Different modes of excretion in animals: In our body cells numerous biochemical reactions take place from birth to death. During these biochemical reactions some byproducts are produced which can be used again in different purposes in our body. But some byproducts produced during these biochemical reactions are harmful for our body cells.
So they need to be removed as soon as possible and these harmful substances are excretory material. Now the harmful byproduct of cellular activity is not the same in all animals. These chemicals differ from animals to animals and the removal process of these chemicals are also different in different animals.
The removal process depends upon the chemical nature of the excretory material for a particular animal. Though there is variation in excretory material in different animals yet we can classify these chemicals to some major groups. Uric acid, ammonia, creatine, carbon dioxide, guanine, and urea are the major excretory products in different animals.
Modes of excretion:
As excretory products in different animals are different in chemical nature, we can categorise all animals in five group on the basis of different modes of excretion.
Uricotelic Animals: In this group main excretory product is uric acid. This mode of excretion is common in those animals who have to prevent more water loss. For example the animals who live in arid conditions like desert animals, birds, reptiles come in this category. In this case uric acid excretion occurs in solid or semi-solid pellets form which prevents a lot of water loss in excretion.
No doubt that it is an energy consuming process but water conservation is more important than energy in such conditions where water availability is very poor. This mode of excretion where uric acid is the main excretory product and mostly observed in arid condition is known as uricotelism.
Guanotelic Animal: Guanotelic term related to the major excretory product in this category, guanine. Most prominent example of this category is spiders. But some reptiles, birds and earthworms also come to this category as they excrete their excretory material in the form of guanine. Like uric acid, guanine also not easily dissolved in water and it goes outside from the body in semi-solid form and prevents water loss. This mode of excretion where the main excretory product is guanine is termed as guanotelism.
Ammonotelic Animal: Aquatic animals, like fish, crustaceans, porifera, protozoa, echinodermata can release their excretory material directly into water. For this their excretory material should be highly soluble in water.
These aquatic animals secret ammonia as their major excretory product which is highly soluble in water and mix with water easily are known as ammonotelic organisms and the process is known as ammonotelism. Ammonia is very toxic for the tissue and if it accumulates in tissues it can give very harmful effects. But it is highly soluble in water so it is easily removed from tissue after its secretion and does not consume very much energy in excretion.
Ureotelic Animal: Ureotelic term related to urea and in this category the main excretory product is urea. This process of excretion where uric acid is the main excretory product is known as ureotelism. In most of the mammals and amphibians ammonia is converted into urea in the liver and the urea mix with blood stream.
The urea then filtered from the bloodstream with the help of the kidney and the urea passed out from the body. Not all urea produced in the liver goes outside of the body some amount of urea remains in the kidney which plays a great role in maintaining osmolarity of the kidney. This osmolarity maintained by the kidney is very useful to impose counter current effects in nephrons.
Aminotelic Animal: In this category the main excretory product is excess amino acids and this process of excretion is termed as aminotelism. Some echinodermata and mollusca excrete excess amino acids as their excretory material because excess amino acids sometimes give harmful effects.
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Reference: Different modes of excretion in animals
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