Name: nitrogen waste in animal excretion
Uploaded: 2019-08-01T08:29:34.000Z
Duration: 2 min 24 s
Channel: JoVE

Biological macromolecules, carbohydrates, lipids, proteins, and nucleic acids, are the most important large molecules in the body.

Proteins and nucleic acids contain nitrogen that is often a byproduct when these molecules are broken down. Excess nitrogen in the body tends to form ammonia, which is highly toxic and must be removed either directly or after conversion to urea or uric acid.

Most aquatic animals directly release ammonia into their environment. Much of the ammonia is lost to diffusion, so this process is not energy-intensive. However, ammonia can only be tolerated at low concentrations, so these animals require lots of water to dilute it in.

For many organisms, this water cost is too hefty. Mammals, many adult amphibians, and some marine organisms convert ammonia into urea before expelling it from the body.

Urea is much less toxic than ammonia, so it requires less water for its removal. However, converting ammonia into urea requires energy.

Birds, reptiles, and insects convert ammonia primarily into uric acid. Uric acid can be excreted in a more solid form, requiring very little water. However, converting ammonia into uric acid is even more energy-intensive than conversi

comparative excretory systems

Comparative Excretory Systems

Animals have evolved different strategies for excretion, the removal of waste from the body. Most waste must be dissolved in water to be excreted, so an animal&rsquo;s excretory strategy directly affects its water balance.

Nitrogenous wastes are some of the most significant forms of animal waste. Nitrogen is released when proteins and nucleic acids are broken down for energy or conversion into carbohydrates and fats. Proteins are broken down into amino acids and nucleic acids into nitrogenous bases. The nitrogen-containing amino groups of amino acids and nitrogenous bases are then converted into nitrogenous wastes.

Typical nitrogenous wastes released by animals include ammonia, urea, and uric acid. These excretory strategies involve tradeoffs between conserving energy and water.

The various nitrogenous wastes reflect distinct habitats and evolutionary histories. For example, most aquatic animals are ammonotelic, meaning they directly excrete ammonia. This approach is less energy-intensive than converting ammonia into urea or uric acid before excretion, but also requires more water. For terrestrial organisms, which face perhaps no more significant regulatory threat than dehydration, water conservation is worth the extra energy cost.

Ureotelic animals, like mammals and sharks, convert ammonia into urea before excretion. Urea is less toxic than ammonia and requires less water for removal from the body. Many amphibians that move from aquatic to terrestrial habitats excrete ammonia primarily as tadpoles but excrete mostly urea as adults on land.

Uricotelic organisms, including reptiles, birds, and many insects, convert ammonia into uric acid before excretion. Uric acid is not water-soluble and is excreted as a paste or powder, using very little water. Uric acid is even less toxic than urea. However, converting ammonia into uric acid requires even more energy than conversion into urea.

These different excretory strategies allow animals to meet the unique water and energy demands of their environments.

Animals have evolved different strategies for excretion, the removal of waste from the body. Most waste must be dissolved in water to be excreted, so an ...

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Osmoregulation and Excretion

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nitrogen waste in animal excretion

Animals use different excretory strategies to remove waste from the body. These strategies matter because most waste must be dissolved in water before it can leave the body. That means excretion is closely tied to water balance.

Nitrogenous wastes are some of the most important animal wastes. Nitrogen is released when proteins and nucleic acids are broken down for energy or turned into carbohydrates and fats. Proteins become amino acids, and nucleic acids become nitrogenous bases. The nitrogen-containing amino groups from these molecules are then converted into wastes.

Animals commonly release ammonia, urea, or uric acid. Most aquatic animals are ammonotelic, which means they excrete ammonia directly. This uses less energy than changing ammonia into another compound, but it also needs more water. For aquatic species, that tradeoff often fits their environment.

Terrestrial animals face a different problem because they must limit dehydration. Ureotelic animals, including mammals and sharks, convert ammonia into urea before excretion. Urea is less toxic than ammonia and needs less water to remove. Many amphibians show this shift too, because tadpoles mainly excrete ammonia in water, while adults on land excrete mostly urea.

Uricotelic organisms, such as reptiles, birds, and many insects, convert ammonia into uric acid. Uric acid is not water-soluble, so it can be excreted as a paste or powder with very little water. It is also less toxic than urea. However, making uric acid requires even more energy than making urea. These different excretory patterns show how animals balance water use, energy cost, and habitat needs.

Nitrogen Waste in Animal Excretion

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Liver Detox and the Urea Cycle

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Animals use different excretory strategies to remove waste from the body. These strategies matter because most waste must be dissolved in water before it can leave the body. That means excretion is closely tied to water balance. Nitrogenous wastes are some of the most important animal wastes. Nitrogen is released when proteins and nucleic acids are broken down for energy or turned into carbohydrates and fats. Proteins become amino acids, and nucleic acids become nitrogenous bases. The...

what are osmoregulation and excretion?

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key terms and concepts

Explore how animals remove nitrogen waste as ammonia, urea, or uric acid, and how these excretory strategies help balance water loss and energy use.

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Nitrogen Waste in Animal Excretion

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