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Biology > 2.1.1 Microscopy > Flashcards

2.1.1 Microscopy Flashcards

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1
Q

What are the 4 types of microscope?

A

• Light microscope
• transmission electron microscope [TEM]
• scanning electron microscope [SEM]
• laser scanning confocal microscope (type of light microscope)

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2
Q

How does a Scanning Electron microscope work?

A

A beam of elections is sent across the surface of the specimen and the reflected electrons are collected to form the image

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3
Q

Does a scanning electron microscope produce a 2D or 3D image?

A

SEM produces a 3D image

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4
Q

Does a SEM give a higher or lower resolution than a TEM

A

SEM produces lower resolution images than TEM

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5
Q

How does a Transmission electron microscope work?

A

Use electromagnets, a beam of electrons pass through the specimen and focussed to produce the image.
Denser parts of the specimen absorb more electrons, so they look darker.

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6
Q

Do transmission electron microscopes have a higher or lower resolution than SEM

A

Transmission electron microscopes have a very high resolution

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7
Q

How does a laser scanning confocal microscope work?

A

• Use laser beams,
• A single spot of light is moved across the sample (point illumination).
• Specimen is dyed with fluorescent dye
• Laser causes dyed parts to fluorescence - give off light
• light filtered through pinhole onto detector
• pinhole means out of focus light is blocked, producing a clear image.

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8
Q

Does a laser scanning confocal microscope produce a 3D or 2d image

A

Laser scanning confocal microscope images can be both 2D and 3D

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9
Q

Properties of light microscope:
Uses…
Magnification
Resolution
Dead / alive specimen

A

Light microscope:
Uses light radiation and glass lenses to focus
Magnification x1500 - x2000
Resolution 200nm / 0.2um
No vacuum - specimens can be alive/dead
Stained with eyes
Viewed with eye
View whole cells or tissues

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10
Q

Properties of scanning electron microscope:
Uses…
Magnification
Resolution
Dead / alive specimen
Stained with…
Viewed with…
Image colour…

A

• Uses electrons from electron gun, focused by electromagnets
• magnification x100 000 -x500 000
• resolution 3-10nm / 0.002um
• need vacuum - dead specimen
• stained with heavy metals
•Viewed on computer
• B&W

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11
Q

Properties of transmission electron microscope:
Uses…
Magnification
Resolution
Dead / alive specimen
Stained with…
Viewed with…
Image colour…

A

Uses electron from electron gun, focussed by electromagnets
•Magnification - x500 000 - x2000 000
•Resolution - 0.2 - 0.5nm / 0.0002um
• need vacuum - dead specimen
• stained with heavy metals
• Viewed on computer
• B&W

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12
Q

Features of light microscope images

A

• Light background
• 2D
• Variety of colours
• Show details larger than 200nm only
• Large organelles only - (nuclei, vacuole, cholroplasts, mitochondria) / parts of organisms/whole cells
• observing small organisms

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13
Q

Features of laser scanning confocal microscope

A

• 2D computer can make 3D
• black background
• limited colour
• observing stained structures within cells/whole cells

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14
Q

Features of transmission electron microscope

A

• Always 2D
• only grayscale unless false colour
• v high magnification
• high resolution - grainy image
• observing organelles within cells or whole cells

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15
Q

Features of scanning electron microscope

A

• 3D (inside and outside)
• outside surfaces
• greyscale/ false colour

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16
Q

Identify the type of microscope used when shown a photomicrograph

A

Light: light background
TEM: false colour, v high resolution
SEM: black background, false colour, 3D looking, v high resolution
Laser scanning confocal: black black ground, limited colour

17
Q

Timeline showing development of microscope

A

Romans experiment with glass lenses

13th century invention of spectacles

15th century century telescope

1609 Galileo Galilei first ‘thing’ to be called microscope (compound light)

18
Q

How did the development of the microscope intifuence scientific thinking.

A

Allowed cells to be observed - disproved spontaneous generation
Allowed theories to be presented and disproved then replaced when technology improves

19
Q

Describe and explain the characteristics of a good slide preparation

A

No artefacts
Thin
Transparent
Clean slides + coverslips
Good contrast
Cells spread out with limited overlap
Appropriate vowme of liquid

20
Q

Why do slide preparations need to be thin

A

To let light through
Individual cells can be identified

21
Q

Why is staining useful for light microscopy

A

Many specimens are transparent
Some parts of the object take up more dye
Creates a contrast in colour or intensity between objects and their surroundings

Different stains bind to different molecules

22
Q

What is a polychromatic stain?

A

Polychromatic stains show different colours with different molecules

23
Q

Can more than one stain be used at once?

A

Yes, because they bind to different molecules

24
Q

Give 4 examples of stains

A

Methylene blue
eosin
Toluidine blue
Iodine in potassium iodide

25
Q

What do eosin, methylene blue, Toluidine blue
Iodine in potassium iodide stain ?

A

Methylene blue - DNA
Eosin- cell cytoplasm

• Toluidine blue - phloem - red, xylem - blue, DNA-blue
• Iodine in potassium iodide - starch blue / black

26
Q

What properties does a stain need to have to be use for light microscopy?

A

Differential staining - stain some objects and not others
↳ contrast visible
Intense colour - v. Small amount of biological material but has to be visible

27
Q

What is the formula for magnification ?

A

Magnification = image size / actual size

28
Q

How to convert from
mm —> um —> nm

A

mm —> um —> nm
x1000 x1000

29
Q

Define resolution

A

The ability to distinguish between 2 separate points

30
Q

Define magnification

A

Number of times larger the image is compared to the object

31
Q

What is the difference between magnification and resolution?

A

Magnification is enlargement not always increased detail
Resolution is distance
Magnification has no units

32
Q

Resolution and max magnification of all the microscopes

A

Light : 200nm and 1500-2000x
SEM: 3-10nm and 100,000 - 500,000x
TEM: 0.2nm and 500,000 - 2,000,000

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