Excess amino acids are converted into urea by the

Step 1: Analyze the question The question asks which organ converts excess amino acids into urea. This is a process called deamination, followed by the urea cycle.

Step 2: Explain the concept The body cannot store excess amino acids, so it breaks them down:

1. Deamination: The amino group (-NH₂) is removed from the amino acid. This produces ammonia (toxic) and a keto acid, which can be used for energy or converted to carbohydrate or fat.
2. Urea formation (ornithine cycle): Ammonia is combined with carbon dioxide to form urea, which is much less toxic.
3. Excretion: Urea is carried in the blood to the kidneys, which filter it out and excrete it in urine.

Step 3: Evaluate the options

• A. Heart: It pumps blood and has no role in making urea.
• B. Kidney: It excretes urea but does not make it. This is a common trap.
• C. Liver: It carries out deamination and converts ammonia to urea. ✔
• D. Muscles: They produce movement. They do produce some waste (such as creatinine), but they do not make urea.
• E. Spleen: It destroys old red blood cells and stores blood, and it has no role in urea formation.

Step 4: Answer The liver is the organ that converts excess amino acids into urea.

💡 Exam tip: Remember "Liver makes, Kidney takes": the liver makes urea, and the kidney takes it out of the blood for excretion. WAEC, NECO, and JAMB often test this difference.