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Ch. 40 - Water and Electrolyte Balance in Animals
Chapter 39, Problem 9

Biologists have been able to produce mice that lack functioning genes for aquaporins. How would the urine of these mice compare to that of mice with normal aquaporins? a. lower volume and lower osmolarity b. lower volume and higher osmolarity c. higher volume and lower osmolarity d. higher volume and higher osmolarity

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Step 1: Understand the role of aquaporins. Aquaporins are proteins that form pores in the cell membrane, allowing water to move in and out of the cell. They play a crucial role in the kidney's ability to concentrate urine.
Step 2: Consider the effect of lacking aquaporins. If the mice lack functioning genes for aquaporins, their cells would be less permeable to water. This means that less water would be reabsorbed from the urine in the kidneys.
Step 3: Predict the effect on urine volume. If less water is reabsorbed, the volume of urine would be higher.
Step 4: Predict the effect on urine osmolarity. If less water is reabsorbed, the urine would be less concentrated, meaning it would have a lower osmolarity.
Step 5: Match your predictions to the answer choices. The urine of mice lacking functioning genes for aquaporins would have a higher volume and lower osmolarity, so the correct answer is (c).

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Key Concepts

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

Aquaporins

Aquaporins are specialized membrane proteins that facilitate the transport of water across cell membranes. They play a crucial role in regulating water balance in various tissues, particularly in the kidneys, where they help concentrate urine by allowing water reabsorption. Mice lacking functional aquaporins would struggle to retain water, leading to significant changes in urine composition.
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Osmolarity

Osmolarity refers to the concentration of solute particles in a solution, which affects the movement of water across membranes. In the context of urine, higher osmolarity indicates a more concentrated solution, while lower osmolarity suggests a more diluted one. The presence or absence of aquaporins directly influences the osmolarity of urine by determining how much water is reabsorbed in the kidneys.
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Urine Volume

Urine volume is the amount of liquid waste produced by the kidneys and excreted from the body. It is influenced by factors such as hydration status, solute concentration, and the functionality of renal transport mechanisms, including aquaporins. Mice without functioning aquaporins would likely produce a higher volume of urine due to their inability to reabsorb water effectively, leading to more dilute urine.
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Related Practice
Textbook Question

The chloride cells of fish gills have a high density of mitochondria. How does this characteristic relate to the functional role of chloride cells? Would you expect other epithelial cells involved in ion transport to contain large numbers of mitochondria? Explain.

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Textbook Question

Explain why mammals would not be able to produce concentrated urine if their nephrons lacked loops of Henle.

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Textbook Question

Scientists have noted that marine invertebrates tend to be osmoconformers, while freshwater invertebrates tend to be osmoregulators. Suggest an explanation for this phenomenon.

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Textbook Question

To test the hypothesis that mussels are osmoconformers, researchers exposed mussels to water of varying osmolarities and then drew hemolymph samples from the mussels. Graph the data provided here. Put the independent variable on the x--axis and the dependent variable on the y-axis. Is the researchers' hypothesis supported by the data? 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 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

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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. 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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