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AS Biology > Microscopy > Flashcards

Microscopy Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what is cell theory?

A

The idea that all living things are made of cells

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2
Q

How do cells develop?

A

from existing cells (mitosis, meiosis)

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3
Q

what are plants and animals made up of?

A

Tissues, which are made up of cells

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4
Q

what is another name for the eyepiece lens?

A

The ocular lens

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5
Q

What do the objective lenses do?

A

They increase the magnification at different intensities

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6
Q

What does the slide do?

A

It holds the specimen

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7
Q

What does the light source for a microscope include/

A

A lamp or a mirror

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8
Q

Why does the specimen need to be thin/

A

So that light can pass through it

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9
Q

Which magnifies an image first - the objective lens or the eyepiece lens?

A

The objective lens

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10
Q

What does staining the specimen do?

A

Increase the contrast, as light microscopes have low magnification and low resolution

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11
Q

What does crystal violet do?

A

It stains cell walls purple

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12
Q

What does methylene blue do?

A

stains the nuclei in animal cells to give contrast(stains blue)

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13
Q

What does Congo red do?

A

it’s a negative stain that isn’t taken up by the cell but provides a contrast between the cell and the background

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14
Q

What are the 2 types of electron microscope?

A

The scanning electron microscope and the transmission electron microscope

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15
Q

What does the scanning electron microscope do?

A

Focuses a beams of electrons across an object in order to produce an image of the objects surface

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16
Q

What does the transmission electron microscope do?

A

focuses a beam of electron through a specimen(interior)

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17
Q

What does a laser scanning microscope do?

A

Use laser beams to scan a dyed specimen . When the dye is scanned, it will give off light which is focused through a pinhole onto a detector to produce a 3D image.
This ensures any out of focus light is blocked producing a clear image. This allows the looking of objects that are either thick or of different depths.

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18
Q

What is the equation for magincation?

A

Magnification = image size / actual size

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19
Q

What is the magnification?

A

How much bigger an image is than the specimen

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20
Q

1m = how many mm?

A

1000mm

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21
Q

1mm = how many um?

A

1000um

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22
Q

1um = how many nm?

A

1000nm

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23
Q

What is the resolution?

A

The ability to clearly distinguish 2 points that are close together

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24
Q

What are some things than need to be included in a microscopic diagram/

A

Scale, magnification, labels, takes up half the page, annotations, title

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25
Q

What is the wavelength of an electron beam?

A

0.004nm

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26
Q

How many times shorter is an electron wavelength than a light wavelength?

A

100, 000 times shorter

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27
Q

How good is the resolution of an electron microscope?

A

It allows you to distinguish between objects that are 0.2nm apart.

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28
Q

How many times greater is the resolution of an electron microscope than the resolution of the human eye?

A

500 000 times greater

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29
Q

What type of image is produced using a Transmission electron microscope?

A

A 2D image

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30
Q

What type of image is produced using a scanning electron microscope?

A

A 3D image

31
Q

What are the advantages of using an electron microscope?

A

-The resolution is 0.2nm (1000x more than the light microscope),

-More detailed image of the structures inside the cell,

-The SEM produces 3D images that can reveal the detail of the contours and cellular or tissue arrangements (not possible in a light microscope)

32
Q

What are the disadvantages of using an electron microscope?

A

Electrons are deflected by the molecules in the air, so samples have to be produced in a vacuum, they’re extremely expensive, Preparing samples for an electron microscope requires a high level of skill and training

33
Q

What is a stage graticule?

A

A microscopic ruler on a special slide. This ruler is 10mm long and divided into 100 divisions. Each is 0.01mm or 10 micrometres.

34
Q

Step by step, how do you use graticules?

A

1) Place a stage micrometer on the stage of the microscope.
2) Line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.
3) Count the number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer.
4) Calculate the distance in micrometres of one division on the eyepiece graticule.

35
Q

What’s another name for a graticule?

A

A micrometer

36
Q

What does Haematoxylin do?

A

It stains RNA/DNA a purple/blue colour

37
Q

What does Acetic orcein do?

A

binds to DNA and stains
chromosomes dark red

38
Q

What does Eosin do?

A

stains cytoplasm dark red or pink

39
Q

What does iodine do?

A

Stains starch blue black (violet under a microscope)

40
Q

What does iodine in potassium iodide solution do?

A

stains cellulose yellow

41
Q

What is a wet mount used for?

A

viewing a variety of live specimens, such as aquatic animals

42
Q

What is a dry mount used for?

A

used for specimens such as hairs, parts of insects, pollen, parts of flowers etc.

43
Q

What is the image recorded with an electron microscope called?

A

An electron micrograph

44
Q

What does the course adjustment knob do?

