Explain the factors that influence the type of nitrogenous waste excreted by animals

• Availability of water; animals in fresh water bodies have enough water available for dissolving any water products. They are able to dilute and excrete ammonia. For animals in terrestrial habitats, where acquisition of water is a problem, the nitrogen nous waters produced are less soluble. Animals excrete urea while insects which take in less water excrete uric acid.
• Solubility of nitrogen wastes; aquatic animals excrete more water-soluble ammonia while those in terrestrial habitat excrete less soluble urea or uric acid depending on the amount of water available to them. Terrestrial animals that are able to drink water excrete urea while those that depend on metabolic water such as insects excrete the insoluble uric acid
• Toxicity of the waste products; animals excrete nitrogenous waste with toxicity that either can be withstood by their tissues or that can easily be detoxified in the body. In most terrestrial animals, ammonia is very toxic. It is first converted to urea in the body by combining it with carbon dioxide. Urea is less toxic and can safely be excreted from the body without harming the body tissues. Freshwater animals however, excrete the toxic ammonia because they have enough water available for its dilution before excretion. Insect excrete uric acid which is least toxic.
• Animal body size; all organisms with big surface area to volume ratio excrete nitrogenous wastes that are more soluble in water and therefore can easily diffuse out through the body surface. For example, amoeba and other unicellular animals excrete ammonia. For large organisms, with small surface area to volume ratio, the other factors determine the nature of nitrogenous wastes excreted
• Production of enzymes necessary to convert ammonia to either uric acid and/or urea

Higher animals such as birds and mammals possess these enzymes and can excrete uric acid in birds and mainly urea in mammals