Problem 6 - Campbell Biology

Question

African lungfish, which are often found in small stagnant pools of fresh water, produce urea as a nitrogenous waste. What is the advantage of this adaptation? \begin{equation}\begin{array}{l}{\text { (A) Urea takes less energy to synthesize than ammonia. }} \\ {\text { (B) Small stagnant pools do not provide enough water to dilute }} \\ {\text { ammonia, which is toxic. }} \\\ {\text { (C) Urea forms an insoluble precipitate. }} \\ {\text { (D) Urea makes lungfish tissue hypoosmotic to the pool. }}\end{array}\end{equation}

Step-by-Step Solution

Answer

The advantage is that small stagnant pools do not provide enough water to dilute ammonia, which is toxic.

Step 1: Understand the Context

Lungfish live in small, stagnant pools of freshwater where water availability is limited. They produce urea as their nitrogenous waste.

Step 2: Evaluate Answer Choice A

Consider that urea does not necessarily take less energy to synthesize than ammonia; it often requires more energy.

Step 3: Evaluate Answer Choice B

Examine if small stagnant pools lack sufficient water to dilute toxic ammonia. Since ammonia is highly toxic and needs ample water for dilution, this answer is plausible.

Step 4: Evaluate Answer Choice C

Determine if urea forms an insoluble precipitate. Urea is actually highly soluble in water, so this statement is incorrect.

Step 5: Evaluate Answer Choice D

Analyze whether urea makes lungfish tissue hypoosmotic to the pool. This is not the typical function or advantage of producing urea.

Step 6: Select the Correct Answer

Based on the evaluations, option B is the most logical. Small stagnant pools do not provide enough water to dilute ammonia, which is toxic. Urea, being less toxic, is advantageous in such environments.

Key Concepts

Nitrogenous Waste

Nitrogenous waste is a byproduct of protein metabolism in living organisms. Aquatic animals, like the African lungfish, need to excrete nitrogen waste to avoid toxicity. This waste can come in different forms depending on the animal and its habitat. Common forms include ammonia, uric acid, and urea. Each form has specific properties and is more suitable for certain environmental conditions. For aquatic life, efficient nitrogenous waste management is crucial for survival, especially in water-limited environments.

Urea vs. Ammonia

Different aquatic animals excrete nitrogenous waste in various forms based on their environmental needs.

• Ammonia: Easily produced with minimal energy expenditure but highly toxic. It needs a large amount of water to dilute and remove efficiently.


• Urea: Less toxic compared to ammonia and requires less water to be safely excreted. However, it's more energy-intensive to produce. Lungfish opt for urea production since it is safer in water-limited environments like stagnant pools.

The choice between urea and ammonia as a waste form highlights how organisms adapt to their habitats to ensure their survival and minimize toxicity.

Survival in Stagnant Water

Lungfish are an extraordinary example of adaptation to harsh environments. Stagnant water bodies have limited water flow and oxygen levels, making waste management a critical survival challenge.

• Oxygen Scarcity: Limited oxygen necessitates efficient waste management to avoid toxic build-up.


• Water Scarcity: Stagnant pools don't provide abundant water to dilute toxic wastes like ammonia. Hence, lungfish produce urea, which is less toxic and easier to excrete in smaller water volumes.

Such adaptations demonstrate the lungfish's evolutionary strategies to maintain homeostasis and thrive even in challenging environments.