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.

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.

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