Microscopes and Microscopy Flashcards

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1
Q

What are the 3 types of microscopes?

A
  • optical microscopes
  • transmission electron microscopes
  • scnning electron microscopes
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2
Q

How do light (optical) microscopes work?

A

Relies on lenses to focus a beam of light

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3
Q

How do transmission electron microscopes work?

A
  • uses a beam of fast travelling electrons with a wavelength of 0.004nm fired from a cathode
  • the beam of electrons passes through the specimen
  • some pass through and are focused on the screen/ photographic plate
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4
Q

How do scanning electron microscopes work?

A

Electrons do NOT pass through the specimen, instead cause secondary electrons to ‘bounce off’ the specimen’s surface and be focused on the screen

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5
Q

Define photomicrograph

A

Photograph of the image seen using an optical microscope

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5
Q

Which type of microscope produces a photomicrograph?

A

An optical microscope

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6
Q

What are the benefits of using an optical microscope?

A
  • linear magnification
  • stains not required for coloured objects
  • can be used to study whole living organisms
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7
Q

What is a drawback of using an optical microscope?

A

It has a limited resolution

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8
Q

Define electron micrograph

A

Electrons form an image that a photograph is taken of

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9
Q

What microscopes produce electron micrographs?

A
  • scanning electron microscopes
  • transmission electron microscopes
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10
Q

Describe the type of electron micrograph produced by a transmission electron microscope

A
  • 2D
  • black and white image
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11
Q

State the benefits of a transmission electron microscope

A
  • high magnification achieved
  • 0.1 nm resolution
  • ultrastructure (internal structure) seen
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12
Q

State the drawbacks of a transmission electron microscope and a scanning electron microscope

hint: both have the same drawbacks

A
  • need skill and training to use
  • specimens have to be chemically fixed
  • speciment must be viewed under a vacuum
  • can’t study living things
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13
Q

Describe the type of image produced by a scanning electron microscope

A
  • 3D
  • black and white image
  • a computer can artificially add colour onto the image
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14
Q

State the benefits of a scanning electron microscope

A
  • whole specimen can be used
  • higher magnification and resolution
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15
Q

Define magnification

A

Describes how much larger an image appears when compared with the original object

16
Q

Define linear magnification

A

If a specimen is magnified x100, it appears to be x100 wider and x100 longer than it actually is

17
Q

Define resolution

A

The ability of an optical instrument to see or produce an image that shows fine details clearly

18
Q

What are the two different kinds of slides?

A
  • wet mount
  • stained slides
19
Q

Describe how to create a slide with a wet mount

A
  1. Place a drop of water on the slide
  2. Place your sample speciment in your drop of water
  3. Set a cover slip over the sample specimen at a 45 degree angle
20
Q

Describe how to create a stained slide

A
  1. Set a coverslip over the sample specimen at a 45 degree angle
  2. Place 1 drop stain on the other side of the cover slip
  3. The staining agent will begin to seep under the cover slip as the paper towel draws water out from the other side
21
Q

Define stain

A

Coloured chemicals that bind to other molecules in or on the specimen, making the specimen easy to see

22
Q

Define differential staining

A

Staining each subcellular structure differently so the structures are easily identifiable within a single preparation

23
Q

Describe how to prepare the specimens for electron microscopes

A
  1. Chemically fix the specimen
  2. Dehydrate it
  3. Embedd it in wax
  4. Use a special instrument to make very thin slices called sections
  5. stained and mounted in special metal salts
24
Q

Define graticules

A

Small disc with an engraved ruler
–> can be placed into the eyepiece of a microscope to act as the ruler in the field of view

25
Q

What are low power drawings?

A
  • better to use lower magnification lens
  • an outline of tissues
  • no individual tissues drawn
26
Q

What are high power drawings?

A
  • better to use high magnification lens
  • individual cells drawn
27
Q

State the magnification formula

A

magnification = image size/ actual size

28
Q

**

How many divisions does an eyepiece graticule have?

A

100

29
Q

What is the formula for eyepiece division length?

A

(no. of stage divisions x length of one stage division)/ no. of eyepiece divisions

30
Q

Explain how to calibrate an eyepiece graticule.

A
  1. Place a stage micrometer on the stage of the microscope.
  2. Line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.
  3. Count the number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer.
  4. Calculate the distance in micrometres of one division on the eyepiece graticule.