This leads to important questions as to whether such values should be more accurately determined, and could this be done by simply multiplying the LC 50 values by a lower number?
And if so, how low should it be? This is a difficult question to answer considering the potential implications of physiological disruptions on population dynamics are largely unknown and likely highly species specific. For example, does nitrogenous waste accumulation in certain water bodies lead to migrations or alterations in dominant populations?
And do they interact with other pollutants that are more persistent in nature? The importance of understanding these are particularly relevant considering nitrogenous wastes often reach high levels in estuaries and near shore coasts, where serve as important breeding grounds for various aquatic animals.
Indeed, our knowledge on potential effects of nitrogenous waste exposure on the reproductive capacity and population recruitment of aquatic animals is largely void.
Clearly, nitrogenous wastes are often overlooked as potential causes for affecting the distribution and abundance of natural populations in the past. With increasing anthropogenic discharge elevating nitrogen levels in various aquatic ecosystems worldwide, in our view, it is time research should be performed to examine the potential effects of elevated nitrogenous wasteson population dynamics of various aquatic animals. Such research, complemented by laboratory studies, should provide a more accurate and full picture on effects of nitrogenous wastes on aquatic animals and is likely to become increasingly important.
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Subscriber sign in You could not be signed in, please check and try again. Username Please enter your Username. Password Please enter your Password. Forgot password? Don't have an account? Sign in via your Institution. Urea Cycle : The urea cycle converts ammonia to urea in five steps that include the catalyzation of five different enzymes. Birds and reptiles have evolved the ability to convert toxic ammonia into uric acid or guanine rather than urea.
Of the four major macromolecules in biological systems, both proteins and nucleic acids contain nitrogen. During the catabolism, or breakdown, of nitrogen-containing macromolecules, carbon, hydrogen, and oxygen are extracted and stored in the form of carbohydrates and fats. Excess nitrogen is excreted from the body. Nitrogenous wastes tend to form toxic ammonia, which raises the pH of body fluids.
The formation of ammonia itself requires energy in the form of ATP and large quantities of water to dilute it out of a biological system. While aquatic animals can easily excrete ammonia into their watery surroundings, terrestrial animals have evolved special mechanisms to eliminate the toxic ammonia from their systems.
The animals must detoxify ammonia by converting it into a relatively-nontoxic form such as urea or uric acid. Nitrogen excretion : Nitrogenous waste is excreted in different forms by different species. These include a ammonia, b urea, and c uric acid. Birds, reptiles, and most terrestrial arthropods, such as insects, are called uricothelic organisms because they convert toxic ammonia to uric acid or the closely-related compound guanine guano , rather than urea.
In contrast, mammals including humans produce urea from ammonia; however, they also form some uric acid during the breakdown of nucleic acids. In this case, uric acid is excreted in urine instead of in feces, as is done in birds and reptiles. Uric acid is a compound similar to purines found in nucleic acids. It is water insoluble and tends to form a white paste or powder.
The production of uric acid involves a complex metabolic pathway that is energetically costly in comparison to processing of other nitrogenous wastes such as urea from the urea cycle or ammonia; however, it has the advantages of reducing water loss and, hence, reducing the need for water. Uric acid is also less toxic than ammonia or urea. It contains four nitrogen atoms; only a small amount of water is needed for its excretion.
Out of solute, it precipitates and forms crystals. The enzyme xanthine oxidase makes uric acid from xanthine and hypoxanthine, which in turn are produced from other purines.
Xanthine oxidase is a large enzyme whose active site consists of the metal, molybdenum, bound to sulfur and oxygen.
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