Which of the following statements regarding fishes that live in fresh-water is/are correct? Select True or False for each statement.

T/F Water moves across the gills via osmosis until equilibrium is established, at which time the water molecules stop moving.

T/F They lose water to their environment primarily through the gills. They replace this water by drinking.

T/F Water enters epithelial cells in their gills via osmosis. Electrolytes leave the same cells via diffusion.

T/F They have specialized epithelia that actively pump electrolytes from the environment into the blood.

Which of the following organisms would lose the most water by osmosis across its gills?

a. Marine bony fish

b. Shark

c. Freshwater fish

d. Freshwater invertebrate

What effect does antidiuretic hormone (ADH) have on the nephron?

a. It increases the water permeability of the descending limb of the loop of Henle.

b. It decreases the water permeability of the descending limb of the loop of Henle.

c. It increases the water permeability of the collecting duct.

d. It decreases the water permeability of the collecting duct.

In Gila monsters, the organ in which water from urine is reabsorbed into the bloodstream is the___________.             .

Compare and contrast the types of nitrogenous wastes excreted by animals. Identify which type can be excreted with the least water, which is most toxic, and which waste is excreted by bony fishes, by mammals, and by insects. Which type would you expect to be produced by embryos inside eggs laid on land?

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.

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

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

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

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.

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

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).

Do the data support the hypothesis that aluminum interferes with osmoregulation in freshwater fishes? Explain.

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?

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.

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.

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.)