AQA Biology 3.2 The electron microscope

Question	Answer
what are the two main advantages of an electron microscope?	-short wavelength so has high resolving power -electrons are negatively charged so beam con be focused using electromagnets
what is bad about electron microscopes?	electrons are absorbed by molecules in air so a near-vacuum must be created in the chamber of the microscope
what are the two types of electron microscope?	-Transmission electron microscope (TEM) -Scanning electron microscope (SEM)
How does a TEM work?	beam fired at sample, some passes through parts of the specimen so appears light but some parts absorb electrons so appears dark.
how is the image shown?	on a screen
what can this be photographed to produce?	a photomicrograph
what are 4 limitations of the TEM?	-needs a vacuum -complex staining process required and then is only black and white image -specimen must be extremely thin - may contain artefacts
how does an SEM work?	electron beam passed back and forth in a regular pattern. Electrons are scattered by specimen and pattern of this scattering depends on contours of specimen surface. Image built up on computer
what is the resolving power of an SEM compared to a TEM and a light microscope?	SEM = 20nm TEM = 0.1nm light = 0.2 um

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	Created by Charlotte Hewson over 9 years ago