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Stack #96661
Microscopy complete
Question | Answer |
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Key characteristics of a reliable microscope are: | Magnification – ability to enlarge objects and (Resolving) Power - ability to show detail |
Magnification in most microscopes results from interaction between | visible light waves and curvature of the lens |
the image appears enlarged | Depending on the size and curvature of the lens |
extent of enlargement | magnification |
refraction | angle of light passing through convex surface of glass changes |
power of objective X power of ocular = | total magnification |
3 Types of Light Microscopes | Bright-field, Dark-field, Phase-contrast |
most widely used microscope; specimen is darker than surrounding field; live and preserved stained specimens | Bright-field |
Microscope that uses brightly illuminated specimens surrounded by dark field; live and unstained specimens | Dark-field |
Microscope that transforms subtle changes in light waves passing through the specimen into differences in light intensity, best for observing intracellular structures | Phase-contrast |
Microscope useful in diagnosing infections | Fluorescence Microscope |
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 |
Forms an image with a beam of electrons that can be made to travel in wavelike patterns when accelerated to high speeds | Electron Microscopy |
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. |
2 Types of Electron Microscopes | Scanning electron microscopes (SEM) and (TEM) Transmission electron microscopes |
Transmission electron microscopes (TEM) | transmit electrons through the specimen. Darker areas represent thicker, denser parts and lighter areas indicate more transparent, less dense parts. |
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. |
Two types of Specimen Preparation techniques | Wet mounts and Fixed mounts |
Wet mounts | allow examination of characteristics of live cells: motility, shape, and arrangement |
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. |
Staining Dyes create contrast by | imparting a color to cells or cell parts. |
Positive staining | surfaces of microbes are negatively charged and attract basic dyes |
Negative staining | microbe repels dye, the dye stains the background |
Simple stains | one dye is used; reveals shape, size, and arrangement |
Differential stains | use a primary stain and a counterstain to distinguish cell types or parts (examples: gram stain, acid-fast stain and endospore stain) |
Special stains | reveal certain cell parts not revealed by conventional methods: capsule and flagellar stains |