Excretory Products and their Elimination

Modes of excretion - ammonotelism, ureotelism, uricotelism

  • Metabolism of carbohydrates, Fats, amino acids and nucleic acids produces Excretory products.
  • CO2 and H2O, that are produced through the metabolism of CHO and fats are easy to remove through lungs (air), skin (sweat) or kidneys (urine).
  • But metabolism of proteins and nucleic acids produce nitrogenous waste materials such as ammonia, urea and uric acid, which are toxic and cannot be stored in the body for longer time.
  • The process of excreting ammonia (readily soluble) is ammonotelism.
    Eg: bony fishes, aquatic amphibians, aquatic insects.
  • Ammonia diffuses through gills (or) body membranes as ammonium ions, where kidneys do not play a major role in the removal.
  • Excretion of (water insoluble) urea is called as ureotilsm, where urea is less toxic.
    Eg: Mammals, Terrestrial amphibians, marine fishes.
  • Animals, that live in dry conditions excrete out uric acid are called uricotelic organisms in order to conserve water in their bodies. Uric acid is non toxic and completely insoluble in water.
    Eg: Reptiles, birds, insects and land snails.
  • Earthworms excrete out ammonia when sufficient water is available, whereas they excrete urea in dry environment. This mode of switching their excretory product based on the surroundings is called dual excretion.

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