Homework_8_01-26-09_C&A

Homework_8_01-26-09_C&A - Biology 5A Homework 8...

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Biology 5A Homework 8 January 26-28, 2009 1. Red blood cells circulating in the bloodstream need to take up amino acids to maintain their structure and function. This homework problem involves an experiment investigating the glutamine (Gln, an amino acid) cotransport system that transports Gln across the plasma membrane into red blood cells. A micromanipulator is a fine mechanical positioning device that can be used, together with a microscope for viewing, to insert microelectrodes and micropipets through the plasma membrane into the cytoplasm of cells. A red blood cell is impaled with a micropipet containing ATP and a microelectrode that can measure the concentration of sodium ion (see accompanying figure). At time T1, ATP is injected through the micropipet into the cytoplasm. At a later time T2, Gln is added to the solution outside the cell. The changes in sodium concentration in the cytoplasm are plotted (see accompanying graph). Which of the solid lines in the graph shows the most likely time course of changes of the cytoplasmic sodium concentration during this experiment? A. curve A B. curve B C. curve C D. curve D E. curve E (Ans. D)
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2. Human cells that are roughly spherical in shape have a diameter of about 25 micrometers. This problem will give you a sense of how big that is compared to everyday objects. Calculate how many spherical cells of 25 micrometer diameter would have to be lined up like beads on a string (see accompanying figure) to span a distance of 1 cm, which is about the same as the width of your fingernail. Recall that 1 cm = 10 -2 m, and 1 micrometer = 10 -6 m. How many cells must be lined up to span a distance of 1 cm? A. 250 cells B. 400 cells C. 2,500 cells D. 4,000 cells E. 25,000 cells (Ans. B) Problem Solution: Fingernail = 1 cm X (10 -2 m/ 1 cm) X (1 micometer/10 -6 m) X (1 cell/25 micrometer) = 400 cells 3. When you get back to your dorm room on a Sunday night, you find on your desk a half-eaten cup of soup that you had started on Friday afternoon before leaving campus for the weekend. The soup is cloudy, scumy, and smelly. Something
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Homework_8_01-26-09_C&A - Biology 5A Homework 8...

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