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Excretion - Salt and Water Balance and Nitrogen Excretion...

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Salt and Water Balance and Nitrogen Excretion
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Tissue Fluid and Water Balance Excretory organs control osmolarity and volume of tissue fluid by excreting excess solutes and retaining others that are valuable or in short supply. Terrestrial organisms also use excretory organs to eliminate waste products of nitrogen metabolism. The output is called urine . Organisms have diverse excretory systems depending on the environments in which they live.
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Excreting Nitrogenous Wastes Fats and carbohydrates break down into water and CO 2 , which are easily eliminated. Proteins and nucleic acids contain nitrogen. Breakdown of these produces nitrogenous waste. Ammonia is the most common nitrogenous waste product and is highly toxic. It must be quickly eliminated or converted
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Figure 51.3 Waste Products of Metabolism
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Excreting Nitrogenous Wastes Aquatic animals continuously excrete ammonia. It is very soluble in water and diffuses rapidly across gill membranes. These animals are called ammonotelic .
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Vertebrate Excretory Systems The kidney is the major excretory organ of vertebrates. The functional unit of the vertebrate kidney is the nephron . Each human kidney has about a million nephrons. The nephron probably evolved to excrete excess water. But adaptations of different vertebrate groups have allowed them to exploit environments in which water must be conserved and salts excreted.
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Figure 51.10 Concentrating the Urine
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