2.3 More microscopy

Question 1

how does a TEM work

Answer 1

beam of electrons transmitted through a specimen and then focused to produce an image

Question 2

how does a SEM work

Answer 2

beam of electrons sent across the surface of a specimen and the reflected electrons are collected

Question 3

sample preparation for electron microscopes

Answer 3

1. fixation using chemicals / freezing
2. staining with heavy metals
3. dehydration with solvents

TEM= set in resin and stained again
SEM= fractured to expose insides and coated with heavy metals

Question 4

magnification and resolution of light microscope

Answer 4

magnification = x2000

resolution = 200nm

Question 5

magnification and resolution of TEM

Answer 5

magnification = x500,000

resolution = 0.5nm

Question 6

magnification and resolution of SEM

Answer 6

magnification = x500,000

resolution = 3-10nm

Question 7

advantages of light microscopes (6)

Answer 7

\+ inexpensive to buy/operate
\+ small/portable
\+ simple sample preparation 
\+ no vacuum required
\+ natural colour
\+ dead or living specimens

Question 8

disadvantages of light microscopes (2)

Answer 8

• low resolution

- low magnification

Question 9

advantages of electron microscopes (4)

Answer 9

+ high resolution
+ high magnification
+ SEM produces 3D images
+ images can be coloured digitally

Question 10

disadvantages of electron microscopes (5)

Answer 10

• expensive to buy/operate
• large
• complex sample preparation
• sample preparation = distortion
• specimens must be dead

Question 11

what is an artefact

Answer 11

• visible structural detail caused by processing of a specimen
• seen as the loss of continuity in membranes, distortion of organelles and empty spaces in the cytoplasm

Question 12

define fluorescence

Answer 12

absorption and re-radiation of light

Question 13

why are LSCMs used

Answer 13

to look at objects at different depths in thick specimens

Question 14

how do LSCMs work

Answer 14

1. single spot of focused light moves across specimen
2. causes fluorescence from components labelled with a ‘dye’
3. emitted light is filtered through pinhole aperture (only close to focal plane is detected)

Question 15

advantages of LSCMs (3)

Answer 15

+ 2D and 3D images
+ non-invasive
+ high resolution images

Question 16

disadvantages of LSCMs (2)

Answer 16

• samples have to be thin

- unwanted radiation would cause blurring and reduce resolution