sample_midterm_1_2007_key

sample_midterm_1_2007_key - YOUR NAME_ Student ID#_ MIDTERM...

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YOUR NAME__________________________ Student ID#_________________ 1 NPB 100 MIDTERM 1 SPRING, 2007 Your signature______________________ Please check this box if you do not want your exam returned in the bins in the hallway… Question Score Total 1 6 2 6 3 25 4 8 5 9 6 15 7 11 8 11 9 9 TOTAL 100
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Student ID#_________________ 2 Question 1. (6 points) 1a. (2 points) When the brain is deprived of oxygen, mitochondria inside neurons stop producing ATP. What effect does this have on the resting membrane potential of neurons? The membrane potential will rapidly depolarize about 11 mV and then more slowly depolarize up to zero mV. 1b.(4 points) Explain your answer to question 1a. Without ATP, the Na/K ATPase cannot work. This will initially remove the electrogenic effect of the pump, depolarizing the membrane potential about 11 mV. It will then over time result in a breakdown of the sodium and potassium concentration gradients until both ions are found in equal concentrations on the two sides of the membrane, at which time the membrane potential will equal 0mV. Question 2 (6 points) 2a. (2 point) A model cell has only potassium channels in its membrane. The concentration of potassium is larger inside the cell than outside. The concentration of sodium is larger outside the cell than inside. The concentration of chloride is equal inside and outside. Is the membrane potential of the cell positive or negative? Negative 2b. (4 points) Explain your answer to question 2 a. To get full credit you should include at least one equation in your answer. Because the membrane is only permeable to potassium, the membrane potential will be at the equilibrium potential for potassium. The equilibrium potential for potassium is defined by the Nernst equation EK = RT/zF (ln ([K]o/[K]i)). Since there is more potassium inside the cell than outside, ([K]o/[K]i) is less than 1, so (ln ([K]o/[K]i) is a negative number. For potassium, z = 1, so RT/zF is a positive number. Therefore the membrane potential of the cell is the multiple of a negative and a positive number, that is a negative number. GO ON TO NEXT PAGE!
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sample_midterm_1_2007_key - YOUR NAME_ Student ID#_ MIDTERM...

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