Question

explain why mammals excrete urea and not ammonia​

Answer 1

Explanation:

Urea is less toxic and requires less water to remove from organism (so it's better in terrestrial environment) but it requires more energy to produce. And uric acid is most costly in terms of energy but requires the least amount of water to remove.

Answer 2

Answer:

This mechanism is important to prevent the loss of water, to maintain blood pressure, and to maintain a suitable concentration of sodium ions in the blood plasmas. The urea cycle is the primary mechanism by which mammals convert ammonia to urea. Urea is made in the liver and excreted in urine.