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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
