section 1: cell structure - topic 4: how microscopes work Flashcards
what is magnification?
how much bigger the image is than the specimen.
what is the equation for magnification?
magnification = image size / object size
what is resolution?
resolution is how detailed the image is - the minimum distance between 2 objects where they can be differentiated as separate.
what are the 4 types of microscopes?
light.
laser scanning confocal.
transmission electron.
scanning electron.
what do light microscopes use?
light.
what is the resolution of light microscopes?
they have a lower resolution of electron microscopes.
they have a maximum resolution of about 0.2 micrometers.
what are light microscopes used to look at?
whole cells or tissues.
what are laser scanning confocal microscopes?
they are a special type of light microscope that use laser beams to scan a specimen that’s usually tagged with fluorescent dyes.
what is the maximum useful magnification of a light microscope?
about x1500.
how do laser scanning confocal microscopes work?
a laser beam is focused through a lens which is aimed at a beam splitter.
this splits the beam and some of the light is directed to the specimen.
when the laser hits the dyes, it causes them to give off fluorescent light.
this light is then focused through a pinhole onto a detector.
the detector is hooked up to a computer, which generates an image.
the pinhole means that any out-of-focus light is blocked, so these microscopes produce a much clearer image than a normal light microscope.
what are laser scanning confocal microscopes used to look at?
they can be used to look at objects at different depths in thick specimens.
what kind of pictures do laser scanning confocal microscopes produce?
multiple images produced by the microscope can be combined by the computer to generate 3D images of a specimen.
what do electron microscopes use?
electrons.
what is the resolution of electron microscopes?
they have a higher resolution than light microscopes, so give more detailed images.
what are the 2 types of electron microscopes?
TEM.
SEM.
how do TEMs work?
they use electromagnets to focus a beam of electrons, which is then transmitted through the specimen to produce 2D images.
denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
why are TEMs good?
because they provide high resolution images, so can be used to look at very small organelles i.e. ribosomes.
can also be used to look at the internal structures of organelles in detail.
limitations of TEMs?
specimens viewed on TEMs need to be quite thinly sliced.
the angle at which specimens are cut can affect how they appear.
how do SEMs work?
they scan a beam of electrons across the specimen.
this knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.
strengths of SEMs?
the images produced show the surface of the specimen & can be 3D.
limitations of SEMs?
they give lower resolution images than TEMs.
how do you prepare samples for electron microscopes?
they are treated with a solution of heavy metals (like lead).
the metal ions act to scatter the electrons that are fired at the sample and give contrast between different structures.
what do images produced by electron microscopy look like?
they are always black & white, although colour can be added to images after they’ve been made to make them easier to interpret.
summary of max. resolution & max. magnification.
light: 0.2 micrometres
x1500
TEM: 0.0002 micrometres
can be more than x1,000,000
SEM: 0.002 micrometres
usually less than x500,000
