The Electron Microscope - 3.2 Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What are the two main advantages of an electron microscope?

A
  • The electron beam has a very short wavelength and the microscope can therefore resolve objects well - it has a high resolving power.
  • As electrons are negatively charged, the beam can be focused using electromagnets.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the two types of electron microscope?

A
  • The transmission electron microscope (TEM)

- The scanning electron microscope (SEM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the TEM consist of?

A

An election gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does the TEM work?

A

In a TEM, the beam passes through a thin section of the specimen. Parts of this specimen absorb electrons and therefore appear dark. Other parts of the specimen allow the electrons to pass through and so appear bright. An image is produced on a screen and this can then be photographed to give a photomicrograph.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the resolving power of the TEM?

A

0.1 nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why can the resolving power of the TEM not always be achieved?

A
  • Difficulties preparing the specimen limit the resolution that can be achieved.
  • A higher energy electron beam is required and this may destroy the specimen.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the main limitations of the TEM?

A
  • The whole system must be in a vacuum and therefore living specimens cannot be observed.
  • A complex ‘staining’ process is required and even then the image is not in colour.
  • The specimen must be extremely thin.
  • The image may contain artefacts. Artefacts are things that result from the way the specimen is prepared. Artefacts may appear on the finished photomicrograph but are not part of the natural specimen. It is therefore not always easy to be sure that what we see on a photomicrograph really exists in that form.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

In the TEM, the specimen must be extremely thin to allow electrons to penetrate, what does this result in?

A

A flat, 2D image.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How can we overcome the fact that the TEM only produces a 2D image?

A

We can partly get over this by taking a series of sections through a specimen. We can then build up a 3D image of the specimen by looking at the series of photomicrographs produced. However, this is a slow and complicated process.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the benefits of the SEM over the TEM?

A

-Specimens don’t need to be extremely thin as electrons do not penetrate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How does the SEM work?

A

The SEM directs a beam of electrons onto the surface of the specimen from above, rather Tham penetrating it from below. The beam is then passed back and forth across a portion of the specimen in a regular pattern. The electrons are scattered by the specimen and the pattern of this scattering depends on the contours of the specimen surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does the SEM produce?

A

A 3D image, produced by computer analysis of the pattern off scattered electrons and secondary electrons produced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why is the SEM less useful than the TEM?

A

The basic SEM has a lower resolving power than a TEM, around 20nm, but is still ten times better than a light microscope.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the resolving power of the SEM?

A

Around 20nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is resolution?

A

The smallest separation at which two separate objects/points can be distinguished.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the resolution limited by?

A

The wavelength of light used.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How does a light microscope work?

A

Uses a series of lenses to produce an image that can be viewed directly at the eyepiece. Light passes from a bulb under the stage, through a condenser lense and then through the specimen. This beam of light is passed through an objective and then eyepiece lense

18
Q

Do light microscopes have high or low resolution?

A

Low

19
Q

What is the maximum resolution of s light microscope?

A

200nm

20
Q

What is the maximum magnification of a light microscope?

A

x1500

21
Q

What are the advantages of light microscopes?

A
  • Cheap
  • Portable
  • You can stain the sample
  • Able to study living material
22
Q

What are the disadvantages of light microscopes?

A
  • Low resolution

- Small cell organelle are not visible

23
Q

What is the staining technique?

A

Coloured stains bind to chemicals on or in the specimen allowing the specimen to be seen, due to increased contrast

24
Q

What is magnification?

A

How much bigger the image is compared to the original object

25
Q

What is sectioning?

A
  • Specimens are embedded in wax- thin sections are cut out without distorting the specimen
26
Q

What is sectioning useful for?

A

Making slides/sections of soft tissues such as brain

27
Q

What is a TEM?

A

Transmission electron microscope

28
Q

How does a TEM work?

A

Transmit a beam of electrons through a thin specimen and then focus the electrons to form an onscreen image

29
Q

What are the advantages of TEMs?

A
  • Highly detailed images of cells and organelles

- High resolution

30
Q

What are some disadvantages or TEMs?

A
  • Can’t study living material due to extensive preparation and vacuum
  • Expensive
  • Specific skill and training for sample preparation
31
Q

What is the maximum resolution of a TEM?

A

0.1 nm

32
Q

What is the maximum magnification of a TEM?

A

x500000

33
Q

What is a SEM?

A

Scanning electron microscope

34
Q

How does an SEM work?

A

By scanning a fine beam of electrons onto a specimen and collecting the electrons scattered by the surface

35
Q

What are advantages of SEMs?

A
  • 3D images of cell surface
  • Detailed
  • Powerful magnification
36
Q

What are some disadvantages of SEMs?

A
  • Can’t see inside cells
  • Expensive
  • Can’t study living organisms
  • Specific training for sample preparation
37
Q

What is the maximum magnification of an SEM?

A

x100000

38
Q

What is the maximum resolution of an SEM?

A

2nm

39
Q

What is the formula for calculating magnification?

A

Magnification= image size ➗ actual size

40
Q

What stain (chemical ) is used for staining plant cells?

A

Iodine

41
Q

What stain is commonly used for staining animal cells?

A

Methylene blue