1.
Study the diagram of a salmon's life cycle in Figure 39.5b (page 752 in your textbook). Explain the changes that need to occur in water and electrolyte balance as an individual moves from freshwater to salt water and back. Specifically, state when the animal should drink or not drink, when cells in the gill epithelium should excrete or import electrolytes, and why each change occurs.
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2.
The chloride cells of fish gills are sometimes called mitochondria-rich cells due to their high density of mitochondria. How does high mitochondrial density relate to the functional role of chloride cells? Would you expect other epithelial cells involved in ion transport to contain high numbers of mitochondria? Explain.
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3.
Why is it significant that cells involved in transport processes often have microvilli?
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4.
This chapter introduced a number of features that help terrestrial animals reduce water loss. These traits include the layer of wax found on insect exoskeletons, the ability of insects to close the openings to their respiratory passages, secretion of nitrogenous wastes as insoluble uric acid, exceptionally long loops of Henle in the mammalian kidney, and retention of water in the nasal passages of desert mammals. Predict how each of these traits differs in animals that live in very humid versus very dry habitats. How would you test your predictions?
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5.
In insects, active transport of electrolytes into the Malpighian tubules leads to the formation of a pre-urine that is isotonic with the hemolymph. In mammals, urine formation begins with blood pressure in the renal corpuscle that leads to the formation of a fitered pre-urine that is isotonic with the blood. In insects, the pre-urine is processed in the hindgut; in mammals the pre-urine is processed in the remainder of the nephron. How are the processing steps in insects and mammals similar? How are they different?
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