the body, they have to be changed into a form that the body can tolerate. These more tolerable, less toxic forms of nitrogen are uric acid (formed in insects, reptiles, and birds) and urea (formed in mammals and certain amphibians).
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