The most effective molecule for nitrogenous waste disposal in desert animals would be __________.

• A. ammonia because it uses less energy to make than uric acid or urea
• B. urea because it is less toxic than uric acid
• C. uric acid because it takes less energy to make than urea
• D. ammonia because it is the most soluble of all the nitrogen-containing metabolic waste products
• E. uric acid because it requires very little water for excretion

Answer: (E)

Verified step by step guidance

1. Understand the context: Desert animals need to conserve water due to their arid environment. Therefore, the form of nitrogenous waste they excrete should minimize water loss.
2. Review the properties of the nitrogenous waste products: Ammonia is highly toxic and requires a lot of water to be excreted, making it unsuitable for desert animals. Urea is less toxic and requires less water than ammonia but more than uric acid. Uric acid is the least toxic and requires the least amount of water for excretion.
3. Consider energy expenditure: While ammonia is the least energy-intensive to produce, its high water requirement makes it impractical for desert animals. Urea requires more energy to produce than ammonia but less than uric acid. Uric acid, although the most energy-intensive to produce, is advantageous in water conservation.
4. Evaluate the trade-offs: Desert animals prioritize water conservation over energy expenditure due to their environment. Therefore, the ability to excrete waste with minimal water loss is more critical than the energy cost of producing the waste.
5. Conclude with the best option: Given the need to conserve water, uric acid is the most effective molecule for nitrogenous waste disposal in desert animals because it requires very little water for excretion, despite its higher energy cost.