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Biology A - Level > Foundations in Biology Module 2.1 -2.3 Microscopy, magnification and calibration > Flashcards

Foundations in Biology Module 2.1 -2.3 Microscopy, magnification and calibration Flashcards

Microscopy

1
Q

What did the cell theory that was developed state

A

Both animal and plant tissues are composed of cells
Cells are the basic unit of all life
Cells only develop from existing cells

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2
Q

What are the benefits of using a light microscope

A

Easily available
Relatively cheap
Can be used out on the field
Observes both living and dead cells prepared specimens
Coloured images

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3
Q

What do the objective lens and eyepiece lens do

A

Increase the magnification of the image and reduce chromatic aberration(distortion)

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4
Q

What is the drawback of light microscopes

A

Very low resolutions so viewing images at high magnifications aren’t helpful because they are blurred

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5
Q

What is a benefit of using a electron microscope

A

more detail of cell ultrastructure

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6
Q

What are the drawbacks of using electron microscopes

A

Very expensive
Can only be used in a carefully controlled environment in a dedicated space
Artefacts can be produced because of very complex sample preparation process
Vacuum required so only dead specimens can be used
Black and white images

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7
Q

What are the two types of electron microscopes

A

Transmission electron microscope(TEM)
Scanning electron microscope (SEM)

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8
Q

How does a TEM produce an image

A

Beam of electrons transmitted through specimen and focused to form image

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9
Q

How does a SEM produce an image

A

Beam of electrons are sent across surface of a specimen and reflected electrons collected

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10
Q

What is the maximum magnification of electron microscopes

A

x500 000

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11
Q

What is the maximum magnification of light microscopes

A

x2000

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12
Q

What is the maximum resolution of a TEM

A

0.5nm

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13
Q

What is the maximum resolution of a SEM

A

3-10nm

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14
Q

What dimension of images does SEM produce

A

3D image which shows valuable information about the appearance of different organisms

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15
Q

What are the 4 types of light microscope sample preparation

A

Dry mount
Wet mount
Squash slides
Smear slides

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16
Q

Method of Dry mount

A

solid specimens viewed whole or cut into thin slices with a sharp blade
Specimen placed on the centre of the slide
Coverslip placed on top of specimen

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17
Q

When solid specimen is cut into thin slices what is this process called

A

Sectioning

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18
Q

What are examples of Dry mount (whole)

A

hair, pollen, dust and insect parts

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19
Q

What are examples of Dry mount ( slices)

A

muscle tissue and plants

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20
Q

Method of Wet mount

A

specimen is suspended under a liquid and coverslip is placed over specimen at an angle

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21
Q

What are the examples of liquids used as an suspension for Wet mount

A

water and an immersion

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22
Q

Method of Squash slides

A

Wet mount prepared
Lens tissue used to gently press down coverslip

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23
Q

What is a potential prevention of damage to coverslip when producing a Squash slide

A

Squash specimen between 2 microscope slides

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24
Q

Squash slides a good technique for what samples

A

Soft samples

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25
Q

Examples of squash slides

A

root tip which is used to observe cell division

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26
Q

Method of smear slides

A

Use the edge of the slide to smear the sample
Thin, even coating created on another slide
Place coverslip over specimen

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27
Q

Example of smear slide

28
Q

Specimens that are illuminated by white light like a light microscope, the images often have

A

low contrast

29
Q

What limits the resolution of light microscopes

A

the wavelength of light and diffraction of light as it passes through sample

30
Q

Definition diffraction

A

bending of light as it passes close to the edge of an object

31
Q

Cytosol (cytoplasm) of cells and other structures are usually

A

Transparent

32
Q

What does stains increase on cells

A

Contrast as different components within the cell take up stains to different degrees

33
Q

What does an increase in contrast allow

A

components to become more visible so they can be identified

34
Q

Method of preparing a sample for staining

A

Place sample on slide and leave to air dry
Heat-fixed by passing through a flame
Specimen adheres to microscope slide and will take up stains

35
Q

Name two positively charged dyes

A

Crystal violet and methylene blue

36
Q

What are the dyes crystal violet and methylene blue attracted to

A

negatively charged materials in cytoplasm resulting in staining of cell components

