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A Level Biology > Methods to Study Cells > Flashcards

Methods to Study Cells Flashcards

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1
Q

which methods help to determine the internal structure of cells

A

-microscopes
-cell fractionation
-ultracentrifugation

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2
Q

what are the three key types of microscopes

A

-optical microscopes
-transmission electron microscopes
-scanning electron microscopes

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3
Q

define magnification

A

how many times larger the image is compared to the object

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4
Q

define resolution

A

the minimum distance between two objects in which they can still be viewed as separate
the resolution in an optical microscope is determined by the wavelength of light
and the wavelength of the beam of electrons determines the resolution of an electron microscope

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5
Q

features of an optical (light) microscope

A
  • a beam of light is condensed to create the
    image
  • a glass lens is used to condense the beam of
    light
  • poorer resolution due to light having a longer wavelength
  • lower magnification
  • coloured images
  • can view living samples
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6
Q

features of an electron microsope (scanning or transmission)

A
  • a beam of electrons is condensed to create the
    image
  • electromagnets are used to condense the
    beam
  • higher resolving power as electrons have a shorter wavelength
  • higher magnification
  • black and white images
  • the sample must be in a vacuum, and therefore non-living
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7
Q

why do light microscopes have a poor resolution

A

the long wavelength of light

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8
Q

what can you observe with an optical microscope

A
  • small organelles in a cell are not visible
  • living samples can be examined and a coloured image is obtained
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9
Q

why must samples be in a vacuum for electron microscopes

A
  • electrons are absorbed by air
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10
Q

what can you examine with an electron microscope

A

-only non living specimens
-the image remains in black and white although samples are stained

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11
Q

how do transmission electron microscopes work

A

-extremely thin specimens are stained and placed in a
vacuum
-an electron gun produces a beam of electrons that passes through the specimen
-some parts absorb the electrons and appear dark

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12
Q

describe the image from a TEM

A

the image produced is 2D and shows detailed images of the internal structure of cells

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13
Q

how do scanning electron microscopes work

A

-the specimens do not need to be thin, as the electrons are
not transmitted through
-instead, the electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours

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14
Q

describe the image from an SEM

A

a 3D image is produced

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15
Q

formula for size of structures viewed under an optical microscope

A

image size = actual size x magnification

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16
Q

formula for magnification of an image

A

magnification = image size/ actual size

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17
Q

order for units

A

metre
millimetre
micrometre
nanometre

18
Q

order for conversion (largest to smallest)

A

x1000
x1000
x1000

19
Q

order for conversion (smallest to largest)

A

divide by 1000
divide by 1000
divide by 1000

20
Q

what is the eyepiece graticule

A

a scale on a glass disc

21
Q

what is the use of the eyepiece graticule

A

measure the size of objects you are viewing under the microscope

22
Q

what do you have to do each time you change the objective lens and therefore the magnification

A

calibrate the eyepiece to work out what the distance is between each division at that magnification

23
Q

what is used to calibrate the eyepiece graticule

A

a stage micrometer

24
Q

what is a stage micrometer

A

a glass slide with a scale on it which you place on the stage

25
Q

what is the scale on a stage micrometer

A

typically 2mm long and the sub-divisions are 10µm apart

26
Q

steps for calibrating the eyepiece graticule

A

step 1 - line up the stage micrometer and
eyepiece graticule whilst looking through the
eyepiece
step 2 – count how many divisions on the
eyepiece graticule fit into one division on the
micrometer scale
step 3 – each division on the micrometer is 10µm,
so this can be used to calculate what one division
on the eyepiece graticule is at that current
magnification

27
Q

what can you do once the graticule is calibrated

A

measure the size of cells or organelles

28
Q

what are cell fractionation and ultracentrifugation used for

A

used to break down cells and remove organelles so that they can be studied

29
Q

what happens during cell fractionation

A

-cells are broken down so that the organelles are free to be
separated
-this is done using a homogeniser (blender)

30
Q

conditions needed during homogenisation

A

-cold
-isotonic
-buffered

31
Q

why must the cells be kept in a cold solution during homogenisation

A

to reduce enzyme activity to prevent the breakdown of cell
components

32
Q

why must the cells be kept in an isotonic solution during homogenisation

A

to prevent any movement of water by osmosis which could result in organelles shrivelling or bursting

33
Q

why must the cells be kept in a buffered solution during homogenisation

A

-to resist pH changes
-this is to prevent damage to organelles and enzymes

34
Q

what is done once the cell has been broken open in cell fractionation

A

the solution must be filtered to remove larger pieces of debris

35
Q

what happens once the homogenate solution is filtered

A

it is ready to be centrifuged

36
Q

what happens when the solution is centrifuged

A

the solution is placed into a centrifuge which spins at high speed to separate organelles depending on their density due to the centrifugal force

37
Q

what does the supernatant contain after the first spin at low speed

A

pellet containing the nuclei

38
Q

what does the supernatant contain after the second spin at medium speed

A

pellet contains mitochondria and chloroplasts (if a plant
cell)

39
Q

what does the supernatant contain after the third spin at high speed

A

pellet contains lysosomes and SER/RER

40
Q

what does the supernatant contain after the fourth spin at very high speed

A

pellet contains ribosomes

A Level Biology (18 decks)

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