Correct Option
The correct option is Mammals.
Explanation
Animals excrete nitrogenous wastes in different forms-ammonia, urea, or uric acid-depending on their habitat and water availability. Ureotelic animals are those that primarily excrete urea. Urea is less toxic than ammonia and requires a moderate amount of water for elimination, making it a suitable adaptation for terrestrial animals that have access to water but need to conserve it compared to aquatic environments.
Option Analysis
- Mammals Mammals: Correct. Mammals, including humans, are primarily ureotelic. Ammonia produced by metabolism is converted into urea in the liver (via the Ornithine cycle) and released into the blood, which is then filtered and excreted by the kidneys. This allows for significant water conservation compared to ammonia excretion.
- Birds Birds: Incorrect. Birds are uricotelic. They excrete uric acid, which is the least toxic nitrogenous waste and requires the least amount of water to be eliminated. It is excreted as a semi-solid paste or pellet to minimize water loss during flight and in arid conditions.
- Reptiles Reptiles: Incorrect. Most terrestrial reptiles (lizards, snakes) are uricotelic for the same reasons as birds-maximum water conservation.
- Insects Insects: Incorrect. Most insects are uricotelic. They excrete uric acid through Malpighian tubules to conserve water in their small bodies.
Key Takeaway
Nitrogenous Waste Classification:
- Ammonotelic: Excrete ammonia (highly toxic, requires large water volume). Example: Bony fishes, aquatic amphibians.
- Ureotelic: Excrete urea (moderate toxicity, moderate water loss). Example: Mammals, marine fishes, adult amphibians (frogs).
- Uricotelic: Excrete uric acid (least toxic, minimal water loss). Example: Birds, reptiles, insects.