Microscopy complete
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| Key characteristics of a reliable microscope are: | Magnification – ability to enlarge objects and (Resolving) Power - ability to show detail
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| Magnification in most microscopes results from interaction between | visible light waves and curvature of the lens
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| the image appears enlarged | Depending on the size and curvature of the lens
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| extent of enlargement | magnification
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| refraction | angle of light passing through convex surface of glass changes
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| power of objective X power of ocular = | total magnification
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| 3 Types of Light Microscopes | Bright-field, Dark-field, Phase-contrast
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| most widely used microscope; specimen is darker than surrounding field; live and preserved stained specimens | Bright-field
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| Microscope that uses brightly illuminated specimens surrounded by dark field; live and unstained specimens | Dark-field
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| Microscope that transforms subtle changes in light waves passing through the specimen into differences in light intensity, best for observing intracellular structures | Phase-contrast
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| Microscope useful in diagnosing infections | Fluorescence Microscope
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| Fluorescence Microscope | Modified compound microscope with an ultraviolet radiation source and a filter that protects the viewer’s eye; Uses dyes that emit visible light when bombarded with shorter UV rays - fluorescence
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| Forms an image with a beam of electrons that can be made to travel in wavelike patterns when accelerated to high speeds | Electron Microscopy
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| Electron Microscopy | Magnification between 5,000X and 1,000,000X; Electrons have tremendous power to resolve minute structures because resolving power is a function of wavelength.
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| 2 Types of Electron Microscopes | Scanning electron microscopes (SEM) and (TEM) Transmission electron microscopes
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| Transmission electron microscopes (TEM) | transmit electrons through the specimen. Darker areas represent thicker, denser parts and lighter areas indicate more transparent, less dense parts.
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| Scanning electron microscopes (SEM) | provide detailed three-dimensional view. SEM bombards surface of a whole, METAL-COATED SPECIMEN with electrons while scanning back and forth over it.
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| Two types of Specimen Preparation techniques | Wet mounts and Fixed mounts
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| Wet mounts | allow examination of characteristics of live cells: motility, shape, and arrangement
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| Fixed mounts | are made by drying and heating a film of specimen. This smear is stained using dyes to permit visualization of cells or cell parts.
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| Staining Dyes create contrast by | imparting a color to cells or cell parts.
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| Positive staining | surfaces of microbes are negatively charged and attract basic dyes
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| Negative staining | microbe repels dye, the dye stains the background
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| Simple stains | one dye is used; reveals shape, size, and arrangement
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| Differential stains | use a primary stain and a counterstain to distinguish cell types or parts (examples: gram stain, acid-fast stain and endospore stain)
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| Special stains | reveal certain cell parts not revealed by conventional methods: capsule and flagellar stains
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