Practice exam 1 key

Practice exam 1 key - Biological Sciences 54 Exam 1 Answer...

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Biological Sciences 54 Spring 2006 Exam 1 Answer Key 1. A) 10 pts Transmission electron microscopy The tissue/sample is chemically fixed and cut into thin sections. Sections are stained with heavy metal salts such as osmium tetroxide or antibodies linked to gold particles. The stream of electrons passes evenly through unstained portions of the sample, but where the tissue is stained, the electrons are diffracted resulting in dark regions in the image collected. The images give high resolution 2D information on a section through the sample. Scanning electron microscopy The tissue/sample is also fixed, but instead of sectioning and staining certain areas of the sample with heavy metals, the sample is unsectioned and coated with a metal such as platinum. A beam of electrons is scanned over the entire surface. Scattered electrons together with secondary electrons released from the metal coating are focused onto a detector. The image has a 3D appearance and reveal the surface topography of the sample. B) 5 pts. Advantage: Electron microscopy has a resolution that is almost 10X higher than methods such as phase contrast, which depend upon visible light. Disadvantage: Samples must be fixed. So, it is not possible to follow processes in living cells/tissues.
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2. 10 pts The Na+/glucose symporter depends upon a cytoplasmic Na+ concentration that is significantly lower than that of the external environment. The Na+ gradient is the direct energy source that drives the import of glucose into epithelial cells. This process requires ATP because it is the Na+/K+ Pump that generates the required Na+ gradient, and it
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This note was uploaded on 04/07/2008 for the course MCB 54 taught by Professor Lue during the Fall '06 term at Harvard.

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Practice exam 1 key - Biological Sciences 54 Exam 1 Answer...

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