Microscope Flashcards
Maginification
Size of image / size of real object
What are the two types of microscope
Transmission electron microscope and the scanning electron microscope
What is the resolving power of TEM
0.1nm
Why cant the resolving power always be reached when using a TEM
Difficulties preparing the specimen can limit the resolution that can be acheived
Higher energy electron beam is required and this could destroy the specimen
The electron gun in a transmission electron microscope produces…
A beam of electrons
The beam of electrons in a TEM is…
Focused onto the specimen by a condenser electromagnet
When using the TEM does the beam of electrons pass through the specimen or pass over it?
The beam of electron in a TEM passes through the specimen
Why do parts of specimen appear darker whenusing TEM
Parts of the specimen appear darker when observed throuhg TEM because the specimen absorb electron
Why do parts if specimen appear lighter when using TEM
Parts of the specimen appear lighter when observed through a TEM because the electrons pass through the specimen rather then the specimen absorbing it
Name three limitation of the transmission electron microscope
- Living specimen cannot be observed using the TEM because the whole microscope must be in a vacuum
- You have to carry out a complex staining process in order for the image to be seen (even then it is not in colour)
- The specimen used has to be extremely thin. The image may contain artefact which may lead to false result
How can we build a 3D image using a TEM
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
What is a photomicrograph
A photograph of a microscope object, taken with the aid of a microscope
In which direction does the beam of electrons come from when using a TEM
The beam of electrons come from undermeath the specimen
In which direction does the beam of electron come from when using a SEM
The beamof electron come from above the specimen
Where is the beam of electron directed eithin a SEM
The beam is directed back and forth across a portion of the specimen on a regular pattern
TEM stands for..
Transmission electron microscope
SEM stands for…
Scanning electron microscope
What does the contouring of the specimen surface depend on
The contouring of a specimen surface depend on how the electron are scattered by the specimen
What is the resolving power of the SEM
20nm
How can a 3D image be produced of the specimen when using a SEM
A 3D image can be built on a computer when the pattern of the scattered electrons is analysed and secondary electrons are produced
How does a SEM work
A beam of electron is shone onto the surface of the specimen and they are reflected back onto a detector to produce the image
What do light microscope use to make the object visible
Light rays
What two things are better when using an EM compared to a light microscope
- Magnification
2. resolution
What are the two types of lens used within a light microscope
Objective lens
Eyepiece lens
Advantage of TEM
Really good magnification (5,000,000x)
This allows you to investigate specimens in greater depth
Disadvantage of TEM
Have to have thinner layer of the specimen
Image are black and white
Expensive
Time consuming
Advantage of SEM
Sample can be any thickness
Can be seen as a 3D image
Disadvantage of SEM
Specimen must be conductive
Preparation of specimen can produce artefact
Advantage of the light microscope
- 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
Disadvantage of light microscope
- 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
Advantage of the electron microscope
-huge power of magnification and resolution. Many details of the cell structure have been seen for the first time using an electron microscope
Disadvantage of the electron microscope
- 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
Transmission electron micrograph measures
2D images
Scanning electron micrograph
Lower magnification but 3D images
Haematoxylin
Stains nuclei of plants and animal cells purple, blue or brown
Methylene blue
Stains the nuclei of animal cells blue
Acetocarmine
Stains the chromosome in dividing nuclei in both plant and animal cells
Iodine
Stains starch-containing material in plant cells blue-black
Magnification
Is the number of times larger an image appear compared with the size of the object
Resolution
Is the ability to distinguish two points in an image
The higher the resolution the sharper the image
Advantages of light microscope
Relatively cheap
Easy to use
Portable and able to used in field as well as fields
View in colour
View live specimens
Disadvantages of micro
Low magnification (x1500)
Low resolution ( 200nm)
Difficult to see smaller organelles such as Golgi apparatus and ribosome
What can be view by light microscope
The nucleus, cytoplasm, cell membrane, chloroplasts and cell wall are organelles which can be seen under a light microscope.
TER
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
TER advantages
High magnification (x2000000
High resolution ( 0.1nm
Look at smaller organelles such as ribosome and Golgi apparatus
Disadvantages TER
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
scanning electron microscope
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
Advantages of SER
High magnification x200000
High resolution x20nm
SER disadvantages
Only view dead specimen
Larger and expensive
Require skills and training
How to use a light microscope
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
