1.5 Electron microscopy Flashcards
Define resolution
The ability to distinguish between two separate points
If two points cannot be resolved
then they will be seen as one point
The images with a higher resolution are more
clear and detailed
The maximum resoution of a light microscope is
200 nm
A resolution of 200nm means
that if two points are closer than 200nm then they cant be distinguished as separate
One of the properties of light is that
It travels in waves
The lengths of the waves of visible light vary from
400nm to 700nm
How can the human eye see the light waves as colors
The human eye can distinguish between these differences and in the brain, the differences are converted into color differences.
What is the electromagnetic spectrum?
The range of different wavelengths of electromagnetic radiation
Visible light is a form of
electromagnetic radiation
Waves that are 400 nm are seen as
Violet
Waves that 700 nm in length are seen as
red
The greater the energy of the wave
the shorter the wavelength
The longer the waves
Thelower their frequency
Why can a mitochondrion be seen using a light microscope but not s ribosome
The mitochondrion is large enough to interfere with the light waves. However, the ribosome are far too small to have any effect on the light waves.
The general rule when viewing specimens is that the limit of resolution
is about one half of the wavelength the wavelength of the radiation used to view the specimen.
If an object is smaller than half the wavelength of the radiation used to view the specimen
then it cannot be seen separately from nearby objects
Why can a transparent object not be seen using light microscope
It will allow light waves to pass through itself and therefore still not be visible
Why are electrons a suitable form of radiation to look at things smaller than 200nm
They have extremely short wavelengths
They are negatively charged so they can be focused easily using electromagnets
Why do electrons have such short frequency
because they have great amounts of energy (especially after being heated)
When do the electrons behave like an electromagnetic radiation?
When a metal becomes very hot, some of its electrons gain so much energy and escape from their orbits. Free electrons behave like electromagnetic radiation.
Explain the importance of electromagnets in an electron microscope
A magnet can be used to alter the path of the beam, equivalent of a glass lens bending light.
What is the resolution obtained using electron microscope?
0.5 nm
What are the two types of electron microscope in use?
Transmission electron microscope(TEM)
Scanning electron microscope(SEM)
What type of electron microscope was the one originally developed?
Transmission electron microscope
How does TEM work
The beam of electrons is passed through the specimen before being viewed. Only the electrons that are transmitted (pass through the specimen) are seen. This allows us to see thin sections of the cells and thus see inside them.
How does SEM work?
The electron beam is used to scan the surfaces of structure. They hit the structure and only the reflected veam is observed.
What is an advantage of SEM
The surface structures can be seen
What is a disadvantage of SEM
It cannot give the same resolution as TEM. Using a SEM, a resolution between 3nm and 20nm is obtained.
It is not possible to see an electron beam. How is this problem solved?
The electron beam has to be projected into fluorescent screen. The areas hit by electrons shine brightly giving an overall black and white image.
The stains used to improve the contrast of biological molecules in electron microscopy contain
heavy metal atoms, which stop the passage of electrons.
What are false-color images?
These are images that form when the standard black and white images formed using an electron microscope by using a computer.
Why should the electron beam as well as the specimen and the fluorescent screen be in a vacuum?
If the electrons collided with air molecules, they would scatter making it impossible to achieve a sharp picture.
Why must all specimens be dehydrated before being placed in the microscope
Water boils at room temperature in a vacuum.
Why can only dead materials be examined using electron microscope?
It is because all specimens must be dehydrated before being placed in the electron microscope. However, great efforts are made to try to preserve material in a life like state.
