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Zoology or Animal Biology

How do animals maintain water balance?


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September 12, 2011 9:12PM

Firstly, animals' cells need a small margine of 'salts' in their bodys to ensure enzymes and molecules can function efficiently, and to regulate pH of body fluids. Animals rely largely on their excretory organs (Liver & Kidneys) to remove waste and toxins, as well as control pH, ion concentrations and water balance.

Animals consume protein for energy and this contains nitrogen which is toxic to their systems. Nitrogenous waste first breaks down into ammonia, which is then converted to either urea or uric acid. Ammonia is toxic and it takes considerable energy to convert it into urea (which is less toxic) so usually, ammonia is only excreted by aquatic animals because it is diluted easily in their environment. Birds and reptiles excrete mostly uric acid, whereas mammals excrete their nitrogenous waste in the form of urea as their kidneys minimise water loss;an adaptation to living on land. The less water available, the more concentrated the waste.

Other adaptations to maintain water balance, although more 'behavioral', are seen in desert dwelling animals, e.g: Some have skin which absorbs rain and dew, some live under ground where the temperature is lower and has a higher water saturation content. Others do not drink, pant or sweat, and Kangaroo rats have learnt to collect dry grains at night, which absorb the water in the air in their burrows, thus enabling them to obtain this water when they eat.