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Biology Module 2 > 2.1-2.3 Microscopy > Flashcards

2.1-2.3 Microscopy Flashcards

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1
Q

When was the first type of microscope developed?

A

16th Century

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2
Q

State the 3 rules of Cell Theory.

A

-Both plant and animal tissue is composed of cells
-Cells are the basic unit of all life
-Cells only develop from existing cells.

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3
Q

What can microscopes be used for?

A

Observing living and dead specimens.

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4
Q

What are the names of the two lenses in a compound light microscope?

A

Eyepiece lens and objective lens.

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5
Q

What is the difference between a light microscope and a compound light microscope?

A

There is significantly less chromatic aberration and higher magnification in a compound light microscope.

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6
Q

What term should you use instead of “clarity” when discussing microscopy?

A

“Distinction” and “resolution”

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7
Q

With increased resolution, what do objects become?

A

“Visibly distinct”, more detail can be seen

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8
Q

What will the method chosen to prepare a sample for examination by a light microscope depend on?

A

The nature of the specimen and the resolution that is desired.

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9
Q

What is a dry mount?

A

-Specimens are viewed whole or cut into thin slices with a sharp blade (sectioning).
-Specimen is placed on the slide and a cover slip is placed over the sample.

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10
Q

Give examples of things that can be observed using a dry mount.

A

Hair, pollen, insect parts, muscle tissue, plants.

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11
Q

What is the name of the mount/slide whereby solid specimens are viewed whole or cut into thin slices?

A

Dry mount.

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12
Q

What is a wet mount?

A

-Specimens are suspended in a liquid such as water or an immersion oil.
-Cover slip is placed on at an angle

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13
Q

In a wet mount, why is the cover slip placed on at an angle?

A

To reduce air bubbles and artefacts.

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14
Q

What is the name of the slide/mount whereby specimens are suspended in a liquid?

A

Wet mount.

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15
Q

Give examples of specimens that can be viewed using a wet mount.

A

Aquatic samples, living organisms

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16
Q

What is a squash slide?

A

-A wet mount is first prepared, then a lens tissue is used to gently press down the cover slip (a microscope slide can also be used instead of a cover slip to prevent damage)

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17
Q

What can squash slides be used for?

A

Soft samples, for example root tips can be squashed to look at cell division.

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18
Q

What is the name of the mount/slide whereby a lens tissue is used to gently press down the cover slip?

A

Squash slide.

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19
Q

What is a smear slide?

A

-The edge of a slide is used to smear the sample to create a thin even coating on another slide
-A cover slip is then placed over the sample

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20
Q

What can smear slides be used for?

A

Samples of blood, to see all the cells.

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21
Q

What is the name of the mount/slide whereby an edge of a slide is used to spread the sample to create a thin even coating on another slide?

A

Smear slide.

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22
Q

What are the benefits of wet mounts?

A

-Can be used for hiehger magnification
-Can allow you to observe behaviour of animals
-Greater resolution because the liquid refracts light
-Can observe natural colour and mobility patterns of animals

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23
Q

What are the problems with wet mounts?

A

-Greater chance of artefacts being produced (eg air bubbles)
-Slides tend to dry out under the light of the microscope.

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24
Q

What are the benefits of dry mounts?

A

It is easy to prepare slides

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25
Q

What are the problems with dry mounts?

A

-Mounts are temporary unless you seal them
-It is harder to see more intricate structures.

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26
Q

Why do specimens need to be thin for sample preparation?

A

So that light can pass through it and form an image

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27
Q

What is an artefact?

A

Something observed in a scientific investigation that is not naturally present but occurs as a result of the investigative procedure.

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28
Q

What is brightfield microscopy?

A

The sample is illuminated from below with white light and observed from above.

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29
Q

What is wide-field microscopy?

A

The whole sample is illuminated at once.

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30
Q

Why do we stain samples in microscopy? (Short answer)

A

-Stains increase the contrast of specimens because the different components in the cells absorb the stains to different degrees.
-The increase in contrast allows components to become visible so they can be identified.

31
Q

Why is it difficult to see specimens under a microscope without staining them first?

A

-Because cells do not absorb much lught
-The cytosol (aqueous interior) of cells, and other cell structures, are often transparent.

32
Q

How do you prepare a sample for staining?

A

-First place it on a slide and allow it to air dry
-Heat-fix it by passing it through a flame
-The specimen will now adhere to the slide and take up stains.

33
Q

What is differential staining?

A

Using specific stains to distinguish different types of cell

34
Q

Describe the process of FIXING in microscopy.

A

Formaldehyde is used to preserve the specimen

35
Q

Describe the process of SECTIONING in microscopy.

A

Specimens are dehydrated and placed in a wax mould, then thinly sliced sith a microtome.

36
Q

Describe the process of STAINING in microscopy.

A

Specimens are often treated with multiple stains to show different structures

37
Q

Describe the process of MOUNTING in microscopy.

A

The specimens are secured to a microscopy slide and a cover slip is placed on top.

38
Q

Give two examples of negatively charged dyes

A

Nigrosin and Congo red.

39
Q

Explain the process of the NEGATIVE STAIN TECHNIQUE.

A

Negatively charged dyes are repelled by the negatively charged cytosol so they stay outside of the cell, making the unstained cells stand out against the stained background.

40
Q

Give two examples of positively charged dyes.

A

Crystal Violet or Methylene Blue

41
Q

Explain the process of the POSITIVE STAIN TECHNIQUE.

