1.
Examine Figure 39.14b (page 761 in your textbook) again, and note that the blood vessel that runs along the mammalian nephron is arranged so that blood flows in a countercurrent arrangement relative to the flow of fluid in the loop of Henle. Recall that the water and electrolytes that leave the loop of Henle and collecting duct diffuse into this blood vessel and are returned to the body. Why is the countercurrent arrangement for blood flow important?
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2.
You have isolated a segment of a rat nephron and introduced a solution of known composition. When you compare the fluid collected at the end of the segment with the test solution introduced at the beginning, you find that the volume has decreased by 30 percent, the Na concentration has decreased by 30 percent, but the urea concentration has increased by 50 percent. What processes in this segment might account for these changes?
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3.
According to the data reviewed in Chapter 24, the first animals that appear in the fossil record lived in marine habitats. What changes occurred in the regulation of water and electrolyte balance in animal populations that first began to occupy freshwater and terrestrial habitats? Why would natural selection favor these changes?
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4.
In some areas of the world, highway maintenance crews make extensive use of salt to keep roads free of ice in winter. Biologists are concerned about the effect of this salt on terrestrial and freshwater organisms. Why?
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5.
Ethanol is the active ingredient in alcoholic beverages. One of its many toxic effects is to inhibit the release of antidiuretic hormone (ADH) by the brain. How does the ingestion of ethanol affect urine formation? Why do people who ingest large amounts of ethanol suffer from headache, body ache, and other symptoms of dehydration?
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