Other types of microscopes

Description of light microscopes

-Compound microscopes are light illuminated

-The image seen with this type of microscope is 2D

-You can view individual cells, even living ones

What is the source of light microscopes?

visible light

what is the magnification of light microscopes?

x1500-2000

What is the resolution of light microscopes?

200nm

Description of scanning electron microscopes

-The image is seen in 3D

-The specimen is coated in gold and the electrons bounce off to give you an exterior view of the specimen

-The pictures are in black and white

-Specimens are dead as they have to be put in a vacuum

What is the source of scanning electron microscopes?

electrons

What is the medium of scanning electron microscopes?

vacuum

what is the magnification of scanning electron microscopes?

x100000

What is the resolution of scanning electron microscopes?

3-10nm

Description of transmission electron microscopes

-Image is seen as 2D

-Thin slices of specimens are obtained. The electron beams pass through this

-Specimens are dead as they have to be put in a vacuum

-A beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen

What is the source of transmission electron microscopes?

electrons

What is the medium of TEM?

x500000

what is the resolution of TEM?

0.5nm

Why are the specimens in electron in a vacuum?

To ensure that the electrons being fired are not interfered by the particles from the air

Why do electron microscopes have a higher resolution than light microscopes?

More detail of cell electron structure can be seen because electrons have a much smaller wavelength than light waves

They can produce images with magnifications of up to x500000 and still have a clear resolution

How are samples prepared for an electron microscope?

-It involves fixation using chemicals or freezing, staining with heavy metals and dehydration with solvents

-Samples for a TEM will then be set in resin and may be stained again

-Samples for a SEM may be fractured to expose the inside and will then need to be coated with heavy metals

Samples need to be prepared in this way because the inside of an electron microscope is a vacuum to ensure the electron beams travel in straight lines

what are artefacts?

A visible structural detail caused by processing the specimen and not a feature of the specimen e.g air bubbles

Why are samples dehydrated?

If there was water it would absorb the electrons

Why are samples stained with lead or uranium salts?

They are good at absorbing electrons. Therefore contrast can be increased because different structures absorb the materials differently

why are samples embedded in resin?

to prevent it from moving

What are the differences between SE and TE microscopes?

SE:

-Electrons reflect off the specimen

-Image is in 3D

-Lower resolution (3-10nm)

-Lower max magnification (100000)

-Internal cross section view

TE:

-Electrons go through the specimen

-Image is 2D

-Higher resolution (0.5nm)

-Higher max magnification (x500000)

-Surface view

Why are the images from electron microscopes in black and white?

the source is not visible light like it is in light microscopes, instead electrons are the source

What are false colour images?

using computer software to add colour

What are the advantages of light microscopes?

-Can view living organisms

-Easier to use

-Cheaper

-In colour

-Sample preparation does not often lead to distortion

-Portable

What are the disadvantages of light microscopes?

-Low magnification (up to x2000)

-Low resolution (200nm)

What are the advantages of SEM?

-Can see in 3D

-High magnification (x100000)

-High resolution (3-10nm)

What are the disadvantages of SEM?

-Cannot view living specimens

-More difficult to use

-Expensive

-Artefacts can be created from the processing of the specimen during preparation

-Not portable

-Sample preparation is complex

What are the advantages of TEM?

-High resolution (0.5nm)

-High magnification (x500000)

What are the disadvantages of TEM?

-Cannot view living specimens

-More difficult to use

-Expensive

-Artefacts can be created from the processing of specimen during preparation

-Not portable

-Sample preparation is complex

What are the lenses made of in light microscopes?

glass

What are the lenses made of in electron microscopes?

electromagnets

Why is fixation carried out?

maintains tissue in life like state

stops decomposition

How is fixation carried out on light microscopes?

uses chemicals such as methanal (formaldehyde)

How is fixation carried out for electron microscopes?

uses chemicals such as glutaraldehyde and osmium tetroxide

why is dehydration carried out?

removes water from tissue

how is dehydration carried out for a light microscope?

uses solvents such as ethanol

how is dehydration carried out for electron microscopes?

uses solvents such as ethanol