microscopy

Question 1

what is the magnification equation?

Answer 1

magnification = size of image / size of real object

Question 2

what is the resolution/ resolving power of a microscope?

Answer 2

the minimum distance apart that two objects can be in order for them to appear as separate items

Question 3

what is the resolution of an optical microscope determined by?

Answer 3

the wavelength of light

Question 4

what is the resolution of an electron microscope determined by?

Answer 4

the wavelength of the beam of electrons

Question 5

what is magnification?

Answer 5

how many times larger the image is compared to the object

Question 6

how do optical microscopes work?

Answer 6

beam of light focused with lenses
the wavelength of the beam is extremely long

Question 7

how is the resolution of optical microscopes?

Answer 7

low (2 micrometers) so we can only see larger organelles and we can’t see detailed structure within organelles

Question 8

what does the specimen need to have for optical microscopes?

Answer 8

needs to be thin enough for light to pass through
needs staining because lots of biological molecules are colourless

Question 9

can we view living specimens in an optical microscope?

Answer 9

Yes

Question 10

what kind of image is produced with an optical microscopes?

Answer 10

flat and 2D- coloured image

Question 11

how do electron microscopes work?

Answer 11

uses a beam of electrons to produce an image. The beam is focused with electromagnets

Question 12

how long is the wavelength of the beam of electrons in electron microscopes?

Answer 12

short which means a high resolving power

Question 13

compare the resolution of transmission electron microscope and scanning electron microscope?

Answer 13

TEM- highest resolving power (0.1nm)
SEM- greater than optical microscope (20nm)

Question 14

in a TEM, what does the specimen need to be?

Answer 14

-needs to be extremely thin so that electrons can pass through
-needs to be placed in a vacuum (so cannot be living)
-staining is complicated

Question 15

what does an image look like on a TEM?

Answer 15

flat and 2D
black and white

parts of the specimen which are denser absorb more electrons and appear darker

Question 16

how might colour be seen in a TEM?

Answer 16

due to staining or natural pigments in the specimen- generally the image does not have colour

Question 17

what bad things can images produced by electron microscopes?

Answer 17

artefacts (things that aren’t part of the specimen but are result of specimen preparation)- so we can’t be sure that what is seen exists in that form

Question 18

in a SEM, how does the specimen need to be?

Answer 18

-doesn’t need to be very thin because electrons don’t penetrate
-staining is complicated
-specimen must be placed in a vacuum (so no living specimens)

Question 19

how is an image produced in an SEM?

Answer 19

beam of electrons is directed from above (instead of penetrating from below) and it is passed backwards and forwards across the specimen in a regular pattern

electrons are scattered by the specimen and the pattern of scattering depends on contours of the specimen surface

Question 20

what kind of image is produced by a SEM?

Answer 20

a 3D image is produced by computer analysis of the pattern of scattered electrons

black and white-any colour added was using the computer