In smaller organisms there are different ways of excretion of waste materials. 

This depends on the arrangement of the body of the organism.


  • In unicellular organisms like amoeba, wastes (like CO 2 ) are let out directly by diffusion from the body. Nitrogenous wastes like ammonia and water are removed by the contractile vacuole .

In multicellular organism like fishes or birds, nitrogenous wastes are of different types : 

  • In Earthworms , tubular structures called nephridia are the excretory organs. It’s moist skin also expels CO 2
  • Fishes have ammonia as their waste product
  • Birds excrete waste in the form of uric acid
  • Human beings have urea as their nitrogenous waste 


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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo