bisc307_exam_spring_05 - First Exam Answers BISC 307L -...

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1 First Exam Answers BISC 307L - General Physiology February 7, 2005 NOTE: The given answers for the subjective questions are not the only ones possible. Grading for each of the subjective questions is done relative to other students’ answers, by one TA who applies uniform criteria. 1. Which one of the following is an example of positive feedback? (c) a. The presence of acidic stomach contents in the small intestine stimulates release of the hormone secretin, which causes the pancreas to secrete an alkaline fluid into the small intestine. b. Elevated body temperature during exercise stimulates secretion of sweat glands in the skin, which leads to evaporative cooling. c. Stretching of the cervix by the baby’s head causes the posterior pituitary to release oxytocin, which stimulates contraction of uterine muscles. d. A drop in blood pH stimulates H + excretion by the kidney, to produce acidic urine. 2. A physiological ecologist was interested in studying possible seasonal changes in membrane lipids in freshwater fish. She was particularly interested in the amount of oleic acid (an 18-C monounsaturated fatty acid) relative to the amount of stearic acid (an 18-C saturated fatty acid) in membrane phospholipids. With the onset of winter, would you expect that the ratio of oleic acid to stearic acid, namely [oleic acid] / [stearic acid], to increase, decrease, or stay the same in these fish? Briefly explain your answer. ANS: You would expect the ratio to increase, due to an increase in [oleic acid], a decrease in [stearic acid], or both. Winter brings colder temperatures, which would decrease the fluidity of cell membranes and impair cellular function. Changing the fatty acid composition of the membrane phospholipids by introducing more unsaturation (-C=C-) would increase membrane fluidity to compensate 3. Which of the following statements comparing a 1 M NaCl solution and a 2 M glucose solution is most correct? (a) a. The NaCl solution is isotonic compared to the glucose solution. b. The NaCl solution is hypertonic compared to the glucose solution. c. The glucose solution has a higher osmotic pressure than the NaCl solution.
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This note was uploaded on 05/03/2010 for the course BISC 307L taught by Professor Herrera during the Spring '08 term at USC.

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bisc307_exam_spring_05 - First Exam Answers BISC 307L -...

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