microscopes

Question 1

magnification

Answer 1

how many times bigger the image produced by the microscope is than the real-life object you are viewing

Question 2

resolution

Answer 2

the ability to distinguish between objects/points that are close together

Question 3

what do optical microscopes use?

Answer 3

they use light to form an imagr

Question 4

resolution of optical microscopes

Answer 4

-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

Question 5

what can optical microscopes be used to observe?

Answer 5

-eukaryotic cells, their nuclei (possibly mitochondria and chloroplasts)
-living specimens

Question 6

maximum magnification of optical microscopes:

Answer 6

1500x

Question 7

what do electron microscopes use?

Answer 7

they use electrons to form an image

Question 8

resolution of electron microscopes

Answer 8

-high resolution
-a beam of electrons has a much smaller wavelength than light
-maximum resolution of 0.0002 pm

Question 9

what can electron microscopes be used to observe?

Answer 9

small organelles

Question 10

what is the maximum magnification of electron microscopes?

Answer 10

×1,500,000

Question 11

what are the two types of electron microscopes?

Answer 11

trasmission electron microscopes:
(TEMs)
scanning electron microscopes:
(SEMs)

Question 12

how do TEMS work?

Answer 12

-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

Question 13

advantages of TEMs

Answer 13

-give high-resolution images
-allows small organelles to be seen

Question 14

disadvantages of TEMs

Answer 14

-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

Question 15

how do SEMS work?

Answer 15

-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

Question 16

advantages of SEMs:

Answer 16

-can be used on thick or 3-D specimens
-allow the 3-D structure of specimens to be observed

Question 17

disadvantages of SEMs:

Answer 17

-lower resolution images than TEMs
-cannot be used to observe live specimens
-no colour image

Question 18

electron microscope vs light microscope (basic differences)

Answer 18

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)

Question 19

the start of using an optical microscope:

Answer 19

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

Question 20

where & how can graticules be used?

Answer 20

they can be placed into the eyepiece of a microscope to act as a ruler in the field of view

Question 21

what must be done with a graticule?

Answer 21

it must be calibrated for the objective lens that is in use

Question 22

how is calibration done?

Answer 22

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

Question 23

rules of biological drawings:

Answer 23

-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

Question 24

how many different lenses does a light microscope have?

Answer 24

two:
-an eyepiece lens
-an objective lens

Question 25

objective lenses on a microscope:

Answer 25

a series of objective lenses, each with a different magnification

Question 26

magnification formula

Answer 26

I.A.M

image size/actual size = magnification

Question 27

mm → um

Answer 27

x1000

Question 28

um → nm

Answer 28

x1000

Question 29

the actual thickness of the leaf below is 2000um, but the image size of the leaf in the diagram is 50mm. what is the magnification of the diagram?

Answer 29

2000 / 1000 = 2, so the actual thickness of
the leaf is 2 mm and the image size is 50 mm

magnification = image size / actual size
50 / 2 = 25

magnification = x25