NEET Biology Chapter 19

Excretory Products their Elimination

The process of excreting ammonia is Ammonotelism. Many bony fishes, aquatic amphibians and aquatic insects are ammonatelic in nature. Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions. Kidneys do not play any role in its removal. Terrestrial adaption necessitated the production of lesser toxic nitrogenous wastes like urea and ureic acid for conservation of water. Mammals many terrestrial amphibians and marine fishes mainly excrete urea and are called ureotelic animals. Ammonia produced by matabolism is converted into urea in the liver of these animals and released into the blood which is filtered and excreted out by the kidneys. Some amount of urea may be retained in the kidney matrix of some of these animals to maintain a desired osmolarity. Reptiles, birds, land snails, and insects excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water and are called uricotelic animals.

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