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biology > Cell structure - Microscopy > Flashcards

Cell structure - Microscopy Flashcards

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1
Q

how does a light microscope work

A

the light microscope focuses the light onto the specimen and then magnifies the image through a series of lenses

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2
Q

describe how to use the microscope

A

clip the slide onto the stage
turn on the light
select the lowest powered objective lens
use the coarse adjustment knob to move the objective lens to just above the slide
look down the eyepiece and adjust the focus by moving the lens away from the slide using the fine adjustment knob until a clear image appears

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3
Q

what are stains

A

coloured chemicals that bind to molecules in a specimen

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4
Q

what are the three uses of stains

A

makes cells visible
increases contrast (as different components of the cell take up different amounts of the stain)
detail inside cells can be seen eg organelles can be identified

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5
Q

2 examples of stains

A

methylene blue: stains living cells blue
iodine solution: stains starch grains blue black

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6
Q

describe the process of differential staining

A

using more than one chemical stain. different stains bind to specific structures. this can be used to show contrast between organelles, tissues and microorganisms

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7
Q

define magnification

A

the number of times larger an image is compared with the actual size of the object

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8
Q

what is the equation for magnification

A

M=I/A

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9
Q

define resolution

A

the ability to distinguish between two separate points that are very close together

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10
Q

why is a high resolution good

A

more detail can be seen with a higher resolution, resolution gives clarity

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11
Q

what is the max resolution of a light microscope

A

200nm

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12
Q

what is the max resolution of an electron microscope

A

0.2nm

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13
Q

how do electron microscopes create magnified images

A

by using electrons instead of light waves

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14
Q

why must samples be prepared carefully in an electron microscope

A

to withstand the vacuum inside the microscope

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15
Q

how do electron microscopes work

A

the air is pumped out the microscope and a beam of electrons is fired through a series of electromagnetic lenses which focus the electrons. the electrons are detected and turned into a black and white image (electron micrograph).

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16
Q

why is false colour sometimes added to electron microscope images

A

to make them easier to understand

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17
Q

how must the sample be prepared in a scanning electron microscope

A

sample must be dried carefully and coated thinly in gold

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18
Q

how is the sample prepared in a transmission electron microscope

A

sample must be sectioned thinly

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19
Q

how do SEM work

A

the beam moves back and forth across the specimen. electrons knocked off the specimen are detected

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20
Q

what is the resolution of SEM

A

2nm

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20
Q

what is the maximum magnification of SEM

A

x200,000

20
Q

describe the image produced by a TEM

A

2D, high resolution, internal structure

20
Q

how do TEM work

A

use electromagnets to transmit a beam of electrons through a specimen; denser parts of the specimen absorb more electrons, meaning that denser parts appear darker on the final image

20
Q

describe the image produced by a SEM

A

3D, surface of specimen

21
Q

what is the maximum magnification of TEM

A

x2,000,000

22
Q

what is the resolution of TEM

A

0.2nm

23
Q

what are SEM used to study

A

the surfaces of objects

24
Q

what are TEM used to study

A

the ultrastructure of cells

25
Q

compare the wavelengths of light and electron microscopes

A

light:400-700nm
electron:0.004nm

26
Q

compare the maximum magnifications of light and electron microscopes

A

light:x2000
SEM:200,000
TEM:2,000,000

27
Q

compare the resolution of light and electron microscopes

A

light:200nm
SEM:2nm
TEM:0.2nm

28
Q

compare how focusing is carried out by light and electron microscopes

A

light: by glass lenses
electron: electromagnetic lenses

29
Q

compare the costs to purchase and operate in light and electron microscopes

A

light: cheap
electron: expensive

30
Q

compare the sizes of light and electron microscopes

A

light: small
electron: large

31
Q

compare how materials are prepared in light and electron microscopes

A

light: easy
electron: hard

32
Q

in which microscope is a vacuum required

A

electron

33
Q

are the materials distorted by the preparation in light and electron microscopes

A

light: no/maybe
electron: yes

34
Q

are the specimens living or dead in light and electron microscopes

A

light: living or dead
electron: dead

35
Q

is colour observed in light and electron microscopes

A

light: yes
electron: no

36
Q

what is an eyepiece graticule

A

a printed scale in the microscope eyepiece

37
Q

how many units is an eyepiece graticule divided into

A

100 EPU

38
Q

what is a stage micrometer

A

a microscope slide which has a fine and accurate scale engraved on it

39
Q

how long is the micrometer scale usually used

A

1mm

40
Q

how many units is the micrometer scale usually divided into

A

100

41
Q

how long is each small division on a stage micrometer

A

10 micrometres

42
Q

does the calibration of the eyepiece graticule have to be done separately for each lens

A

yes

43
Q

describe simply how to calibrate an eyepiece graticule

A

line the scale on the stage micrometer with the scale on the eyepiece graticule and count the number of EPU that correspond to 1mm on the stage micrometer.

44
Q

what is the value of one EPU in micrometres for low power objective lens (x40)

A

25

45
Q

what is the value of one EPU in micrometres for medium power objective lens (x100)

A

10

46
Q

what is the value of one EPU in micrometres for high power objective lens (x400)

A

2.5

47
Q

give ways of improving the microscopy practical

A

use a wet mount
cut finely so you can see individual layer of cells
squash slide to prevent dehydration/distortion

biology (24 decks)

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