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Terrestrial arthropods, birds, and reptiles convert toxic ammonia to uric acid or the closely related compound guanine (guano). However, the conversion of ammonia to uric acid requires more energy and is much more complex than the conversion of ammonia to urea, or the excretion of ammonia as performed by fish. Based on these findings, how may the excretory system of one of the terrestrial organisms listed above change if it evolved to spend most of its time in water? a. They may evolve the ability to switch between uric acid and direct ammonia excretion. b. They would further reduce their excretion of ammonia. c. They may evolve the ability to excrete uric acid without having to dissolve it in any water. d. They would excrete higher concentrations of uric acid.

Step by step solution

01

Understand the Scenario

Identify that the question involves understanding the energy cost and complexity of converting ammonia to uric acid versus urea or direct ammonia excretion.

02

Analyze Terrestrial and Aquatic Excretion

Recognize that terrestrial arthropods, birds, and reptiles convert ammonia to uric acid to conserve water because they live on land where water might be less available.

03

Consider Aquatic Adaptations

Understand that if these organisms evolved to spend most of their time in water, they would not need to conserve water as rigorously.

04

Evaluate Options

Given their new aquatic environment, [a] they may switch between uric acid and direct ammonia excretion. Direct ammonia excretion is less energy costly and more efficient in water-rich environments.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

terrestrial arthropods

Terrestrial arthropods include insects, spiders, and crustaceans that live on land. These creatures have developed several adaptations to survive in their environment, particularly in terms of excretion. Because they live on land, they face the challenge of conserving water. Water is precious in their environment, so they can't afford to lose much of it when they eliminate waste. This leads to some interesting adaptations in their excretory systems.

ammonia excretion

Ammonia excretion is a process where organisms eliminate ammonia, a toxic by-product of protein metabolism. Aquatic animals such as fish can excrete ammonia directly into the surrounding water. This is efficient and doesn't require much energy because ammonia dissolves easily in water and can be flushed out rapidly. However, for terrestrial arthropods, birds, and reptiles, direct ammonia excretion would lead to significant water loss, which isn't ideal for their survival.

uric acid production

Uric acid production is the method terrestrial arthropods, birds, and reptiles use to deal with the challenge of conserving water. They convert toxic ammonia into uric acid, a compound that is far less toxic and can be excreted with minimal water loss. However, this process is energy-intensive. Despite the higher energy cost, uric acid crystallizes and can be excreted as a semi-solid paste, conserving valuable water resources.

energy cost in excretion

The energy cost in excretion varies depending on the method used. Direct ammonia excretion is the least energy-intensive, but it requires ample water, making it suitable for aquatic animals. Urea production, used by mammals and amphibians, requires more energy than ammonia excretion but less than uric acid production. Uric acid production involves complex biochemical pathways that consume significant energy. For terrestrial organisms, though, this energy expenditure is justified as it helps them conserve water - an essential adaptation for survival on land.