42. Osmoregulation and Excretion

An albatross spending its life hovering over the ocean provides an extreme example of __________, the process by which animals control solute concentrations and balance water gain and loss.

Osmoconformers are animals that __________.

In a marine environment, animals that are isoosmotic relative to their environment __________.

Which type of organism would have the least chance of long-term survival in the given environment?

Why do freshwater fish excrete a large amount of very dilute urine?

Dehydration in animals __________.

How do aquatic birds such as the wandering albatross avoid becoming dehydrated even though they live in an environment that is almost entirely salt water?

Most of our nitrogen-containing waste products are a result of __________.

What conditions are responsible for the stimulation of the juxtaglomerular apparatus (JGA)?

Alcohol consumption increases urinary output because alcohol __________.

Secretion of ADH (antidiuretic hormone) from the __________ occurs in response to __________ and causes __________.

Most aquatic animals excrete ammonia, whereas land animals excrete urea or uric acid. What is the most likely explanation for this difference?

What is the function of antidiuretic hormone (ADH) in the body?

The loops of Henle in the kidneys of a desert kangaroo rat are much longer than those in a white laboratory rat because the __________.

At a particular position along a nephron, the osmotic potential of the filtrate is 500 mOsm/L, whereas the surrounding kidney's is 600 mOsm/L. Which of the following is a likely result?

The lowest osmotic potential inside a nephron will be found in __________.

What is the function of the ascending loop of Henle?

As filtrate passes through the long loop of Henle, salt is removed and concentrated in the interstitial fluid of the kidney medulla. Because of this high salt concentration, the nephron is able to __________.

All of the following processes occur in the nephron of the kidney except __________.

Which is an accurate pairing of a key excretory function with its definition?

Which is an accurate statement about the anatomy of the human excretory system?

Which of the following substances is generally filtered from the blood by the kidneys?

The primary nitrogen-containing compound excreted by our kidneys is __________.

Metanephridia are found in __________ and function in __________.

The fluid that enters vertebrate nephrons is called the filtrate. What is the source of the filtrate?

The most effective molecule for nitrogenous waste disposal in desert animals would be __________.

Many insects, birds, and other reptiles excrete nitrogenous wastes in the form of uric acid, which __________.

In each nephron of the kidney, the glomerulus and Bowman's capsule __________.

The bed of capillaries in a vertebrate kidney where water, urea, and salts are filtered out of the blood is the __________.

Which of the following is a function of the excretory system?

Which excretory system contains structures called flame bulbs that function in filtration?

Which of the following is filtered from blood but not normally found in urine?

The filtrate formed by the nephrons in the kidney is not urine. The filtrate is first refined and concentrated by the processes of __________, which form the urine that leaves the body.

Which of the following is the most accurate and comprehensive description of the function of kidneys?

The functional units of kidneys are __________.

Which of the following is a tube that carries urine from the kidneys to the urinary bladder in a mammal?

Unlike an earthworm's metanephridia, a mammalian nephron a. is intimately associated with a capillary network. b. functions in both osmoregulation and excretion. c. receives filtrate from blood instead of coelomic fluid. d. has a transport epithelium.

Complete this map, which presents the three main topics of this chapter.

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 process in the nephron is least selective? a. filtration b. reabsorption c. active transport d. secretion

In this schematic of urine production in a nephron, label the four processes involved and list some of the substances that are moved in each process.

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

Which of the following animals generally has the lowest volume of urine production? a. vampire bat b. salmon in fresh water c. marine bony fish d. freshwater flatworm

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 collecting duct.

The high osmolarity of the renal medulla is maintained by which of the following? (A) active transport of salt from the upper region of the descending limb. (B) the loose packing of juxtamedullary nephrons. (C) diffusion of urea into the collecting duct. (D) diffusion of salt from the descending limb of the loop of Henle

The high osmolarity of the renal medulla is maintained by all of the following except a. active transport of salt from the upper region of the ascending limb. b. the spatial arrangement of juxtamedullary nephrons. c. diffusion of urea from the collecting duct. d. diffusion of salt from the descending limb of the loop of Henle.

In each nephron of the kidney, the glomerulus and Bowman's capsule a. filter the blood and capture the filtrate. b. reabsorb water into the blood. c. break down harmful toxins and poisons. d. refine and concentrate the urine for excretion.

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

In which of the following species should natural selection favor the highest proportion of juxtamedullary nephrons? a. a river otter b. a mouse species living in a temperate broadleaf forest c. a mouse species living in a desert d. a beaver

As filtrate passes through the loop of Henle, salt is reabsorbed and concentrated in the interstitial fluid of the medulla. This high solute concentration in the medulla enables nephrons to a. excrete the maximum amount of salt. b. neutralize toxins that might be found in the kidney. c. excrete a large amount of water. d. reabsorb water from the filtrate very efficiently.

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?

African lungfish, which are often found in small stagnant pools of fresh water, produce urea as a nitrogenous waste. What is the advantage of this adaptation? a. Urea takes less energy to synthesize than ammonia. b. Small stagnant pools do not provide enough water to dilute ammonia, which is toxic. c. Urea forms an insoluble precipitate. d. Urea makes lungfish tissue hypoosmotic to the pool.

Birds and insects excrete uric acid, whereas mammals and most amphibians excrete mainly urea. What is the chief advantage of uric acid over urea as a waste product? a. Uric acid is a much simpler molecule. b. It takes less energy to make uric acid. c. Less water is required to excrete uric acid. d. More solutes are removed excreting uric acid.

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.

A freshwater fish would be expected to a. pump salt out through its gills. b. produce copious quantities of dilute urine. c. have scales and a covering of mucus that reduce water loss to the environment. d. do all of the above.

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

Match each of the following components of blood (on the left) with what happens to it as the blood is processed by the kidney (on the right). Note that each lettered choice may be used more than once. 8. Water 9. Glucose 10. Plasma protein 11. Toxins or drugs 12. Red blood cell 13. Urea a. passes into filtrate; almost all excreted in urine b. remains in blood c. passes into filtrate; mostly reabsorbed d. secreted and excreted

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; BioSkills 3). 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.

Which process in the nephron is least selective? a. secretion b. reabsorption c. filtration d. passive diffusion of salt

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.

Compare the water and salt regulation in a salmon when it swims in the ocean to when it migrates into fresh water to spawn.

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.)

Two endothermic animals are the same size, but one is a carnivore and the other is an herbivore. Predict which of these animals would produce the greatest amount of nitrogenous wastes. Explain.

Kidneys were the first organs to be transplanted successfully. A donor can live a normal life with a single kidney, making it possible for individuals to donate a kidney to an ailing relative or even an unrelated individual. In some countries, poor people sell kidneys to transplant recipients through organ brokers. What are the pros and cons associated with organ commerce?

Scientists have found that the quantity of aquaporin molecules inserted in the membranes of collecting duct cells changes in response to ADH levels. Draw a line graph proposing a relationship between ADH levels and its effect on the quantity of aquaporins. Additionally, explain how the relationship between ADH and aquaporins corresponds to situations of dehydration and hydration.