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Electron Microscopy and the study of the Cell.

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Electron Microscopy.

Electron Microscopes have revolutionised today’s understanding of the cell.  In 1838 Scheleiden, a botanist theorised that the basic unit of a plant was a cell, the following year the scientist Schwann came up with a similar hypothesis this time related to animal cells, their combined ideas gave us the cell theory, the idea that all living things were made from similar building blocks, cells.  It took 100 years before this idea was confirmed with the invention of the electron microscope.  Prior to this light microscopes, which enable us to see large cells, were used; but their resolving power was not high enough to confirm that all living things were made from cells as the physics of a light microscope only enables it to magnify something by about 2000x, a resolution of about 0.2 micrometers.  In this essay I will be discussing the uses of electron microscopes, the way in which they are used and also comparing the electron and light microscopes.

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There are 2 types of electron microscope, the scanning electron microscope and transmission electron microscope.  Transmission electron microscope create a 2D image of the cross-section of a sample, this microscope type has the highest resolving power.  Scanning electron microscopes give a 3D effect and show surface detail.

When looking at a specimen under an electron microscope the specimen must thin enough for electrons to pass through, about as thin as the film around a soap bubble.  There are two ways of preparing a sample for electron microscopy, negative staining and freezing.  Negative staining involves using an element such as uranium or gold to stain a sample.  An electron micrograph is an electron density map.  Elements such as Carbon, Hydrogen and Oxygen, which make up the largest portion of most cells, are not electron dense (do not contain many electrons), so they create a faint electron micrograph.  Staining the sample with elements which are electron dense means that there is a large contrast and the sample can be seen more clearly.

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I think these differences mean there is a demand for both microscopes, although the electron microscope has revolutionised cell biology there will always be a need for the light microscope.

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