ELECTRON MICROSCOPES

Question 1

about electron microscopes

Answer 1

show a clearer and more detailed image than light microscopes
higher magnification
higher resolution

Question 2

why do electron microscopes have a higher resolution

Answer 2

electron beam has a shorter wavelength than light

Question 3

TEM

Answer 3

transmission electron microscope
beam of electrons passed through specimen
electrons pass through denser parts less easily so denser appears darker and so darker regions contain more structures
scattered electrons are captured on a photographic plate
2D
mag up to 250000x
res of 2nm

Question 4

SEM

Answer 4

scanning electron microscope
specimen coated in a thin layer of metal
electromagnet focuses a beam of electrons
electrons bounced off the surface onto a photographic plate
3D
mag 100000x
res of 3-20nm

Question 5

advantages of electron microscopes

Answer 5

higher resolution compared to light so smaller organelles can be seen
SEM produces 3D images

Question 6

limitations of electron microscopes

Answer 6

specimens must be in a vacuum so cannot see living specimens
images in black and white
complex staining process so image may contain artefacts
TEM specimens must be very thin to allow electrons to penitrate
TEM produces flat 2D images but can be overcome by taking a series of sections
SEM has a lower resolving power than TEM but still better than alight micriscope

Question 7

what are artefacts

Answer 7

images you can see down the microscope that arent part of the specimen
e.g. dust, air bubbles, fingerprints
usually during the preparation of the specimen