- Among the following which groups of organisms are not uricotelic?
(1) Mammals (2) Birds
(3) Reptiles (4) Insects
In the animal kingdom, the excretion of nitrogenous waste is a critical physiological process shaped by environment, water availability, and evolutionary lineage. Animals can be classified as ammonotelic, ureotelic, or uricotelic based on their major nitrogenous waste. Here, we focus on which of the groups listed is not uricotelic.
Nitrogenous Waste Types
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Ammonotelic: Excretion of ammonia; found mostly in aquatic animals due to need for ample water.
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Ureotelic: Excretion of urea; characteristic of mammals and adult amphibians.
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Uricotelic: Excretion of uric acid; seen in birds, reptiles, and insects—adapted for water conservation.
Primary Excretory Product in Mammals
Mammals are ureotelic. This means:
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They convert toxic ammonia to urea in the liver using the urea cycle, a less toxic and highly soluble compound.
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Urea is eliminated by kidneys as a major component of urine, requiring more water relative to uric acid elimination.bio.libretexts+2
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Uric acid is also produced as a byproduct of purine metabolism but only in very small quantities; it is not the primary excretory product.
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Mammals have adapted kidneys that can concentrate urine for moderate water conservation, but not as effectively as uricotelic animals.opentextbc+2
Comparison with Other Groups
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Birds: Uricotelic. Excrete uric acid as insoluble white paste, minimizing water usage—key for flying and dry habitats.bio.libretexts
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Reptiles: Uricotelic. Like birds, excrete uric acid as a water-saving strategy for survival in arid environments.bio.libretexts
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Insects: Mostly uricotelic, highly adapted for water conservation in terrestrial ecosystems.byjus+1
Summary Table: Nitrogenous Waste by Organism Group
Group Main Excretory Product Type Water Conservation Mammals Urea Ureotelic Moderate Birds Uric Acid Uricotelic High Reptiles Uric Acid Uricotelic High Insects Uric Acid Uricotelic High Ecological Significance
Water conservation through uricotelism is crucial for animals that live in arid regions or have water challenges (birds during flight, reptiles in deserts, terrestrial insects). Mammals, however, evolved in more water-abundant settings and so rely on urea excretion, which is less energy-expensive but requires more water.
Conclusion
Among the listed groups, mammals stand out as not uricotelic—they are ureotelic, excreting urea as their primary nitrogenous waste. This distinction is fundamental in physiology and underpins differing survival strategies across environments.
Correct Answer: (1) Mammals
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