Cells Microscopy- Electron Microscope Flashcards
Why do light microscopes have a poor resolution?
Relatively long wavelength of light.
What are the two main advantages of an electron microscope?
The electron beam has a very short wavelength and the microscope can therefore resolve objects well - it has a high resolving power.
As electrons are negatively charged the beam can be focused using electromagnets.
What’s the electron microscope resolution?
Can resolve objects that are just 0.1 nm apart - 2000 times better than a light microscope.
How does the electron microscope work?
Electrons are absorbed or deflected by the molecules in the air, a near-vacuum has to be created within the chamber of an electron microscope in order for it to work effectively.
What are the components making up a light microscope?
Light source.
Condenser lens.
Object.
Objective lenses.
Intermediate image.
Eyepiece lenses.
What are the components making up an electron microscope?
Electron source.
Magnetic condenser.
Object.
Magnetic objective.
Intermediate image.
Magnetic projector.
Fluorescent screen.
What are the two types of electron microscope?
The scanning electron microscope (SEM).
The transmission electron microscope(TEM).
The TEM: how does it work?
The TEM consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet. In a TEM, the beam passes through a thin section of the specimen. Parts of this specimen absorb electrons and therefore appear dark because they’re more dense. Other parts of the specimen allow the electrons to pass through and so appear bright.
In a TEM why can a 0.1 resolving power not always be achieved?
Difficulties preparing the specimen limit the resolution that can be achieved.
A higher energy electron beam is required and this may destroy the specimen.
What are the limitations of the TEM?
The whole system mist be in a vacuum and therefore living specimens cannot be observed.
A complex ‘staining’ process is required and even then the image is not in colour.
The specimen must be extremely thin.
Artefacts could come up on the photomicrograph from when they were being prepared.
What is a result of the specimen having to be thin in a TEM?
This is to allow electrons to penetrate. The result is therefore a flat 2-D image.
What are the limitations of the scanning electron microscope?
All the limitations of the TEM also apply to the SEM except from the specimen does not have to be extremely thin as electrons don’t penetrate it.
SEM microscope: how does it work?
The SEM directs a beam of electrons on to the surface of the specimen for above, rather than penetrating it from below. The beam is then passed back and forth across a portion of the specimen and the pattern of this scattering depends on the contours of the specimen surface. We build up a 3-D image by computer analysis of the pattern of this scattered electrons and secondary electrons produced.
What is the resolving power of a scanning electron microscope?
20 nm 10 x better than a light microscope.
