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Ch. 40 - Water and Electrolyte Balance in Animals
All textbooksFreeman 8th EditionCh. 40 - Water and Electrolyte Balance in AnimalsProblem 15
Chapter 39, Problem 15

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. True or false: Water moves by osmosis across a fish's gills to an area with a higher sodium ion concentration because water molecules are attracted to the sodium ions.

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Identify the concept of osmosis: Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.
Understand the role of gills: Fish gills function as semipermeable membranes where exchange of gases and some ions occurs, but they are not primarily involved in osmosis of water.
Analyze the statement: The statement suggests that water moves to an area of higher sodium ion concentration due to attraction to sodium ions. However, osmosis depends on solute concentration differences, not direct attraction to specific ions.
Evaluate the statement's accuracy: The statement is false because osmosis involves movement of water due to overall solute concentration differences across a membrane, not due to attraction to specific types of ions like sodium.
Conclusion: The correct understanding is that water moves by osmosis from an area of lower overall solute concentration to an area of higher overall solute concentration, irrespective of the type of ions present.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Osmosis

Osmosis is the movement of water molecules across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration. In biological systems, this process is crucial for maintaining cellular homeostasis. In the context of fish, osmosis helps regulate the internal environment by balancing the concentration of ions and water in their bodies.
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Gills and Ion Regulation

Fish gills are specialized organs that facilitate gas exchange and play a vital role in ion regulation. They allow fish to absorb oxygen from water while also managing the concentration of ions, such as sodium and chloride, in their bodies. The gills actively transport ions to maintain osmotic balance, which is essential for the fish's survival in varying water conditions.
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Sodium Ion Concentration

Sodium ions (Na+) are essential for various physiological processes in aquatic organisms, including nerve function and osmoregulation. In freshwater environments, fish must actively uptake sodium ions to counteract the natural tendency of water to dilute their internal ion concentration. The presence of higher sodium ion concentrations in the surrounding water can influence the movement of water through osmosis, impacting the fish's overall health and survival.
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Related Practice
Textbook Question

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. In a laboratory, scientists exposed freshwater bony fish (Prochilodus lineatus) to water with a high level of aluminum and compared their blood osmolarity to that of fish exposed to water with a normal aluminum level (control). The results of the experiment are shown here (asterisks indicate P<0.05 between control and treated groups at a given time; BioSkills 3). Do the data support the hypothesis that aluminum interferes with osmoregulation in freshwater fishes? Explain.

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Textbook Question

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. Why did the scientists do this experiment in a laboratory instead of simply collecting fish from a river with a high aluminum level and documenting their osmoregulatory ability?

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Textbook Question

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. The scientists also measured the activity of Na+/K+-ATPase, in the gills of the fish exposed to aluminum and compared it to that of the control fish. What do you suppose were their results? Explain.

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Textbook Question

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. Draw a graph similar to the one here showing how the results would be different if the experiment had been performed on marine bony fish in seawater. (Assume that the osmolarity of seawater is 1100 mOsm and the set point osmolarity of marine bony fishes is 290 mOsm.)

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