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| * Some organisms excrete nitrogen directly as ammonia | | * Some organisms excrete nitrogen directly as ammonia |
| + | * They are known as '''ammonotelic''' organisms |
| * This is how fish and aquatic amphibians excrete nitrogenous waste | | * This is how fish and aquatic amphibians excrete nitrogenous waste |
− | * Relatively toxic but it is better tolerated by aquatic animals | + | * Relatively toxic but it is better tolerated by aquatic animals due to dilution |
| * 400ml of water is also excreted per gram of ammonia making this an unrealistic option for terrestrial organisms | | * 400ml of water is also excreted per gram of ammonia making this an unrealistic option for terrestrial organisms |
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| ====Urea==== | | ====Urea==== |
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| * Some animals process ammonia into urea | | * Some animals process ammonia into urea |
| + | * They are known as '''ureotelic''' organisms |
| * Mammals and terrestrial amphibians | | * Mammals and terrestrial amphibians |
| * 40ml of water is excreted per gram of urea excreted | | * 40ml of water is excreted per gram of urea excreted |
| + | * Urea is very soluble and non-toxic |
| + | |
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| ====Uric Acid==== | | ====Uric Acid==== |
− | * Referred to as Uricotelism | + | * Referred to as '''Uricotelism''' |
| * Urea is further processed to uric acid | | * Urea is further processed to uric acid |
| * Carried out by birds and reptiles | | * Carried out by birds and reptiles |
| * Only 8ml of water is co-excreted per gram | | * Only 8ml of water is co-excreted per gram |
− | * Highly insoluble | + | * Highly insoluble and less toxic than ammonia, though it can precipitate into body cavities |
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| ==Fish== | | ==Fish== |