Fish and other aquatic organisms are exposed to many types of water pollutants, including metals such as aluminum. Although a low level of aluminum is found in unpolluted water, many lakes and streams have an increased level because of mining, sewage treatment, and accidental spills of toxic materials. Aluminum pollution can result in mass fish die-offs such as the one pictured here. How does this occur? Which of the following is an osmoregulatory challenge that freshwater fishes need to overcome? a. diffusion of sodium ions out of the body b. diffusion of water out of the body c. active transport of sodium ions out of the body d. active transport of water out of the body

Verified step by step guidance

1. Step 1: Understand the problem. The question is asking about the osmoregulatory challenges that freshwater fishes face. Osmoregulation is the process by which organisms regulate the osmotic pressure of their body fluids to maintain the homeostasis of their body's water content. Fish, like other aquatic organisms, need to balance the concentration of salts and water in their bodies with that of their environment.
2. Step 2: Review the options. Option a suggests that the diffusion of sodium ions out of the body is a challenge. Option b suggests that the diffusion of water out of the body is a challenge. Option c suggests that the active transport of sodium ions out of the body is a challenge. Option d suggests that the active transport of water out of the body is a challenge.
3. Step 3: Recall that freshwater fishes live in an environment where the concentration of salts is lower than in their body fluids. Therefore, they face the challenge of water constantly diffusing into their bodies (due to osmosis) and salts diffusing out of their bodies.
4. Step 4: Based on this understanding, we can eliminate options b and d because freshwater fishes do not face the challenge of water or salts being actively transported out of their bodies. They actually need to actively take in salts to compensate for what is lost through diffusion.
5. Step 5: Therefore, the correct answer is option a: diffusion of sodium ions out of the body. This is a challenge that freshwater fishes need to overcome in order to maintain the balance of salts and water in their bodies.

Key Concepts

Osmoregulation

Osmoregulation is the process by which organisms regulate the balance of water and solutes in their bodies to maintain homeostasis. In freshwater fish, this involves managing the influx of water from their environment, as they are constantly gaining water due to osmosis. To counteract this, they must excrete excess water while retaining essential ions, primarily sodium and chloride, to ensure proper cellular function.

Diffusion

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. In the context of freshwater fish, diffusion plays a critical role in the movement of ions and water across their gills and skin. Understanding how diffusion affects the concentration of sodium ions and water in fish is essential for grasping the osmoregulatory challenges they face in a dilute environment.

Active Transport

Active transport is the process by which cells move ions or molecules against their concentration gradient, requiring energy, typically in the form of ATP. For freshwater fish, active transport is crucial for retaining sodium ions, which are lost to the surrounding water through diffusion. This mechanism allows fish to maintain the necessary ion balance in their bodies, despite the constant influx of water.