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Thinking Scientifically
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  1. The mucus in bronchial tubes must be thin so that the cilia can function to move bacteria and viruses up into the throat away from the lungs. Which way does C1- normally move across the plasma membrane (see Fig. 5.4, top) of bronchial tube cells in order to maintain normal fluidity of the mucus? Use the concept of osmosis to explain your answer.
  2. Winter wheat is planted in the early fall, grows over the winter when the weather is colder, and is harvested in the spring. As the temperature drops from fall to winter, the makeup of the plasma membrane of winter wheat changes. Unsaturated fatty acids replace saturated fatty acids in the phospholipids of the membrane. Why would colder weather select for the different lipid makeup in the plasma membrane?

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