Excretory Products and Their Elimination - Notes | Class 11 | Part 1: Types of Excretion, Excretory Organs

Excretion is the elimination of metabolic wastes like ammonia, urea, uric acid etc. from the tissues.

Types of Excretion

1. Ammonotelism

  • Process of excretion of Ammonia (NH3).
  • Ammonotelic animals: Aquatic invertebrates, aquatic insects, bony fishes, aquatic amphibians etc.
  • NH3 is highly toxic. So, excretion needs excess of water.
  • NH3 is readily soluble in water and is excreted by diffusion through body surface or gill surfaces (in fishes) as ammonium ions.
  • Kidneys do not play any significant role in its removal.

2. Ureotelism

  • Process of excretion of urea.
  • Ureotelic animals: Cartilaginous fishes, terrestrial & semi-aquatic amphibians (frogs, toads etc.), aquatic & semi-aquatic reptiles (alligators, turtles), mammals etc.
  • In liver, NH3 is converted into less toxic urea. So, it needs only moderate quantity of water for excretion.
  • Some amount of urea may be retained in the kidney matrix of some animals to maintain a desired osmolarity.

3. Uricotelism

  • Process of excretion of uric acid.
  • It is water insoluble & less toxic. So, water is not needed for excretion.
  • Uricotelic animals: Insects, some land crustaceans, land snails, terrestrial reptiles & birds.
  • Ureotelism & uricotelism are needed for water conservation.

Some Excretory Organs in Animals

  • Protonephridia (flame cells): In Flatworms, rotifers, some annelids & cephalochordate (Amphioxus). Protonephridia are primarily for osmoregulation.
  • Nephridia: In Annelids. Help in the removal of nitrogenous wastes and osmoregulation.
  • Malpighian tubules: In Insects. Help in the removal of nitrogenous wastes and osmoregulation.
  • Antennal or green glands: In Crustaceans (prawn etc.)
  • Kidneys: In higher animals.

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