![]() Embedding: Embedding in resin, ready to be sectioned.Dehydration: Removing the water form a specimen, for example, by replacing it with ethanol.Cryofixation: Freezing the sample very rapidly to preserve its state.Chemical Fixation: Stabilising an organism/sample’s mobile macrostructure.The preparation of a sample for electron microscopy is a complex process.It has a maximum magnification of about ×100000. A Scanning Electron Microscope (SEM) produces a 3D image of a sample by ‘bouncing’ electons off and dectecting them at multiple detectors.A Transmission Electron Microscope (TEM) produces a 2D image of a thin sample, and has a maximum resolution of ×500000. There are different types of Electron Microscope. Electron Microscopes can have magnifications of ×500000. Electorns have a much lower wavelength than light (100000 times shorter in fact, at 0.004nm) which means that they can be used to produce an image with resolution as great as 0.1nm. In these circumstances, and Electron Microscope may be used. Light microscopes are great and all, but sometimes their (relatively) low magnification and resolution are insatisfactory for viewing very small things, like Organelles within cells. Samples may also be Sectioned - embedded in wax this helps with preserving structure while cutting. For example, Acetic Orcein stains DNA dark red. Samples are Stained with coloured stains that bind to certain chemicals or cell structures. Many specimens require preperation before being viewed by a light microscope, as some may not be coloured or might distort when cut. They have two eyepieces to produce a 3D stereoscopic view. Dissecting Microscopes on the other hand have a low final magnification but are useful when a large working distance between the objectives and the stage is required ( e.g. during dissection). Compound Microscopes contain several lenses and magnify a sample several hundred times. An advantage of the light microscope is that it can be used to view a variety of samples, including whole living organisms or sections of larger plants and animals. The maximum magnification of light microscopes is usually ×1500, and their maximum resolution is 200nm, due to the wavelength of light.Finally, the light passes through the Eyepiece Lens, which can also be changed to alter the magnification, and into the eye. The light then passes through the Objective Lens, which focuses it and can be changed in order to alter the magnification. Light from the Condenser Lens, and then through the Specimen where certain wavelengths are filtered to produce an image. Light Microscopes, or Optical Microscopes, as they are more correctly termed, use light and several lenses in order to magnify a sample.Image Size = Actual Size × Magnification The Light Microscope
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