microscopes Flashcards
magnification
how many times bigger the image produced by the microscope is than the real-life object you are viewing
resolution
the ability to distinguish between objects/points that are close together
what do optical microscopes use?
they use light to form an imagr
resolution of optical microscopes
-using light, can’t distinguish between two objects that are closer than half the wavelength of light → low resolution
-maximum resolution of around 0.2
micrometres
what can optical microscopes be used to observe?
-eukaryotic cells, their nuclei (possibly mitochondria and chloroplasts)
-living specimens
maximum magnification of optical microscopes:
1500x
what do electron microscopes use?
they use electrons to form an image
resolution of electron microscopes
-high resolution
-a beam of electrons has a much smaller wavelength than light
-maximum resolution of 0.0002 pm
what can electron microscopes be used to observe?
small organelles
what is the maximum magnification of electron microscopes?
×1,500,000
what are the two types of electron microscopes?
trasmission electron microscopes:
(TEMs)
scanning electron microscopes:
(SEMs)
how do TEMS work?
-use electromagnets to focus a beam of electrons
-beam of electrons is transmitted through the specimen
-denser parts of the specimen absorb more electrons & appear darker on the final image produced
advantages of TEMs
-give high-resolution images
-allows small organelles to be seen
disadvantages of TEMs
-can only be used with very thin specimens
-cannot be used to observe live specimens (as there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed)
-the lengthy treatment required to prepare specimens means that artefacts can be produced (artefacts look like real structures but are actually the results of preserving and staining)
-do not produce a colour image
how do SEMS work?
-scan a beam of electrons across the specimen
-beam bounces off the surface of the specimen and the electrons are detected, forming an image
-this means SEMs can produce 3D images that show the surface of specimens
advantages of SEMs:
-can be used on thick or 3-D specimens
-allow the 3-D structure of specimens to be observed
disadvantages of SEMs:
-lower resolution images than TEMs
-cannot be used to observe live specimens
-no colour image
electron microscope vs light microscope (basic differences)
large and can’t be moved (e) v small and easy to carry (l)
-vacuum needed (e) v no vacuum needed (l)
-complicated sample preparation (e) v simple sample preparation (I)
-over 500,000x magnification (e) v up to 2,000x magnification (l)
-specimens are dead (e) v specimens can be living (l)
the start of using an optical microscope:
start with the low power objective lens
→ it’s easier to find what you’re looking for in the field of view
→ this helps to prevent damage to the lens or coverslip, incase the stage has been raised too high
where & how can graticules be used?
they can be placed into the eyepiece of a microscope to act as a ruler in the field of view
what must be done with a graticule?
it must be calibrated for the objective lens that is in use
how is calibration done?
this is done by using a stage micrometer
-by using the two scales together, you can find out how many micrometers each graticule unit is worth
rules of biological drawings:
-the drawing must have a title
-the magnification under which the observations were made must be recorded
-no shading
-label lines should be kept to one side of the drawing
how many different lenses does a light microscope have?
two:
-an eyepiece lens
-an objective lens