A

Positively charged dyes are attracted to the negatively charged materials in the cytoplasm (eg cytosol), which leads to the staining of the cell components.

42
Q

What is Gram stain technique?

A

Used to separate bacteria into Gram-positive and Gram-negative categories.

43
Q

Describe the process of the Gram stain technique

A

-Crystal violet dye is first applied to a bacteria specimen on a slide, then iodine (which fixes the dye),
-The slide is then washed with alcohol

44
Q

What is the result of a Gram-positive bacteria having the Gram stain technique applied onto it?

A

-After the wash with alcohol, the bacteria retain the crystal violet stain and appear blue or purple under a microscope

45
Q

What are Gram-positive bacteria?

A

A type of bacteria that have a thick cell-wall, and are susceptible to Penicillin (which inhibits the formation of cell walls)

46
Q

What is the result of a Gram-negative bacteria having the Gram stain technique applied onto it?

A

-After the wash with alcohol, the bacteria lose the stain.
-They are then stained with a “counterstain” called safranin dye, which will make the bacteria appear red or pink.

47
Q

What is the counterstain used in Gram stain technique?

A

Safranin dye

48
Q

What are Gram-negative bacteria?

A

Bacteria with a thin cell wall that aren’t susceptible to penicillin

49
Q

What is Acid Fast Technique?

A

Used to differentiate species of mycobacterium from other bacteria.

50
Q

Describe the process of Acid Fast Technique

A

-A lipid solvent is used to carry carbolfuchsin dye into the cells being studied.
-Cells are washed with a dilute acid-alcohol solution
-Mycobacterium are not affected by the acid-alcohol and retain the stain, which is bright red.
-Other bacteria lose the stain and are exposed to a methylene blue stain

51
Q

What dye is used in Acid Fast Technique?

A

Carbolfuchsin dye

52
Q

What are the cells washed with after the dye is applied in Acid Fast Technique?

A

A dilute acid-alcohol solution

53
Q

If mycobacterium is found when using the Acid Fast Technique, what will happen?

A

The mycobacterium will not be affected by the acid-alcohol, and retain the carbolfuchsin stain which is bright red.

54
Q

If mycobacterium is NOT found when using the Acid Fast Technique, what will happen?

A

-The bacterium will be affected by the acid-alcohol, lsoing the carbolfuchsin stain.
-They will then be exposed to a methylene blue stain.

55
Q

What do we use to stain starch?

A

Iodine.

56
Q

Define “Magnification”

A

The number of times larger an image is compared to the real size of an object

57
Q

Define “Resolution”

A

The ability to distinguish between two separate points.

58
Q

Define “Empty Magnification”

A

When you magnify an image to make it larger, but it does not appear more defined

59
Q

Describe the advantages of Light Microscopes

A

-Cheap, easily accessible, easy to use
-Natural colour of material can be observed
-Living organisms can be observed
-Preparation is quick and simple

60
Q

Describe the disadvantages of Light Microscopes

A

-Low resolving power
-Only magnifies objects up to 1500x

61
Q

Describe the advantages of Electron Microscopes in general

A

-Can see detail of organelles
-Much better resolution than light microscopes
-Magnifies objects more than 500,000x

62
Q

Describe the disadvantages of Electron Microscopes in general

A

-No colour
-Very large and must be operated in special rooms
-Expensive
-Damages the specimen
-Preparation of material is lengthy and complex.

63
Q

Describe how a Transmission Electron Microscope works.

A

Fires a beam of electrons though the specimen and produces a 2D image

64
Q

Describe the resolving power and maximum magnification of a Transmission Electron Microscope.

A

Resolution: 0.2nm, Magnification 500,000x

65
Q

Describe how a Scanning Electron Microscope works.

A

Fires a bean of electrons across the surface of a specimen and produces a 3D image.

66
Q

Describe the resolving power and maximum magnification of a Scanning Electron Microscope.

A

Resolution: 0.5-4nm, Magnification = 100,000x

67
Q

How does an Electron Microscope work?

A

-A beam of electrons witha wavelength of less than 1nm is used to illustrate the specimen,
-The inside of an electron microscope is a vacuum to ensure the electron beams travel in straight lines.
-Because of the vacuum, specimens need to be treated in very specific ways.

68
Q

Why do specimens need to be treated in very specific ways for Electron Microscope scanning?

A

Because the inside of an electron microscope is a vacuum.

69
Q

Describe how Laser Scanning Confocal Microscopy works.

A

-Uses lasers to enable the reconstruction of three-dimensional objects
-Shows sets of images obtained at different depths (sectioning)
-Can show fluorescent dyes and tags

70
Q

Describe how to prepare a specimen for electron microscopy

A

-Fixation of the specimen using chemicals or freezing
-Stain with heavy metals
-Dehydrate with solvents
-Samples for TEM will be set in resin and may be stained again
-Samples for SEM may be fractured to expose the inside and will then need to be coated with heavy metals.

71
Q

What is a graticule?

A

A specialised piece of glass inserted into the microscope, that features a calibrated grid or scale etched into its surface

72
Q

What are the two types of graticules?

A

Eyepiece graticule and stage graticule

73
Q

What is the difference between the two types of graticules?

A

-The eyepiece graticule has regular divisions that need to be calibrated for each magnification
-The stage graticule shows true lengths

74
Q

What is 1 stage micrometer unit equal to?

A

10 micrometers

Biology Module 2 (9 decks)

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