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Light and Electron Microscope.

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Light and Electron Microscope

  • The light microscope (like the ones commonly used in schools) relies on light being reflected onto a mirror, which shines through a very small, thin specimen. Often this will be a section through some living cells or tissue. The section must be thin enough to allow the light rays to pass through it and then onto the eye of the person using the microscope. Glass lenses focus the light rays.
  • The electron microscope is a much more powerful and expensive piece of kit. Instead of light, it uses a beam of electrons which are fired at a very thin section of material. The electrons scatter when they hit the specimen and affect a photographic plate so that a black and white image of the specimen is formed. These microscopes are harder to use, but the enable you to look at really tiny objects, even molecules.
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  • Magnification (X). This is the number of times larger an image can be made compared to the real object. A LM can achieve a magnification of 1500 x . An EM can achieve 500,000 x – 1,000,000 x.
  • Specimens. The LM passes light through a thin section of tissues and can view living material. The EM views very thin sections but must view the specimen in a vacuum and so the material will be dead. A scanning electron microscope can however view the surface of a specimen producing a complex 3D surface, without the need for thin sections.
  • Staining. The LM uses a variety of stains to show structures in different lights. EM’s use heavy metal stains to reflect and bounce electrons in the specimen.
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A vacuum means that living specimens cannot be viewed. As well as this, specimens must be very thin as the electrons  are easily scattered and would not pass through a thicker section. Heavy metals are used to stain parts of specimens. This increases the contrast between areas and gives a better picture.In a transmission  electron microscope (TEM), the electrons pass through the specimen and  are focused onto a fluorescent screen or directly onto a photographic plate. This is because the human eye cannot see electrons.                                                                                                      With a scanning electron microscope (SEM), electrons are reflected  from  the surface and  collected to form a television-like image on a screen. They give a three-dimensional image of the surface of an object.

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