3.2 Electron microscopes

Question 1

two types of electron microscopes:

Answer 1

transmission electron microscope (TEM)
scanning electron microscope (SEM)

Question 2

TEM order of parts:

Answer 2

electron gun
specimen
lens
detector

Question 3

SEM order of parts:

Answer 3

electron gun
lens
specimen
detectors (above specimen)

Question 4

why does the sample have to be stained with heavy metal dyes?

Answer 4

the heavy metal dye is absorbed by the organelles
as electrons pass through, some are absorbed, and other pass through and hit the detectors
this is how the images are created

Question 5

images; TEM

Answer 5

flat 2D images with no colour

Question 6

specimens; TEM

Answer 6

specimens must be extremely thin in order for the electrons to be able to pass through

Question 7

resolution; TEM vs SEM

Answer 7

TEM has a higher resolution than TEM at 0.1 nm, and SEM at 20nm

Question 8

images; SEM

Answer 8

3D images with no colour

Question 9

how are images created in SEMs?

Answer 9

electrons are focused onto the specimen
electrons are scattered by its surface
detectors detect the electrons and create a 3D image of the specimen

Question 10

limitations of electron microscopes:

Answer 10

• specimen must be dead
• specimen must be viewed in a vacuum
• complex staining process, not even in colour
• specimen must be extremely thin
• images may contains artefacts

Question 11

what are artefacts?

Answer 11

distortions to the specimens caused by the harsh preliminary treatment (the way the specimen was prepared)