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Microbiology Lect 3
Microbiology Lecture 3
| Question | Answer |
|---|---|
| Light Microscope (1,000x magnification) | - uses primary illumination source - 4 types: bright field, dark field, fluoresence, phase contrast |
| Bright Field Microscope Components | - compound microscope (2 lenses) - consists of: ocular lens, nosepeice, iris diaphram (location in the condenser, controls the amount of light leaving the condenser) - light intensity is controlled by adjusting the voltage of the light source |
| Total magnification | - total magnification = magnification of ocular lens x objective lens |
| Objective lens must be free of... | ...spherical (focusing light rays poorly) and chromatic (produced colored fringe around specimen) aberrations |
| Resolving power, resolution | - ability of a microscope to distinguish closely spaced objects as separate entities. 0.2 micrometers is the resolving power of the light microscope |
| Refractive index | - the medium through which the object is viewed, airt, water, oil |
| Dark Field Microscope (1,000-2,000x magnification) | -Useful with small think structures like flagella -Specimen appears light against a dark background -Developed by placing an opaque disk (dark field stop) in the center of the condenser. No light enters objective, specimen viewed buy scattered light |
| Phase Contrast Microscope (1,500x + magnification) | -devised by Zericke -detects small differences in refractive indices of the specimen and the surrounding background -living, unstained specimen, 3D view of specimen, specimen is illuminated w/a ring of light |
| Fluorescence Microscope (1,500x + magnification) | - fluorescence occurs when materials absorb short wavelengths of UV light and then emit light of longer wavelengths - Fluorescent dyes are used and conjugated to antibodies to identify speciemens - living, unstained specimens |
| Electron Microscope | - resolving power of 0.001 micrometers, magnification of 100,000x or greater. TEM and SEM - the electrons substitutes for the light in a conventional microscope and the beams of electrons are 100,000x shorter than the wavelengths of visible light |
| TEM | - specimens for examination are fixed and embedded in a supporting plastic resin for slicing of specimens and examination |
| SEM | - Produces a 3D image of specimen. The specimen is prepared using critical point drying, dehydrated in ethanol then placed in a chamber with Freon gas. The dehydrated specimen is coated with a thin layer of metal and viewed |
| Other Electron Microscopes | -scanning tunneling microscope: image DNA and proteins -atomic force microscope: image viruses and RBCs |
Created by:
clewis3
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