[Campbell Biology P.1026] Based on the "Study Tip" that suggests categorizing nitrogenous was... | Practice Question

Based on the "Study Tip" that suggests categorizing nitrogenous wastes by "high," "medium," or "low" for Toxicity, Energy cost to produce, and Water loss during excretion, which statement accurately compares these properties?

  • A: Ammonia typically requires the lowest energy cost to produce, but results in the highest water loss during excretion.
  • B: Uric acid is generally the most toxic, requiring significant dilution and thus high water loss.
  • C: Urea represents a compromise, being less toxic than ammonia but more costly to produce than uric acid.
  • D: Organisms excreting uric acid are typically aquatic, due to the high solubility of this compound.

Explanation

Ammonia is the most toxic nitrogenous waste and thus requires a large amount of water for dilution and excretion, making it common in aquatic animals. However, its synthesis requires very little energy. Urea is less toxic than ammonia and requires moderate water for excretion, serving as a compromise for many terrestrial vertebrates. Its production is more energy-intensive than ammonia but less than uric acid. Uric acid is the least toxic and requires the least water for excretion due to its low solubility, making it suitable for animals in arid environments e.g., birds, reptiles, insects . Its synthesis is the most energetically costly.