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How the transmission and scanning electron microscopes work?

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How the transmission and scanning electron microscopes?


Electron microscopy is an important tool in biology in general and cellular biology in particular. The two most important types of electron microscopes are the Transmission Electron Microscope (T.E.M.) and the Scanning Electron Microscope. (S.E.M.) these two types of microscopes are both used in medical, biological and material research, and both have advantages and disadvantages over each other, which I will be mentioning in this essay.    

The transmission electron microscopes (T.E.M.)

The preparation for the T.E.M.  

Firstly the specimen is fixed, in other word it is preserved in as close to its living state as possible. The specimen then has to be dehydrated with an alcohol (e.g. ethanol). This is because the T.E.M. operates under a high vacuum and it is therefore no water should be to enter the microscope, to prevent this to happen the specimen is placed in liquid resin (similar to araldite glue).

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  • The T.E.M. is used for looking at the structure within the specimen in fine detail, which is also known as ultrastructure.
  • The ability to see the ultrastructure enables us to see the cellular organelles in detail.
  • We can quantify changes in the ultrastructure within the cells (for example after a certain treatment). This method is called morphometric analysis.
  • Morphometric analysis is carried out by taking images with a digital camera. These images are then analysed on a computer to measure the changes of the organelles within a cell.
  • The T.E.M. can also be used to see specific proteins in a cell. This is done by a method called immunogold labelling.

The scanning electron microscopes (S.E.M.)

The preparation for the S.E.M.

Firstly the specimen has to be fixed; it’s then dehydrated with an alcohol (e.g. ethanol). This is done because the electron

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Next the sample is fractured and a carbon template is made out of it using a microtome knife. Cells will then split along the path of least resistance, forming what is known as the fracture plane. The things that can cause the changes to the fracture plane are, elevation, depression, and ridges, which are cellular organelles. A heavy metal is then placed on the fracture surface at an angle, so that a shadow is produced on the surface, which enhances the contours. Finally a solid uniform layer of carbon covers the sample over the top, producing a carbon replica template of the cellular constituents, which is viewed under the microscope. The remains of the sample are no longer needed and are thrown away. Below are some pictures of different cells or organelles.



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