1. Environmental signals alter the behavior of target cells.
a. How would you modify this definition to be consistent with Figure 20.1? Why?
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b. What makes a target cell sensitive to a particular environmental signal?
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c. Why is the term behavior a good one to use in the definition of an environmental signal? Give examples of change in behavior of the target cell, the organ, or the organism.
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d. When is the environmental signal insulin present? When is an environment signal like a neurotransmitter substance released?
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2. Considering the function of the pancreas:
a. If the pancreas is removed from an animal, what substance would you expect to find in the urine? Why?
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b. Would your findings support the contention that the pancreas is the source of insulin? What do they prove?
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c. How would you prove that insulin lowers blood sugar?
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d. Once you have shown that insulin lowers blood sugar, do your findings in question 2a support the belief that the pancreas is the source of insulin? Why?
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