Which animal body part is responsible for removing nitrogen?

• A. Liver
• B. Kidneys
• C. Spleen
• D. Lungs

Answer: (B)

Nitrogenous waste removal in animals hinges on how proteins are metabolized and how the body disposes of the resulting waste. When proteins are broken down, ammonia is produced, which is toxic if it stays in the bloodstream. The liver converts this ammonia into urea, a less toxic compound. The kidneys then filter the blood, remove urea and other nitrogenous wastes, and excrete them as urine. So the organ that actually disposes of nitrogenous waste from the body is the kidneys. The liver is essential for making urea, but the excretion happens through the kidneys; the lungs handle mostly carbon dioxide, and the spleen is involved in immune function and blood filtration rather than waste elimination.