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biology > Microscopes > Flashcards

Microscopes Flashcards

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1
Q

What is resolution?

A

Resolution: the ability to distinguish between 2 distinct points clearly. (The clarity of an image)

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2
Q

What is the result of high linear magnification?

A

Higher the linear magnification, the wider and longer the image is compared to the size of the actual object.

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3
Q

What is the result of high resolution?

A

Higher the resolution, the clearer the image.

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4
Q

Advantages of optical (light) microscopes.

A
  • Relatively cheap.
  • Easy to use.
  • Portable (so can be used in filed and laboratories).
  • Views living specimens.
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5
Q

Define photomicrograph.

A

Photomicrograph: a photograph of an image seen using an optical (light) microscope.

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6
Q

What is the magnification formula?

A

Magnification = image size / object size

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7
Q

How does a laser scanning (confocal) microscope work?

A
  • Laser light used to scan an object tagged with fluorescent dye.
  • Laser causes the dye to give off light which is focused onto a detector to a computer.
  • Computer assembles pixels information into 1 image.
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8
Q

Advantages of laser scanning (confocal) microscopes.

A
  • 3D image.
  • Highest resolution of all microscopes.
  • High contrast due to depth selectivity to focus on structures at different depths within the specimen.
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9
Q

Advantages of TEM.

A
  • high resolution so used to look at a range of organelles.
  • Highest magnification of all microscopes.
  • High contrast in image.
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10
Q

What is magnification?

A

Magnification: the number of times larger an image appears compared to the size of the actual object.

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11
Q

How does a transmission electron microscope work?

A
  • The specimen has to be dehydrated and stained with metal salts and placed into a vacuum.
  • electromagnets focus a beam of electron which are then transmitted through the specimen. Some electrons pass through and are focused onto the screen/photographic plate.
  • Denser parts of the specimen absorb more electrons so look more darker in the end image.
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12
Q

Define electron micrograph.

A

Electron micrograph: photograph of an image seen using an electron microscope.

Always in black and white but colour can be added afterwards.

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13
Q

How do scanning electron microscopes work?

A
  • Specimen has to be placed into a vacuum and often coated with a fine film of metal salts.
  • A beam of electrons scanned across the specimen. This knocks off electrons from the specimen which are collected in a cathode ray tube to form an image.
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14
Q

Disadvantages of optical (light) microscopes.

A
  • Low resolution so usually used to look at tissues or whole cells due to short wavelength.
  • Produces a 2D image.
  • Specimens have to be thin and transparent.
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15
Q

Total magnification formula.

A

Total magnification = magnifying power of objective lens X magnifying power of eyepiece lens

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16
Q

Advantages of SEM.

A
  • Image can be 3D
  • High resolution.
  • High magnification.
  • Computer software programmes can add false colour to the image.
17
Q

Disadvantages of TEM.

A
  • 2D image.
  • Black and white (gray scale) image.
  • Only used on thin specimens.
  • Large microscopes.
  • Expensive.
  • Need lots of training and skills to be used.
  • Specimens have to be dead since viewed in a vacuum.
  • Metallic salt stains are potentially hazardous to the user.
18
Q

Disadvantages of SEM.

A
  • Image shows surface of specimen.
  • Large microscopes.
  • Expensive.
  • Need lots of training and skills to be used.
  • Specimens have to be dead since viewed in a vacuum.
19
Q

Magnification of

  • Optical microscopes
  • TEM
  • SEM
A

Optical microscopes = x1500
TEM = more than x1000,000
SEM = less than x500,000

20
Q

Resolution of

  • Optical microscopes
  • TEM
  • SEM
A

Optical microscopes = 0.2 um
TEM = 0.0002um
SEM = 0.002um

21
Q

Why staining is needed?

A

-If the specimen is transparent then the light just goes through rather than being absorbed so staining is used.

22
Q

Staining in optical microscopes.

A
  • Dye is used.
  • Common ones are Methylene Blue and Eosin.
  • Parts of specimen take up the stain more than others so the contrast makes the object show up.
23
Q

Differential staining.

A

Some stains bind to specific organelles/cell structures, staining each cell structure differently so the structures can be easily identified in a single preparation.
E.g. Eosin stains cytoplasm.

biology (13 decks)

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