Page 1 - 5. Excretion in animals
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SAI International School

                                               Subject- Biology, Class-VII
                                          Topic-Transportation and Excretion
                                             Subtopic- Excretion in Animals
                                                       Lesson notes

               EXCRETION: The process of removal of metabolic wastes from the body is called excretion.

               EXCRETION IN ANIMALS

                   •  Unicellular organisms like Amoeba release waste by the process of diffusion.
                   •  Multicellular organisms like humans, fish, lion etc. use different mechanisms of
                       excretion.

               Based on the type of waste they excrete, different animals are categorized accordingly

                   •  AMMONOTELIC:  Organisms which release the nitrogenous waste in the form of
                       ammonia are called ammonotelic organisms. Ex. fish, frogs, etc.
                   •  UREOTELIC: Organisms which release the nitrogenous waste in the form of urea are
                       called ureotelic organisms. Ex. Human beings, other mammals.
                   •  URICOTELIC: Organisms which release the nitrogenous waste in the form of uric acid are
                       termed uricotelic organisms. Ex. Insects, reptiles, birds

               EXCRETION IN HUMANS
               In humans, different forms of waste products are eliminated from the body by different
               mechanisms.



                   •  Egestion – It is process by which solid indigested food products are removed along with
                       some other waste products formed in the digestion process.

                   •  Exhalation –It is a process in which gaseous waste such as carbon dioxide and excess
                       water vapour is expelled through the lungs.

                   •  Sweating – It helps to expel water, small amount of urea and salts through the sweat
                       gland present in the skin. Sweating also helps in cooling our body when the temperature
                       is high.

                   •  Excretion – It is the process of eliminating toxic nitrogenous wastes from the body. In
                       human beings, it is carried out mainly by the urinary system
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