Which of the following substances exhibits the highest toxicity?
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Answer: A. Ammonia
Explanation
Ammonia is a highly basic chemical compound that is extremely toxic to living biological tissues and cells. Excreting ammonia safely requires large volumes of water to dilute its high toxicity before elimination from the body. Because of this intense toxicity, aquatic animals excrete it directly, while terrestrial animals convert it into safer compounds. Nitrogenous waste products are generated during the metabolic breakdown of amino acids and nucleic acids in animals. Toxicity levels among nitrogenous wastes vary widely, dictating the evolutionary osmoregulatory strategies adopted by different species. Aquatic environments provide abundant water dilution, allowing fish to excrete toxic ammonia directly across their gill membranes.
Urea is significantly less toxic than ammonia and can be concentrated safely in mammalian urine before excretion. Uric acid exhibits very low toxicity and is excreted as a semi-solid paste by birds and reptiles to conserve water. Trimethylamine oxide is an organic osmolyte found in marine animals with low toxicity compared to raw ammonia.
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