Chapter 40

Which of the following statements is true of 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 \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) from the blood into their environment.

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 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.

Fill in the blank: 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 they 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 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. $$\begin{array}{cc} \begin{array}{c} \text { Water 0smolarity } \\ \text { (milliosmol/L) } \end{array} & \begin{array}{c} \text { Hemolymph 0smolarity } \\ \text { (milliosmol/L) } \end{array} \\ \hline 250 & 261 \\ 500 & 503 \\ 750 & 746 \\ 1000 & 992 \\ \hline \end{array}$$

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 out of the body

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.