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All living organisms (except viruses which do not show all of the characteristics of living
things) are made up of one or more cells. A cell is always surrounded by a cell surface
membrane, and contains a solution of proteins and other substances in water. This solution
is called…

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Microscopes are instruments that magnify the image of an object.

A simple convex glass lens can act as a magnifying glass but such lenses work more
effectively if they are in a compound light microscope.

The relatively long wavelength of the light rays mean that a light microscope can…

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Light Microscopes
The simplest form of microscope is single lens, but it has very limited powers of
magnification ­ around x1500

In the compound microscope, as shown below, two lenses are used.

They have a resolution of about 0.2µm

Light rays are focused on to a transparent specimen by a…

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Electron Microscopes
The limitations of the light microscope led scientists to consider the use of forms of
radiation with shorter wavelengths.

This led to the development of the first electron microscope.

This instrument works on the same principal of the light microscope except that instead of
light rays, a beam…

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The Transmission Electron Microscope
It consists of an electron gun that produces a beam of electrons that is focused onto
the specimen by a condenser electromagnet.

The beam passes through a thin section of the specimen. Parts of this specimen absorb
electrons and therefore appear dark.

Other parts of the…

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Scanning Electron Microscope
All the limitations of the TEM also apply to the scanning electron microscope, except that
specimens need not be extremely thin as electrons do not penetrate.

The SEM directs a beam of electrons on to the surface of the specimen in a regular

The electrons are…

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Comparisons of advantages and disadvantages of
the light and electron microscope

Light Microscope Electron Microscope

Cheap to purchase (£100 ­ 500) Expensive to buy (over £ 1 000 000).

Cheap to operate. Expensive to produce electron beam.

Small and portable. Large and requires special rooms.

Simple and easy sample preparation.…




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