what does a transmission electron microscope do?
This, for example: http://upload.wikimedia.org/wikipedia/commons/d/de/Chlamydomonas_TEM_17.jpg Those are cross-sections through flagella, incidentally.
The transmission electron microscope (TEM) operates on the same basic principles as the light microscope but uses electrons instead of light. What you can see with a light microscope is limited by the wavelength of light. TEMs use electrons as "light source" and their much lower wavelength makes it possible to get a resolution a thousand times better than with a light microscope.
As you can see, everyone who has answered you so far has given you an answer that sounds way to complicated. So I am going to break it down for you. A transmissionelectron microscope passes a beam of electrons through a thin specimen (the object you are looking at) simular to how a compound light microscope transmitts light. (it shines electron light through the object to make it more visible.)
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