Organisms which excrete ammonia

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. Animals that live in aquatic environments tend to release ammonia into the water. Animals that excrete ammonia are said to be ammonotelic.

Terrestrial organisms have evolved other mechanisms to excrete nitrogenous wastes. The animals must detoxify ammonia by converting it into a relatively nontoxic form such as urea or uric acid. Mammals, including humans, produce urea, whereas reptiles and many terrestrial invertebrates produce uric acid.

Animals that secrete urea as the primary nitrogenous waste material are called ureotelic animals. The urea cycle is the primary mechanism by which mammals convert ammonia to urea. Urea is made in the liver and excreted in urine. The urea cycle utilizes five intermediate steps, catalyzed by five different enzymes, to convert ammonia to urea, as shown in [link].

The amino acid L-ornithine gets converted into different intermediates before being regenerated at the end of the urea cycle. Hence, the urea cycle is also referred to as the ornithine cycle. The enzyme ornithine transcarbamylase catalyzes a key step in the urea cycle and its deficiency can lead to accumulation of toxic levels of ammonia in the body.

The first two reactions occur in the mitochondria and the last three reactions occur in the cytosol. Urea concentration in the blood, called blood urea nitrogen or BUN, is used as an indicator of kidney function. Evolution Connection Excretion of Nitrogenous Waste The theory of evolution proposes that life started in an aquatic environment. The first two reactions occur in the mitochondria, while the last three reactions occur in the cytosol. 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. Producing uric acid instead of urea is advantageous because it is less toxic and reduces water loss and the subsequent need for water. Key Terms urea : a water-soluble organic compound, CO NH2 2, formed by the metabolism of proteins and excreted in the urine guano : the excrement of seabirds, cave-dwelling bats, pinnipeds, or birds more generally purine : any of a class of organic heterocyclic base containing fused pyrimidine and imidazole rings; they are components of nucleic acids xanthine : a precursor of uric acid found in many organs of the body hypoxanthine : an intermediate in the biosynthesis of uric acid uric acid : a bicyclic heterocyclic phenolic compound, formed in the body by the metabolism of protein and excreted in the urine.

Nitrogenous Waste in Birds and Reptiles: Uric Acid Of the four major macromolecules in biological systems, both proteins and nucleic acids contain nitrogen. These include a ammonia, b urea, and c uric acid. Provided by : Boundless. October 17, Provided by : Wikipedia. Located at : en. December 2, Provided by : Boundless Learning.

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