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Electron microscopy.

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Introduction

Veronica Ouyang 12C

Electron microscopy

The development of the electron microscope (EM) has had a significant impact on science research. Invented in the 1930s, the present day version of the EM can magnify up to 500,000 times and has a resolution of about 1nm. In contrast, the light microscope can magnify an object by a maximum of 1500 times and the resolving power is 200nm. That means organelles, which are only blurred images when viewed with a light microscope, can now be studied in great details. Many new structures therefore have been discovered using the EM.

Instead of using light, the EM uses a beam of electrons to resolve objects. The beam, which is produced by a heated filament, can be bent and focused by electromagnetic

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Middle

The SEMs can be used to study relatively large 3-dimentional objects. Thin sections are not required as the SEM records the electrons that are reflected off the surface of the object but the surface is coated with a thin film of gold. Although the SEM does not have the revolving power of the TEM, it is more versatile and can be used to observe many kinds of intact structures.

Tissues to be observed though the TEM are subjected to five main preparation procedures. These are:

  • Fixation—preserves the material in a life-like state using substances, which prevent enzyme action.
  • Dehydration—removes water, allowing the tissue to be penetrated by the embedding medium by using alcohol.
  • Embedding—cuts the specimen in a suitable
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Conclusion

Another problem occurs as the EM can only be used to observe dead material. This is because a vacuum is there inside the EM. Air must be removed or otherwise the electrons would be scattered in all directions by the air molecules. Nevertheless no living organism or cells can exist in a vacuum.

In conclusion, the EM has revolutionised the understanding of the structure and function of cells. However, due to the fact that it is very expensive, large, complex and has to be maintained under controlled conditions, e.g. constant temperature, as well as the mentioned drawbacks. The use of the EMs is normally limited to universities and research establishments. Light microscopes still play a major role in basic scientific observations.

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