A

It roughly brings the specimen into focus

45
Q

What does the fine adjustment knob do?

A

It finely tunes the focus

46
Q

Is it true that the human eye can only distinguish objects that are 0.1mm apart?

A

Yes

47
Q

What type of image do light microscopes produce?

A

A 2D image

48
Q

What is the resolution of a light microscope?

A

200nm

49
Q

What is the magnification of a light microscope?

A

X 2000

50
Q

What are the steps in preparing a slide?

A

1) Stain the sample with an appropiate dye
2) Mount the sample on the slide
3) Place a cover slip carefully on the slide, avoiding air bubbles

51
Q

What is methylene blue?

A

An all purpose stain-usually used to stain the DNA blue

52
Q

What are the steps in using a light microscope?

A

1)Clip the slide onto the stage
2)Select the lowest-powered objective lens
3) Use the coarse adjustment knob to move the objective lens to just above the slide.
4) . 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. Note: always adjust the focus by moving the lens away from the slide – this prevents you from moving the lens too close to the slide and breaking it
5) If a higher magnification is needed, swap to a higher-powered objective lens and refocus (repeat steps 3-4).

53
Q

What are the advantages of TEM microscopes?

A
  • they give a high resolution image
  • they allow the internal structures within a cell to be viewed
54
Q

What are the disadvantages of TEM microscopes?

A
  • they can’t be used to observe live specimen
  • they can only be used with very thin specimens of the objects being observed
  • they can’t produce a coloured image
    -The lengthy treatment required to prepare specimens means that artefacts can be introduced (artefacts look like real structures but are actually the results of preserving and staining)
55
Q

What are the advantages of an SEM microscope?

A

-Can be used on thick/3D specimens
-They allow the external 3D structure of specimens to be observed

56
Q

What are the disadvantages of an SEM microscope?

A
  • they give lower resolution images in comparison to Team microscopes
    -Can’t be used to observe live specimens
    -Don’t produce coloured images
57
Q

What are the advantages of laser microscopes?

A

-Give high resolution and magnification
-Can be used on thick/3D specimens
-Allows the internal structures of specimens to be observed

58
Q

What are the disadvantages of laser microscopes?

A

-Obtaining an image is a long and slow process
-Laser microscopes can potentially cause photodamage to cells
-Laser microscopes are expensive and large

59
Q

What are the advantages of light microscopes?

A

-Inexpensive to buy and use
-Easy to carry around
-Can be used to view both living and dead organisms
-The original colour of the specimen can be viewed

60
Q

What are the disadvantages of light microscopes?

A

-They have a low magnification and resolution
-It’s hard to view smaller internal structures of the cell, such as ribosomes
-Can’t operate in the dark, as they need a light source

61
Q

How can some tissue samples be treated with chemicals?

A

-This involves fixing the specimen using formaldehyde (preservative), dehydrating it using a series of ethanol solutions, impregnating it in paraffin/resin for support then cutting thin slices from the specimen using a microtome.

-Then, the paraffin is removed from the slices/specimen, a stain is applied and the specimen is mounted using a resin and a coverslip is applied

62
Q

What is formaldehyde?

A

A preservative

63
Q

What can specimens be frozen in?

A

carbon dioxide or liquid nitrogen. They can then be cut into thin slices using a cryostat and placed on a slide with the stain added.

64
Q

What objective lens should be used first when using an optical microscope?

A

A low power objective lens

65
Q

Why should a low power objective lens be used first when using an optical microscope?

A

Because it’s easier to find what you’re looking for in the field of view and also to prevent damage to the lens or coverslip in case the stage has been raised too high

66
Q

What can happen to thin layers of material placed on slides?

A

They can dry rapidly

67
Q

How can the dehydration of tissue be prevented?

A

By adding a drop of water to the specimen (beneath the coverslip)

68
Q

What 3 things can be done to resolve the issue of unclear or blurry images?

A

1)Switch to the lower power objective lens and try using the coarse focus to get a clearer image

2)Consider whether the specimen sample is thin enough for light to pass through to see the structures clearly

3)There could be cross-contamination with foreign cells or bodies

69
Q

When using TEM’s, why must the specimen be stained?

A

In order to absorb the electrons. Unlike light, electrons have no colour. The dyes used for staining cause the tissues to show up black or different shades of grey

70
Q

Why are heavy metal compounds often used as dyes for electron microscopy?

A

Because they absorb electrons well

71
Q

What are some examples of heavy metal compounds?

A

Osmium tetroxide and ruthenium tetroxide are examples

72
Q

What are the colours in electron micrographs a result of?

A

Colours are added to the image using an image-processing software - not because of natural colour or staining

73
Q

Use

A

AS Biology (15 decks)

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