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BH4 > Ch 2 > Flashcards

Ch 2 Flashcards

1
Q

Regardless of the type of microscope being used, what 3 elements are always needed to form an image?

A
  1. a source of illumination
  2. a specimen to be examined,
  3. a system of lenses that focuses the illumination on the specimen and forms the image
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2
Q

In a light system what is the source of illumination and system of lenses that focuses the illumination on the specific and forms the image?

A
  • source of illumination: visible light

- system of lenses: series of glass

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3
Q

In a light system what is the source of illumination and system of lenses that focuses the illumination on the specific and forms the image?

A

illumination: beam of electrons emitted by a heated tungsten filament

system of lenses: series of electromagnets.

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4
Q

How is the image formed from light microscopy viewed

A

either viewed directly through an eyepiece or focused on a detector, such as photographic film or an electronic camera.

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5
Q

How is the image formed from electron microscopy viewed

A

electron beam is focused on either a fluorescent screen or photographic film, or it is digitally imaged using a detector

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6
Q

What is a wavelength

A

Distance from crest of 1 wave to crest of next wave

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7
Q

What does the rope analogy demonstrate

A

The ability of an object to perturb a wave’s motion depends crucially on the size of the object in relation to the wavelength of the motion
- wavelength of light source sets limit on how small an object can be seen

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8
Q

Do photons or electrons have shorter wavelengths

A

electrons

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9
Q

What is interference

A

The process by which 2 or more waves combine to reinforce or cancel one another, producing a wave equal to the sum of the 2 combining waves

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10
Q

What is diffraction

A

image that you see when you look at a specimen through a series of lenses is really just a pattern of either additive or canceling interference of the waves that went through the lenses,

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11
Q

What two fundamental properties do light and electron microscopy have in common

A

Focal length and angular aperture

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12
Q

What is focal length

A

distance btwn midline of lens & point at which rays passing thru lens converge to a focus

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13
Q

What determines the focal length

A

determined by the index of refraction of the lens itself, the medium in which it is immersed, and the geometry of the lens.

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14
Q

What unit is focal length measured in

A

meters

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15
Q

What unit is the lens magnifying strength measured in

A

Diopters

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16
Q

What is angular aperture

A

half-angle alpha of the cone of light entering the objective lens of the microscope from the specimen AKA how much of the illumination that leaves the specimen actually passes through the lens

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17
Q

What determines sharpness of interference pattern & thus ability of lens to convey info about specimen?

A

angular aperture

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18
Q

in best light microscopes what is the degree of angular aperture

A

70 degrees

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19
Q

What is resolution

A

minimum distance 2 points can be apart & yet still remain identifiable as separate points when viewed thru microscope

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20
Q

the higher the resolution, the ___ the objects that can be distinguished using a particular lens

A

smaller

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21
Q

What 3 factors govern resolution

A

wavelength of light used to illuminate specimen, angular aperture, refractive index of medium surrounding specimen

22
Q

What is refractive index

A

measure of the change in the velocity of light as it passes from one medium to an- other.

23
Q

What does the constant 0.61 represent

A

the degree to which image points can overlap and still be recognized as separate points by an observer

24
Q

What is n sin alpha

A

numerical aperture

25
Q

What is the Abbe eqn

A

r = 0.61 lambda/ NA

26
Q

is smaller or larger r better?

A

smaller

27
Q

Unit for r?

A

nm

28
Q

The larger the angular aperture the more ___ info the lens can transmit

A

more

29
Q

What is useful magnification

A

.

30
Q

Greatest magnification that can be achieved with a light microscope is ____ x the numerical aperture of the lens being used

A

1000 x

31
Q

Theoretical limit of resolution of electron microscopes

A

0.002nm

32
Q

What prevents the electron microscope from achieving the theoretical limit of resolution of 0.002nm

A

electromagnets produce considerable distortion when the angular aperture is more than a few tenths of a degree. aka numerical aperture is smaller than light microscope

33
Q

What is the PRACTICAL limit of resolution of electron microscope

A

2nm

34
Q

What is a compound microscope

A

light microscope that uses several lenses in combo

35
Q

What are condenser lenses

A

direct light toward specimen mounted on glass slide

36
Q

What is stage

A

Where specimen is placed on

37
Q

what are objective lens

A

forms primary image

38
Q

what are ocular lens/eyepiece

A

enlarges primary image

39
Q

what are intermediate lens

A

positioned btwn objective and ocular lens to further enlarge image

40
Q

how do calculate overall magnification of image

A

multiply enlarging powers of objective lens, ocular lens, and intermediate lens

41
Q

Characteristics of brightfield microscopy

A
  • specimen must be dead
  • only specimens possessing colour or other property that affects amount of light that passes thru (or else must be stained)
42
Q

Characteristics of phase-contrast microscopy

A
  • improves contrast w/out sectioning or staining by exploiting differences in thickness & refractive index of various regions of cells being examined
  • converts phase differences into alterations in brightness
43
Q

What is a phase plate

A

optical material inserted into the light path above the objective lens.

44
Q

How does DIC (differential interference contrast microscopy diff from phase-contrast microscopy

A

DIC is more sensitive cause employs special prism to split the illuminating light beam into 2 separate rays. Then 2 beams recombined, any changes that occurred in the phase of one beam as it passed through the specimen cause it to interfere with the second beam.

45
Q

optical components required for DIC microscopy

A

PAP - polarizer, an analyzer, and a pair of Wollaston prisms.

46
Q

How does Hoffman modulation contrast increase contrast

A

increases contrast by detecting optical gradients across a transparent specimen using special filters and a rotating polarizer

47
Q

What is fluorescence

A

process that begins with the absorption of light by a molecule and ends with emission of light with a longer wavelength

48
Q

emitted photon is always of ___ energy (____ wavelength) than the original photon that was absorbed.

A

less energy, long wavelength

49
Q

Characteristics of fluorescence microscopy

A
  • light microscopy that employs light to excite fluorescence in specimen
50
Q

What is a excitation filter

A

placed btwn the light source & rest of light path that transmits only light of a particular wavelength

51
Q

what is a dichroic mirror

A

reflects light below certain wavelength & transmits lights above certain wavelength, deflects incoming light toward objective lens which focuses light onto specimen

52
Q

What is immunostaining

A

based on the ability of antibodies to recognize and bind to specific molecules (antigens)

BH4 (9 decks)

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