I Excretory System A) Function - overcome problem of water balance and buildup of toxic wastes in the body 1) maintain stable levels of water and salts in the blood 2) Excrete nitrogenous wastes from the body B) Problems for different organisms 1) Freshwater fish - plenty of water, problems with diffusion, constantly urinating and not drinking 2) Marine fish - problems with diffusion (water loss), constantly drinking water 3) Terrestrial organsims - face water loss and dessication C) How does it accomplish this? 1) Excretes nitrogenous waste products in a water solution a) Ammonia in fish b) Uric acid in birds and insects c) dilute urea in mammals, amphibians, sharks 2) Physiological strategies a) freshwater fish b) saltwater fish c) flatworms - flame cells d) insects - Malphigian tubules e) Vertebrates - kidney basic unit of the human/vertebrate kidney - nephron
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