Which structure of the excretory system in humans is responsible for converting ammonia into urea?

A. Liver

B. Lungs

C. Skin

D. Kidneys

D. Kidneys

The two bean shaped structures or organs located in left and sides at the back of the abdominal cavity are said to be kidneys.

The main functions of the kidney are, filtration, reabsorption, secretion and excretion (production of urine).

The small structural and functional unit of the kidney is nephron.