chapt02 - 2 Microscopy CHAPTER OVERVIEW This chapter...

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2 Microscopy CHAPTER OVERVIEW This chapter provides a relatively detailed description of the bright-field microscope and its use. Other common types of light microscopes are also described. Following this, various procedures for the preparation and staining of specimens are introduced. The chapter continues with a description of the two major types of electron microscopes and the procedures associated with their use. It concludes with descriptions of recent advances in microscopy: electron cryotomography and scanning probe microscopy. CHAPTER OBJECTIVES After reading this chapter you should be able to: describe how lenses bend light rays to produce enlarged images of small objects describe the various parts of the light microscope and how each part contributes to the functioning of the microscope describe the preparation and simple staining of specimens for observation with the light microscope describe the Gram-staining procedure and how it is used to categorize bacteria describe the basis for the various staining procedures used to visualize specific structures associated with microorganisms compare the operation of the transmission and scanning electron microscopes with each other and with light microscopes describe dark-field microscopy, phase-contrast microscopy, differential interference contrast microscopy, confocal microscopy, electron cryotomography, and scanning probe microscopy compare and contrast light microscopes, electron microscopes, confocal microscopes, and scanning probe microscopes in terms of their resolution, the types of specimens that can be examined, and the images produced CHAPTER OUTLINE I.Lenses and the Bending of Light A. Light is refracted (bent) when passing from one medium to another; the refractive index is a measure of how greatly a substance slows the velocity of light; the direction and magnitude of refraction is determined by the refractive indexes of the two media forming the interface B. Convex lenses bend parallel light rays from a distant light source and focus the light rays at a specific place known as the focal point; the distance between the center of the lens and the focal point is the focal length; convex lenses allow our eyes to focus at a much closer range II.Light Microscopes A. The bright-field microscope produces a dark image against a brighter background; the total magnification of the image is the product of the magnification of the objective lens and the magnification of the ocular (eyepiece) lens B. Microscope Resolution 1. Microscope resolution refers to the ability of a lens to separate or distinguish between small objects that are close together 2. The major factor determining resolution is the wavelength of light used; the shorter the wavelength, the greater the resolution 3. The numerical aperture of the objective lens (ability to gather light) also impacts resolution; the larger the numerical aperture, the greater the resolution and the shorter the working distance of the lens 9
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4. The unaided eye has a resolution of 0.2 mm; the typical light microscope has
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This note was uploaded on 05/02/2011 for the course BIOL 2051 taught by Professor Brininstool during the Spring '07 term at LSU.

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chapt02 - 2 Microscopy CHAPTER OVERVIEW This chapter...

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