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Light Microscope And Electron Microscopes Essay

1192 words - 5 pages

Magnification and ResolutionMagnification is how much bigger a sample appears to be under the microscope than it is in real life.Overall magnification = Objective lens x Eyepiece lensResolution is the ability to distinguish between two points on an image.· The resolution of an image is limited by the wavelength of radiation used to view the sample.· This is because when objects in the specimen are much smaller than the wavelength of the radiation being used, they do not interrupt the waves, and so are not detected.· The wavelength of light (min. - violet is 400nm) is much larger than the wavelength of electrons, so the resolution of the light microscope is a lot lower.· The actual resolution is often half the size of the wavelength of radiation used. Thus, for the light microscope the maximum resolution is about 200nm.· In other words, if two objects in the specimen are closer than 200nm in real life, then they will only show up as one object on the image.· Using a microscope with a more powerful magnification will not increase this resolution any further. It will increase the size of the image, but objects closer than 200nm will still only be seen as one point.Light MicroscopyThe light microscope is the main tool which has been used to look at biological specimens for many years and is still very much in use today. Very small subjects, such as bacteria, can be looked at whole under a microscope, but larger tissues must first be chemically preserved, embedded in wax, sliced very thinly, mounted on glass slides and stained before viewing. Some semi-translucent specimens, such as the chick and zebrafish embryos, can be looked at whole under microscopes specially designed for this purpose. In all cases, the microscope works by light being focused by a concave mirror and/or a condenser before it passes through the specimen and into an 'objective', which magnifies the subject before it is viewed through the eyepiece. Certain components of the tissue, such as nerves or a protein, can be seen by staining them with specific dyes. Some of these are fluorescent and only show up when filters are used to block out all light except that of the same wavelength as the dye.There are other variations of light microscopy, some of which are seen in this display. In Dark Field Illumination, an opaque disc is placed above the condenser of the microscope so that light around the edge of the disc is reflected by the specimen, which appears to be on a dark background. The tissues may be further emphasised by staining, as has been done in the case of the Aspergillus fungus. Differential Interference Contrast optics is another variation which relies on polarised light being slightly bent as it passes through tissues. The differences in composition of different cells causes slight changes in the bending of the light. After the light has passed through the tissue it passes through...

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