2.1.3 Methods of studying cells

Question 1

Describe the difference between magnification and resolution

Answer 1

● Magnification =number of times greater image is than size of the real (actual) object
○ Magnification = size of image / size of real object

● Resolution = minimum distance apart 2 objects can be to be distinguished as separate objects

Question 2

In an optical microscope what is the light focused using?

Answer 2

a glass lens

Question 3

In an transmission electron microscope (TEM) what are electrons focused using?

Answer 3

Electrons focused using electromagnets

Question 4

In a scanning electron microscope (SEM) what are electrons focused using?

Answer 4

Electrons focused using electromagnets

Question 5

What does the light do through a specimen in an optical microscope?

Answer 5

Light passes through specimen, different structures absorb different amounts & wavelengths

Question 6

What does the electrons do through a specimen in an TEM?

Answer 6

Electrons pass through specimen, denser parts absorb more and appear darker

Question 7

What do the electrons do through a specimen in a SEM?

Answer 7

Electrons deflected / bounce off specimen surface

Question 8

What type of image does an optical microscope produce?

Answer 8

Generates a 2D image of a cross-section

Question 9

What type of image does a TEM produce?

Answer 9

Generates a 2D image of a cross-section

Question 10

What type of image does a SEM produce?

Answer 10

Generates a 3D image of surface

Question 11

What type of resolution does an optical microscope have?

Answer 11

Low resolution due to long wavelength of light

Question 12

What type of resolution does a TEM have?

Answer 12

Very high resolution due to short wavelength of electrons

Question 13

What type of resolution does a SEM have?

Answer 13

High resolution due to short wavelength of electrons

Question 14

Can you see internal structures using an optical microscope?

Answer 14

Can’t see internal structure of organelles or ribosomes

Question 15

Can you see internal structures using a TEM?

Answer 15

Can see internal structures of organelles and ribosomes

Question 16

Can you see internal structures using a SEM?

Answer 16

Can’t see internal structures

Question 17

What does the specimen have to be in an optical microscope?

Answer 17

Specimen = thin

Question 18

What does the specimen have to be in a TEM?

Answer 18

Specimen = very thin

Question 19

What does the specimen have to be in a SEM?

Answer 19

Specimen does not need to be thin

Question 20

What is the magnification like on an optical microscope?

Answer 20

Low magnification (x 1500)

Question 21

What is the magnification like on a TEM?

Answer 21

High magnification (x 1,000,000)

Question 22

What is the magnification like on a SEM?

Answer 22

High magnification (x 1,000,000)

Question 23

Can you view living organisms on an optical microscope?

Answer 23

Can view living organisms

Question 24

Can you view living organisms on a TEM?

Answer 24

Can only view dead/dehydrated specimens as uses a vacuum

Question 25

Can you view living organisms on a SEM?

Answer 25

Can only view dead/dehydrated specimens as uses a vacuum

Question 26

Can optical microscopes show colour?

Answer 26

Yes

Question 27

Can a TEM show colour?

Answer 27

No

Question 28

Can a SEM show colour?

Answer 28

No

Question 29

Suggest how the scientific community distinguished between artefacts (eg. dust, air bubbles occurring during preparation) and cell organelles

Answer 29

● Scientists prepared specimens in different ways ● If an object was seen with one technique but not another, it was more likely to be an artefact than an organelle

Question 30

List the steps in calculations involving magnification, real size &image size

Answer 30

1. Note formula / rearrange if necessary (I = AM) 2. Convert units if necessary- image and actual size must be in same unit 3. Calculate answer and check units required or if standard form etc. is required

Question 31

How many meters is cm equivalent to?

Answer 31

1/100m 0.01m 10^-2m

Question 32

How many meters is a mm equal to?

Answer 32

1/1000m 0.001m 10^-3m

Question 33

How many meters is a um equal to?

Answer 33

1/1,000,000 0.000001m 10^-6m

Question 34

How many meters is a nm equal to?

Answer 34

10^-9m

Question 35

Describe how the size of an object viewed with an optical microscope can be measured

Answer 35

1 . Line up (scale of) eyepiece graticule with (scale of) stage micrometre 2. Calibrate eyepiece graticule- use stage micrometre to calculate size of divisions on eyepiece graticule 3. Take micrometre away and use graticule to measure how many divisions make up the object 4. Calculate size of object by multiplying number of divisions by size of division 5. Recalibrate eyepiece graticule at different magnifications

Question 36

What is the first step of cell fractionation?

Answer 36

1. Homogenise tissue/ use a blender

Question 37

Why do we homogenise tissue/ use a blender?

Answer 37

Disrupts the cell membrane, breaking open cells to release contents/organelles

Question 38

What is the second step in cell fractionation?

Answer 38

2. Place in a cold, isotonic ,buffered solution

Question 39

Why do we place in a cold, isotonic, buffered solution?

Answer 39

● Cold to reduce enzyme activity ○ So organelles not broken down/damaged ●Isotonic so water doesn’t move in or out of organelles by osmosis ○ So they don’t burst ● Buffered to keep pH constant ○ So enzymes don’t denature

Question 40

What is the third step of cell fractionation?

Answer 40

3. Filter homogenate

Question 41

Why do we filter homogenate?

Answer 41

● Remove large, unwanted debris eg. whole cells, connective tissue

Question 42

What is ultra centrifugation?

Answer 42

separates organelles in order of density/ mass

Question 43

What is the process of ultra centrifugation?

Answer 43

● Centrifuge homogenate in a tube at a low speed ● Remove pellet of heaviest organelle and re-spin supernatant at a higher speed ● Repeat at increasing speeds until separated out, each time the pellet is made of lighter organelles (nuclei→chloroplasts/mitochondria→lysosomes→ER→ribosomes)