Which nitrogenous waste requires the least amount of water per gram of its excretion?
Correct answer: C. Uric acid
- A. Ammonia
- B. Urea
- C. Uric acid
- D. Creatinine
Explanation
Uric acid is almost insoluble and can be excreted as a paste, so it needs the least water per gram of nitrogen, which is why birds, reptiles and insects use it. Ammonia is the most toxic and must be diluted with a great deal of water, and urea lies between the two.
This question appeared on the UHS MDCAT 2026 paper, which you can sit online with every answer explained.
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About Excretion
Excretion removes metabolic wastes such as carbon dioxide, urea and excess salts, and differs from egestion, which removes undigested food. Questions cover kidney structure, nephron ultrafiltration, selective reabsorption and urine formation, along with the excretory roles of the lungs, skin and liver in maintaining homeostasis.
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