Chapter 40 Questions

c) Higher volume and lower osmolarity. Without aquaporins in the collecting duct, water cannot be reasborbed, which would result in increased urine volume and decreased urine osmolarity.

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

1) Uric acid has very low solubility in water and can be excreted without much water loss. 2) When electrolytes are reabsorbed in the hindgut epithelium, water follows along an osmotic gradient.

CYU: Explain how the following traits are involved in water retention in insects: 1. Excretion of nitrogenous waste in the form of uric acid. 2. Selective reabsorption of electrolytes in the hindgut.

marine cartilaginous fishes osmoconform, so they do not lose water to their environment. As a result, they do not need to drink seawater, so they do not absorb as much NaCl from drinking. However, they must expend energy to make proteins that protect their cells from toxic effects of maintaining high urea concentrations in their tissues. Marine bony fishes osmoregulate, so they do not need to make those proteins. However, they must drink seawater, which increases the amount they absorb, so they must expend energy to excrete NaCl.

CYU: List the advantages and disadvantages of osmoregulating and osmoconforming in a marine environment.

Water intake leads to lowered

CYU: Predict how the following events would affect urine production: drinking massive amounts of water, eating large amounts of salt, and refraining from drinking water for 48 hours.

Ammonia is the most toxic and must be diluted with large amounts of water to be excreted safely. Urea and Uric acid are less toxic and do not have to be excreted with the least water. Bony fishes excrete ammonia; mammals excrete urea; and insects excrete uric acid. You would expect the embryos inside terrestrial eggs to produce uric acid, since it is the least toxic and has very low solubility in water.

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?

Ethanol inhibits water reabsorption, leading to a larger volume of less concentrated urine. Nicotine increases water reabsorption, leading to a smaller volume of more concentrated urine.

If you understand ADH's effect on the collecting duct, you should be able to predict how urine formation is affected by ethanol, which inhibits ADH release, and by nicotine, which stimulates ADH release.

In step 1, the Na+/K+ -ATPase performs primary active transport. In step 2, the Na+ -dependent cotransporters perform secondary active transport. In steps 3 and 4, solutes and water moves via facilitated diffusion. Simple diffusion does not occur here.

If you understand the concept, you should be able to assign one of the following transport mechanisms to each of the four steps above: simple diffusion, facilitated diffusion, primary active transport, secondary active transport.

Marine animals face dehydration because the high osmolarity of seawater causes them to lose water by osmosis. Terrestrial animals face dehydration because they constantly lose water to the air via evaporation from their body surfaces.

If you understand this concept, you should be able to explain why maintaining water and electrolytes homeostasis poses similar challenges to marine and terrestrial animals.

1) Less water will be reabsorbed because the osmotic gradient in the interstitial fluid will not be as steep. 2) Filtrate osmolarity will be lower because less water will have been reabsorbed. 3) Salt reabsorption will be reduced because the concentration of NaCl in the filtrate will be lower.

If you understand this concept, you should be able to predict what happens to the osmotic gradient when the drug furosemide inhibits membrane proteins that pump sodium and chloride ions out of the thick ascending limb. Specifically, how does this drug affect (1) water reabsorption in the descending limbs, (2) the osmolarity of the filtrate at the bottom of the loop of Henle, and (3) reabsorption of salt in the thin ascending limb?

Freshwater has such a low osmolarity that if invertebrates osmoconformed to it the ion concentration in their interstitial fluid would be too low to conduct electrical currents in their excitable tissues.

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

Mitochondria produces ATP in cellular respiration. A key component of salt transport by chloride cells is Na+/K+ -ATPase, which requires ATP to function. Because ATP fuels establishment of the ion gradients necessary for the cotransport mechanisms used by chloride cells as well as other epithelial cells involved in ion transport, an abundance of mitochondria would be expected in these cells.

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.

The activity of Na+/K+ -ATPase was lower in the aluminum-treated fish than in the control fish. As a result, less sodium was imported from the water by active transport, leading to the observed reduction in blood osmolarity.

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.

The hypothesis that the mussels are osmoconformers is supported because the osmolarity of their hemolymph is very close to the wide range of osmolarities of the water to which they were exposed.

To test the hypothesis the mussels are osmoconformers, researchers exposed mussels to water of varying osmolarities and then drew hemolymph samples from the mussels. Graph the data below. 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.

False. Water moves by osmosis because there is a net diffusion of water molecules from solution of low osmolarity to solutions of high osmolarity, not because water molecules are attracted to ions like sodium.

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

c) It increases water permeability of the collecting duct

What effect does antidiuretic hormone (ADH) have on the nephron? a) It increases water permeability of the descending limb of the loop of Henle. b) It decreases water permeability of the descending limb of the loop of Henle. c) It increases water permeability of the collecting duct. d) It decreases water permeability of the collectig duct.

Carrying a large amount of water in the bladder may be energetically costly to the animal. The animal also might not be able to run as quickly and therefore might have an increased predation risk.

What physiological trade-offs might be imposed by carrying a large amount of water in the bladder?

a) Diffusion of sodium out of the body

Which of the following is an osmoregulatory challenge that freshwater fishes need to overcome? a) Diffusion of sodium out of the body b) Diffusion of water out of the body c) Active transport of sodium out of the body d) Active transport of water of the body

a) marine body fish

Which of the following organisms would lose the most water by osmosis across its gills? a) marine body fish b) shark c) freshwater fish d) freshwater invertebrates

Without loops of Henle, there would be no concentration gradient in the interstitial fluid of the kidney's medulla, so water could not be absorbed from the pre-urine in the collecting duct; as a result, concentrated urine could not be formed.

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

bladder

Fill in the blank: In Gilla monsters, the organ in which water from urine is reabsorbed into the bloodstream is the _____________________.

Yes, the data support the hypothesis because the blood osmolarity of the aluminum-treated fish dropped between 6 hours and 24 hours after aluminum exposure began, whereas the blood osmolarity of the control fish did not change during that period

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

The cuticle would likely have the most wax in the summer, when hot, dry weather would accelerate evaporation from the body surface.

In what season would a desert insect's cuticle likely have the most wax? Explain.

c) water enters epithelial cells in their gills via osmosis. Electrolytes leave the same cells via diffusion.

Which of the following statements is true of the fishes that live in freshwater? a) Water moves across the gills via osmosis until equilibrium is established, at which time the water molecules stop moving. b) They lose water to their environment primarily through the gills. They replace this water by drinking. c) Water enters epithelial cells in their gills via osmosis. Electrolytes leave the same cells via diffusion. d) They have specialized epithelia that actively pump Na+ and Cl- from the blood into their environment.

The researchers did a laboratory study to establish cause and effect by comparing two groups (the aluminum-treated fish and the control fish) that differed in only one variable (the aluminum content of the water). If they had simply sampled fish from water polluted with aluminum, they could not have attributed any observed effects on osmoregulation to aluminum with certainty because there would have been uncontrolled variables.

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