37
Q

Name two negatively charged dyes

A

Nigrosin and congo red

38
Q

What do the dyes nigrosin and congo red cause in the cell

A

repulsion of negatively charged cytoplasm

39
Q

Name the technique is taking place when dyes stay out of cells, leaving them unstained, allowing them to stand out against the stained background

A

Negative stain technique

40
Q

What does differential staining do

A

distinguishes between two types of organisms that would otherwise be hard to identify.
As well as differentiates between different organelles of a single organism within a tissue sample

41
Q

Why is the gram staining technique used

A

Separate bacteria into two groups:
- Gram positive bacteria
- Gram negative bacteria

42
Q

Method of the gram stain technique

A
  • Crystal violet added to bacterial specimen on slide
  • Iodine applied which fixes the dye
  • Slide washed with alcohol
  • Gram positive bacteria - retain stain and gram negative bacteria lose stain
  • Safranin dye applied - making bacteria appear red
43
Q

Gram stain technique: once slide washed with alcohol what happens to the two groups of bacteria

A
  • Gram positive bacteria - retain the crystal violet stain
  • Gram negative bacteria - have thinner cell walls so they lose crystal violet stain
44
Q

What colour is crystal violet dye

A

Blue/purple under microscope

45
Q

What colour is safranin dye

46
Q

What is safranin dye in gram stain technique

A

It is a counterstain

47
Q

What is gram positive bacteria susceptible to and what this cause

A

Antibiotic penicillin - inhibits the formation of cell walls

48
Q

Why is gram negative bacteria not susceptible to penicillin

A

They have thinner cell walls than gram positive cells

49
Q

What is the use of the acid-fast technique

A

differentiate species of Mycobacterium from other bacteria

50
Q

Method of acid-fast technique

A
  • Carbolfuchsin dye carried into cells by a lipid solvent
  • Cells washed with dilute acid-alcohol solution
    Result:
    -Mycobacterium not affected by acid-alcohol so retains the carbolfuchsin stain
    -Other bacteria lose stain and are exposed to the methylene blue stain which is blue
51
Q

What is the colour of the carbolfuchsin dye

A

Bright red

52
Q

What are the 4 parts of the production process of pre-prepared slides

A

Fixing
Sectioning
Staining
Mounting

53
Q

What happens in the fixing part of the production of pre-prepared slides

A

Chemicals, like formaldehyde are used to preserve specimens in as near-natural a state as possible

54
Q

What happens in the sectioning part of the production of pre-prepared slides

A

Specimens are dehydrated with alcohols and then placed in a mould with resin/wax to form a hard block
The hard block is sliced thinly with a microtome

55
Q

What happens in the staining part of the production of pre-prepared slides

A

Specimens often treated with multiple stains to show different structures

56
Q

What happens in the mounting part of the production of pre-prepared slides

A

Specimens are then secured to a microscope slide and a coverslip is placed on top

57
Q

What features make a good scientific drawing

A
  • Title
  • Magnification
  • Sharp pencil for drawings and labels
  • White/unlined paper
  • At least half the paper provided
  • Smooth/continuous lines
  • No shading
  • Clearly defined structures
  • Correct proportions
  • Label lines parallel to top of the page
  • Label lines - no crossing and no arrow heads
58
Q

Define magnification

A

how many times larger the image is than the actual size of the object viewed

59
Q

Define resolution

A

ability to distinguish between two points which are close together on an object

60
Q

What is the magnification formula

A

magnification = image size/actual size

61
Q

Measurements from metres - nm

A

m x1000 = mm x1000= um x1000 = nm
nm/1000 = um/1000 = mm/1000 = m

62
Q

Features of an eyepiece graticule

A
  • Glass disc
  • scale of 1-100
  • no units
  • remains unchanged under different objective lens
  • Relative size of divisions increase as objective lenses increase
63
Q

Feature of a stage micrometre

A
  • microscope slide
  • Very accurate scale in micrometre
  • 100 divisions = 1mm
  • 1 division = 10um
  • 1/100 = 0.01mm
64
Q

Calculation of 1 graticule division

A

no of micrometres/no of graticule division

65
Q

How to calculate actual size of a specimen with after calibration

A

graticule division x magnification factor

66
Q

Define artefact

A

A visibile structural detail caused by processing the specimen and not a feature of the specimen.
- found on both light and electron microscopy

Biology A - Level (11 decks)

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