bis_104_mid_i_exam_key_b08 - Page 3

bis_104_mid_i_exam_key_b08 - Page 3 - Explain your answer....

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1. In your research lab you have a microscope with the following specifications: An ocular lens (eyepiece) capable of 10x magnification. An objective lens (oil immersion) with a numerical aperture (NA) of 1.2 and capable of 100x mag. A light source with an average wavelength output of 520 nm. Calculate the resolving power of this microscope. (4) d = resolution = (0.61) (lamda nm) / numerical aperture = (0.61) (520 nm) / 1.2 = 264 nm 2. Suppose you were examining a sample of endothelial cells (cell dia. = 20 um) and checking the sample for possible contamination by the bacterium S. aureus (spherical dia = 1.0 um,). If there were two bacteria sitting next to each other and separated by 0.5 um, does your microscope have the magnifying power and resolving power to allow you to see these two bacteria as distinct entities, or would they appear as one object?
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Unformatted text preview: Explain your answer. (2) Yes. Mag = (10x) x (100x) = 1,000x. Since the bacteria are 1.0 um diameter they can be seen at this mag. And, since the microscope resolution maximum is 264 nm (i.e., less than 500 nm) they can be detected as two separate entities. 3. What two light microscopy procedures or techniques could you use to improve the visibility of the cells and bacteria specimen described above? (2) a) Stain the specimen with chemical dyes to create contrast. b) Use phase-contrast or DIC microscopy to achieve contrast. 4. What is meant by the term “ empty magnification ”? (2) Magnification that gives a larger image without improving the resolution. . ( Magnification beyond the resolving power of a scope). Page 3 Name _______________________________ Demo...
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This note was uploaded on 05/24/2010 for the course BIS 104 taught by Professor Scholey during the Spring '08 term at UC Davis.

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