microscopy Flashcards
what is the magnification equation?
magnification = size of image / size of real object
what is the resolution/ resolving power of a microscope?
the minimum distance apart that two objects can be in order for them to appear as separate items
what is the resolution of an optical microscope determined by?
the wavelength of light
what is the resolution of an electron microscope determined by?
the wavelength of the beam of electrons
what is magnification?
how many times larger the image is compared to the object
how do optical microscopes work?
beam of light focused with lenses
the wavelength of the beam is extremely long
how is the resolution of optical microscopes?
low (2 micrometers) so we can only see larger organelles and we can’t see detailed structure within organelles
what does the specimen need to have for optical microscopes?
needs to be thin enough for light to pass through
needs staining because lots of biological molecules are colourless
can we view living specimens in an optical microscope?
Yes
what kind of image is produced with an optical microscopes?
flat and 2D- coloured image
how do electron microscopes work?
uses a beam of electrons to produce an image. The beam is focused with electromagnets
how long is the wavelength of the beam of electrons in electron microscopes?
short which means a high resolving power
compare the resolution of transmission electron microscope and scanning electron microscope?
TEM- highest resolving power (0.1nm)
SEM- greater than optical microscope (20nm)
in a TEM, what does the specimen need to be?
-needs to be extremely thin so that electrons can pass through
-needs to be placed in a vacuum (so cannot be living)
-staining is complicated
what does an image look like on a TEM?
flat and 2D
black and white
parts of the specimen which are denser absorb more electrons and appear darker
how might colour be seen in a TEM?
due to staining or natural pigments in the specimen- generally the image does not have colour
what bad things can images produced by electron microscopes?
artefacts (things that aren’t part of the specimen but are result of specimen preparation)- so we can’t be sure that what is seen exists in that form
in a SEM, how does the specimen need to be?
-doesn’t need to be very thin because electrons don’t penetrate
-staining is complicated
-specimen must be placed in a vacuum (so no living specimens)
how is an image produced in an SEM?
beam of electrons is directed from above (instead of penetrating from below) and it is passed backwards and forwards across the specimen in a regular pattern
electrons are scattered by the specimen and the pattern of scattering depends on contours of the specimen surface
what kind of image is produced by a SEM?
a 3D image is produced by computer analysis of the pattern of scattered electrons
black and white-any colour added was using the computer
