Question

In the ornithine cycle, which of the following wastes are removed from the blood?

• A. Ammonia and urea
• B. CO₂ and urea
• C. Urea and urine
• D. CO₂ and ammonia

Answer 1

The correct option is D

CO₂ and ammonia

Urea is formed in the liver by a cyclic process called the urea cycle. Three amino acids, ornithine, citrulline and arginine, participate in this process. Ornithine combines with ammonia and carbon dioxide to form citrulline and water. Citrulline combines with more ammonia to form arginine and water. Arginine is decomposed to form urea and ornithine in the presence of the enzyme arginase and water. Ornithine is set free for reuse in the urea cycle.