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Biology A LEVEL > Microscopes > Flashcards

Microscopes Flashcards

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1
Q

What are the 3 main types of microscopes?

A
  • Scanning electron microscope
  • Transmission electron microscope.
  • Optical microscope.
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2
Q

Magnification DEF

A
  • How many times larger an image is compared to the actual object.
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3
Q

Resolution Def

A
  • The ability to distinguish between two points on an image ie amount of detail.
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4
Q

What does the resolution of an image depend on in an electron vs light/ optical microscope?

A
  • Light: depends on wavelength of light (long wavelength of light —> lower resolution.)
  • Electron: wavelength of the beam of electrons (shorter wavelength of electrons –> higher resolution.)
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5
Q

Resolution DEF

A
  • The ability to distinguish between two points on an image.
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6
Q

How does light microscope work?

A
  • Light is condensed to create image.
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7
Q

Advantages of light microscopes.

4 main advantages

A
  • Coloured images.
  • Can view living samples.
  • No risk of artefacts.
  • Simple sample prep
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8
Q

Disadvantages of light microscopes.

give 2

A
  • Lower resolution as light has longer wavelength than a beam of electrons.
  • Lower magnification
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9
Q

How do electron microscopes work IN GENERAL?

A
  • Beam of electrons condensed to create image.
  • Electromagnets are used to condense the beam.
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10
Q

Specifically, how does SEM work?

A
  • Electrons bounce off surface (scatter in different ways depending on the contours) of specimen and are condensed by electromagnets to create image.

() - extra information.

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11
Q

Specifically, how does a TEM work?

A
  • Electrons pass through thin specimen (some absorbed, some pass straight through.)
  • Denser parts (of specimen) absorb more electrons (appear darker.) Parts where electrons gone straight through = white.
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12
Q

Why must specimens under an electron microscope be in a vaccum? What does this explain?

A
  • Because electrons are absorbed by air.
  • This explains why only non-living specimens can be examined.
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13
Q

Because electrons have a shorter wavelength than light, what advantage does this give both electron microscopes?

A
  • Shorter wavelength = higher resolution (allowing internal structures/ smaller organelles to be observed.)
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14
Q

When using SEM, do the specimens need to be as thin as when using a TEM microscope?

A
  • No. Specimens don’t have to be AS thin.
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15
Q

What images are produced by light (optical) microscope and a TEM microscope?

A
  • 2D images.
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16
Q

What images are produced by SEM microscope?

A
  • 3D images.
17
Q

Which microscope allows to see specimen with colour?

A
  • Light
  • Both electron microscopes do not.
18
Q

What is the preparation of a sample like in light microscopes?

A
  • Simple prep
  • Can view live cells.
19
Q

Under which microscope can you view living specimens?

A
  • Under the light/ optical microscope.
20
Q

What is the preparation of samples like under an SEM microscope?

A
  • More complex staining process than light microscope but less than TEM (not as thin specimens need to be used.)

() - extra for clarification.

21
Q

What is the preparation of samples under TEM microscope like (in comparison to the other microscopes?)

A
  • Much thinner specimens/ more time consuming.
  • Complex staining process.
22
Q

What is the disadvantage of SEM and TEM microscopes in terms of artefacts? Advantage of light/ optical?

A
  • Optical: N/A (no artefacts.)
  • SEM: risk of artefacts
  • TEM: highEST risk of artefacts.
23
Q

What are artefacts?

A
  • Observations that appear on micropgraphs due to staining/ preparation that aren’t supposed to be part of the micrograph/ on the cell.
24
Q

Why is there no scale on the eyepiece graticule?

A
  • Divisions on the eyepiece graticule scale will be different depending on magnification used.
25
Q

How do you calibrate the eyepiece graticule?

A
  • Use a stage micrometer (glass slide with a scale on it.)
  • The scale on the stage micrometer is usually 2mm long/ each sub-division worth 10 micrometers.
26
Q

How do you work out the value of each small division on the eyepiece graticule?

A
  • ## Line up the stage micrometer with the eyepiece graticule.
27
Q

When would we need to recalibrate a microscope?

A
  • When changing the magnification.
28
Q

What is the difference between a graticule unit and a smaller division?

A
  • Graticule units: large units on eyepiece graticule.
  • Smaller divisions: the smaller units between graticule units on eyepiece graticule.
29
Q

Which has higher resolution, SEM or TEM?

A
  • TEM has a higher resolution.

Biology A LEVEL (22 decks)

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