Which group of animals is known to have concentrated urine that is almost solid and white?

Which group of animals is known to have concentrated urine that is almost solid and white?

• A. Gerbils and nonhuman primates
• B. Rabbits and gerbils
• C. Birds and mice
• D. Reptiles and birds

Answer: (D)

Birds and reptiles are uricotelic, meaning they excrete nitrogen mainly as uric acid. Uric acid is relatively insoluble, so their urine is highly concentrated and often looks like a white, chalky paste—almost solid. This adaptation helps conserve water, which is especially important for animals that may have limited access to liquids. In contrast, most mammals and rodents excrete nitrogen as urea in a liquid urine, which is typically clear to pale yellow rather than white and paste-like. So the white, almost solid urine is characteristic of birds and reptiles.

Birds and reptiles are uricotelic, meaning they excrete nitrogen mainly as uric acid. Uric acid is relatively insoluble, so their urine is highly concentrated and often looks like a white, chalky paste—almost solid. This adaptation helps conserve water, which is especially important for animals that may have limited access to liquids. In contrast, most mammals and rodents excrete nitrogen as urea in a liquid urine, which is typically clear to pale yellow rather than white and paste-like. So the white, almost solid urine is characteristic of birds and reptiles.