Final answer:
Ammonia is converted to urea in mammals through the urea cycle, which requires less energy than converting ammonia to uric acid in other animals, making the statement in question false.
Step-by-step explanation:
Ammonia (NH3) is a byproduct of protein metabolism, highly toxic, and needs to be detoxified by conversion into other compounds. In mammals, the urea cycle is responsible for converting ammonia into urea. This process requires less energy than the conversion of ammonia to uric acid in birds, reptiles, and insects. Therefore, the statement that ammonia has a relatively high energy conversion cost compared to urea is false.