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Biology > Microscope > Flashcards

Microscope Flashcards

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1
Q

Maginification

A

Size of image / size of real object

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2
Q

What are the two types of microscope

A

Transmission electron microscope and the scanning electron microscope

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3
Q

What is the resolving power of TEM

A

0.1nm

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4
Q

Why cant the resolving power always be reached when using a TEM

A

Difficulties preparing the specimen can limit the resolution that can be acheived

Higher energy electron beam is required and this could destroy the specimen

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5
Q

The electron gun in a transmission electron microscope produces…

A

A beam of electrons

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6
Q

The beam of electrons in a TEM is…

A

Focused onto the specimen by a condenser electromagnet

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7
Q

When using the TEM does the beam of electrons pass through the specimen or pass over it?

A

The beam of electron in a TEM passes through the specimen

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8
Q

Why do parts of specimen appear darker whenusing TEM

A

Parts of the specimen appear darker when observed throuhg TEM because the specimen absorb electron

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9
Q

Why do parts if specimen appear lighter when using TEM

A

Parts of the specimen appear lighter when observed through a TEM because the electrons pass through the specimen rather then the specimen absorbing it

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10
Q

Name three limitation of the transmission electron microscope

A
  1. Living specimen cannot be observed using the TEM because the whole microscope must be in a vacuum
  2. You have to carry out a complex staining process in order for the image to be seen (even then it is not in colour)
  3. The specimen used has to be extremely thin. The image may contain artefact which may lead to false result
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11
Q

How can we build a 3D image using a TEM

A

When using a TEM, the specimen has to be really thin to allow electrons to penetrate it therefore a 2d image is produced . To obtain a 3D image you would have to take a series of photomicrograph and then combine togther

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12
Q

What is a photomicrograph

A

A photograph of a microscope object, taken with the aid of a microscope

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13
Q

In which direction does the beam of electrons come from when using a TEM

A

The beam of electrons come from undermeath the specimen

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14
Q

In which direction does the beam of electron come from when using a SEM

A

The beamof electron come from above the specimen

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15
Q

Where is the beam of electron directed eithin a SEM

A

The beam is directed back and forth across a portion of the specimen on a regular pattern

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16
Q

TEM stands for..

A

Transmission electron microscope

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17
Q

SEM stands for…

A

Scanning electron microscope

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18
Q

What does the contouring of the specimen surface depend on

A

The contouring of a specimen surface depend on how the electron are scattered by the specimen

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19
Q

What is the resolving power of the SEM

A

20nm

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20
Q

How can a 3D image be produced of the specimen when using a SEM

A

A 3D image can be built on a computer when the pattern of the scattered electrons is analysed and secondary electrons are produced

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21
Q

How does a SEM work

A

A beam of electron is shone onto the surface of the specimen and they are reflected back onto a detector to produce the image

22
Q

What do light microscope use to make the object visible

A

Light rays

23
Q

What two things are better when using an EM compared to a light microscope

A
  1. Magnification

2. resolution

24
Q

What are the two types of lens used within a light microscope

A

Objective lens

Eyepiece lens

25
Q

Advantage of TEM

A

Really good magnification (5,000,000x)

This allows you to investigate specimens in greater depth

26
Q

Disadvantage of TEM

A

Have to have thinner layer of the specimen

Image are black and white

Expensive

Time consuming

27
Q

Advantage of SEM

A

Sample can be any thickness

Can be seen as a 3D image

28
Q

Disadvantage of SEM

A

Specimen must be conductive

Preparation of specimen can produce artefact

29
Q

Advantage of the light microscope

A
  • Can see living plants and animals or parts of them directly. This is useful and allows you to compare prepared slides with living tissue
  • relatively cheap so are available in schools and universities, hospitals, industrial lab and research labs
  • relatively light and portable so we can use them almost anywhere eg identifying malaria in the field
30
Q

Disadvantage of light microscope

A
  • Limited power of resolution (and magnification
  • preserving and staining tissue can produce artefacts. These artefact are not part of the living tissue. They are result of the process of preserving and staining, but it is easy to mistake them for part of the tissue
31
Q

Advantage of the electron microscope

A

-huge power of magnification and resolution. Many details of the cell structure have been seen for the first time using an electron microscope

32
Q

Disadvantage of the electron microscope

A
  • all specimen are examined in a vacuum-air would scatter the electrons and produce a blurred image of the tissue - so it is impossible to look at living material
  • extremely expensive
  • specimen undergo severe treatment that is likely to result in artefact. Preparing specimen for the electron microscope is very skilled work
  • the instrument is very large mist be kept at a constant temperature and pressure, and with an internal vacuum. Relatively few scientist outisde research labouratoried have easy access to this equipment
33
Q

Transmission electron micrograph measures

A

2D images

34
Q

Scanning electron micrograph

A

Lower magnification but 3D images

35
Q

Haematoxylin

A

Stains nuclei of plants and animal cells purple, blue or brown

36
Q

Methylene blue

A

Stains the nuclei of animal cells blue

37
Q

Acetocarmine

A

Stains the chromosome in dividing nuclei in both plant and animal cells

38
Q

Iodine

A

Stains starch-containing material in plant cells blue-black

39
Q

Magnification

A

Is the number of times larger an image appear compared with the size of the object

40
Q

Resolution

A

Is the ability to distinguish two points in an image

The higher the resolution the sharper the image

41
Q

Advantages of light microscope

A

Relatively cheap

Easy to use

Portable and able to used in field as well as fields

View in colour

View live specimens

42
Q

Disadvantages of micro

A

Low magnification (x1500)

Low resolution ( 200nm)

Difficult to see smaller organelles such as Golgi apparatus and ribosome

43
Q

What can be view by light microscope

A

The nucleus, cytoplasm, cell membrane, chloroplasts and cell wall are organelles which can be seen under a light microscope.

44
Q

TER

A

Can only be view dead specimen because specimen has to be dehydrated and stained with metal salts

Put under a vacuum

The electrons passes through the specimen

45
Q

TER advantages

A

High magnification (x2000000

High resolution ( 0.1nm

Look at smaller organelles such as ribosome and Golgi apparatus

46
Q

Disadvantages TER

A

Specimen can only be viewed in black and white

Specimen has to be dead

Only produce a 2D image of the cell

Larger and very expensive

Requires skill and training

47
Q

scanning electron microscope

A

Use electron to produce 3D images of the outside surface of the cell

Used to look at surface structure of the cell in more detail

The electron don’t pass through the specimen bounce off the surface of the specimen

Put under a vacuum

48
Q

Advantages of SER

A

High magnification x200000

High resolution x20nm

49
Q

SER disadvantages

A

Only view dead specimen

Larger and expensive

Require skills and training

50
Q

How to use a light microscope

A

The specimen on a slide is placed on the stage and use the clip to hold the slide

Use the lowest power objective lens

Adjust the course focus knob while looking through the eyepiece so that you can get a clearer image and so that it is in focus

Biology (27 decks)

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