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AQA A Level Biology > Methods of Studying Cells > Flashcards

Methods of Studying Cells Flashcards

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1
Q

what is an object?

A

material put under a microscope

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2
Q

what is an image?

A

the appearance of the object when viewed under a microscope

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3
Q

magnification =

A

size of image divided by size of object

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4
Q

resolution definition

A

the minimum distance apart that two objects can be for them to appear as separate items under a microscope

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5
Q

what does the resolving power of a microscope depend on?

A

the wavelength or form of radiation used

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6
Q

what does a greater resolution produce?

A

a clearer and more precise image

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7
Q

does increasing magnification always increase the resolution?

A

no - there is a limit

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8
Q

what happens if you increase the magnification past the limit of the resolution?

A

the image will get larger but more blurry

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9
Q

what is homogenisation?

A

breaking up cells in a blender (homogeniser) to release the organelles

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10
Q

what is another name for the resultant fluid of homogenisation?

A

homogenate

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11
Q

what happens to the homogenate?

A

it is filtered to remove complete cells and unwanted debris

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12
Q

ultracentrifugation definition

A

the process by which fragments in a filtered homogenate are separated in a centrifuge

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13
Q

what is the importance of cell fractionation?

A

obtaining large numbers of isolated organelles allows scientists to study their structure and function

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14
Q

cell fractionation step 1

A

place tissue in a cold, buffered, isotonic solution

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15
Q

why is the solution cold?

A

to reduce enzyme activity that might break down the organelles

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16
Q

what is isotonic?

A

same water potential

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17
Q

why is the solution isotonic?

A

to prevent organelles bursting/shrinking due to osmotic gain/loss of water

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18
Q

why is the solution buffered?

A

to maintain pH to retain the integrity of the organelles

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19
Q

cell fractionation step 2

A

homogenise the solution

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20
Q

cell fractionation step 3 (and the first step of ultracentrifugation)

A

spin the homogenised tissue in a centrifuge at a low speed (1000 X gravity) for 10 minutes. Filter the homogenate to remove unwanted debris.

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21
Q

what does a centrifuge create?

A

a centrifugal force

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22
Q

cell fractionation step 4 (and the second step of ultracentrifugation)

A

spin the supernatant (left over) at a medium speed (3500 X gravity). Filter the homogenate to remove unwanted debris.

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23
Q

cell fractionation step 5 (and the third step of ultracentrifugation)

A

spin the new supernatant at a high speed (16500 X gravity)

24
Q

what is removed at each increase in speed during ultracentrifugation?

A

the next heaviest organelles

25
Q

what is the heaviest organelle?

A

nucleus

26
Q

what is the lightest organelle?

A

ribosomes

27
Q

what is the second heaviest organelle?

A

chloroplasts

28
Q

what is the second lightest organelle?

A

ER

29
Q

what is the third heaviest organelle?

A

mitochondria

30
Q

what is the third lightest organelle?

A

lysosomes

31
Q

how does an optical microscope work?

A

light is sent from a light source through a specimen, the image of which is magnified by glass lenses

32
Q

what was the first type of microscope invented?

A

the light microscope

33
Q

what is the most common type of microscope?

A

the light microscope

34
Q

why are light microscopes the most common?

A

cheap, easy to use, can study living cells

35
Q

what type of image does a light microscope produce?

A

2D

36
Q

what is the resolution of a light microscope limited to?

A

200nm or 0.2 micrometers

37
Q

why is the resolution of a light microscope limited?

A

light has a relatively long wavelength

38
Q

what is the magnification of a light microscope limited to?

A

X 2000

39
Q

why are stains needed for objects under light microscopes?

A

individual cells are generally transparent and their components are not distinguishable unless they are coloured with special stains

40
Q

what is a problem with using stains?

A

it usually kills the cells

41
Q

what organelles can you see with a light microscope?

A

nucleus and mitochondria

42
Q

what do electron microscopes use instead of light?

A

a beam of electrons

43
Q

why do electron microscopes have a higher resolving power?

A

the electron beam has a shorter wavelength than light

44
Q

how is the image of an electron microscope produced?

A

specimens are not directly observed. A computer forms an image based on how many electrons are absorbed by different regions of the specimen

45
Q

what is the resolution of some of the best electron microscopes?

A

0.1 nm (2000X more than light)

46
Q

what are scanning electron microscope images created from?

A

the electrons that are reflected off the specimen

47
Q

how do both SEM and TEM work?

A

directs a beam of electrons at a specimen

48
Q

how is the beam of electrons focused?

A

electromagnets

49
Q

what are the images produced by SEM like?

A

3D and detailed

50
Q

do specimens have to be thin when using a SEM?

A

no

51
Q

Which has a slightly lower resolution: SEM or TEM?

A

SEM (1nm)

52
Q

why are SEM and TEM images black and white?

A

electrons don’t correspond to light and colour.

Colour can be added artificially to these images

53
Q

what are some cons to using a SEM or TEM?

A

expensive

need training to operate it

54
Q

why must samples be dead for a SEM or TEM?

A

electrons can be deflected by molecules in the air so a vacuum is needed

55
Q

how are images from TEM created?

A

from the electrons that are absorbed by the specimen

56
Q

how is the magnification of TEM compared to SEM?

A

2X magnification of SEM

57
Q

what is the main con of a TEM?

A

sample must be thin

AQA A Level Biology (5 decks)

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