Excretion in Animals

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