Final answer:
The liver assists the kidneys in eliminating protein byproducts by converting ammonia to urea, which the kidneys then excrete.
Step-by-step explanation:
The organ that assists the kidneys in the process of eliminating protein byproducts that are broken down into ammonia is the liver. The liver plays a critical role in metabolism and detoxification. It converts ammonia into a less toxic substance called urea, which is then excreted by the kidneys as part of the urine. This collaboration between the kidneys and the liver is essential for the excretion of waste products produced by protein metabolism.