Nitrogenous Waste. Ew.
- Hannah Jeoung
- Jun 7, 2019
- 3 min read
By Hannah Jeoung, Animal Biology
Have you ever been in a situation where you really have to go to the bathroom, but couldn't? Perhaps, in that predicament, you wished that humans didn't have to urinate. However, without the ability to, organisms would never be able to survive.
When nucleic acids and proteins are metabolized by the body for use, nitrogenous wastes are created in the form of ammonia (NH3). In the metabolic formation of ammonia, the amino group (NH2) is combined with a hydrogen ion. Yet, ammonia proves toxic to a lot of living beings, especially because its ion ammonium (NH4+) has the ability to interfere with oxidative phosphorylation. The process of oxidative phosphorylation is essential to creating ATP, the main energy source in biological reactions. To solve this issue, many species have developed ways to convert ammonia into less hazardous substances; and as a result, led to the creation of three main types of nitrogenous wastes: ammonia, urea, and uric acid.
The first type of nitrogenous waste is ammonia. Despite its toxicity, organisms dwelling in aquatic environments can tolerate the diluted ammonia concentrations that result from the presence of large bodies of water. In other words, the high water to ammonia ratio results in the negligible presence of the hazardous compound. Therefore, certain species such as fish find it favorable to directly excrete ammonia, which ends up conserving the most energy due to ammonia being the original form of all nitrogen waste products.
For land animals like humans, ammonia must be diluted within the body in order to safely transport nitrogenous waste. Without the presence of water, they cannot utilize it as a direct method of excretion. Instead, these organisms produce urea, which is made through combining ammonia with carbon dioxide. While this produces the desired effect of low ammonia concentrations, it also proves expensive in energy during the metabolic processes that create urea.
Finally, uric acid is produced by organisms such as insects and birds. It is nontoxic and can be excreted with low levels of water loss, usually forming a type of paste. For instance, bird droppings (guano) are made of a mix of brown feces and white uric acid. On the downside, it requires even more ATP to produce.
While reasonable assumptions can be made as to what type of organism produces which type of nitrogenous waste, certain exceptions and oddities still exist. For one, some animals switch between producing mainly ammonia to urea as they develop, mainly because they switch their living habitats from aquatic to terrestrial. In addition, the type of egg that an organism is encased in may determine its ability to produce different types of nitrogenous wastes. Amphibian eggs, which have high solubility, make it ideal for the embryo to produce ammonia. On the other hand, reptilian and avian eggs have more impermeable shells, which makes soluble wastes such as ammonia dangerous to accumulate. Uric acid proves a fit alternative when considering that it can be stored as a harmless solid.
Despite the fact that land animals tend to produce mostly urea, they also excrete uric acid in small amounts as an antioxidant. Certain diseases can interrupt this process. For instance, gout is a disease that forms when there are large deposits of uric acid crystals in the body, usually through poor lifestyle and diet choices. Symptoms include joint inflammation, swelling, and kidney stones, as well as an increased risk for diabetes and heart conditions.
Now - back to our universal dilemma. A key aspect to less bathroom breaks can lie in the positive correlation between food ingested and amounts of nitrogenous waste. High energy users, such as carnivores, typically eat more than herbivores; and as a result, have to frequently excrete wastes. But as we've learned before, chronic diseases such as gout can result from poor diet choices that could arise from attempting to regulate urea output.
Maybe it is better to suffer through these small problems.
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Sources:
Urry, Lisa, et al. Campbell Biology, 11th Ed. New York, NY, Pearson Publishing Company, 2017.
Photos are linked to sources.
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