Ch. 2.3: More Microscopy

Question 1

How do electron microscopes work generally?

Answer 1

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

Question 2

Why are electron microscopes better ( generally ) than light microscopes?

Answer 2

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

Question 3

How do transmission electron microscopes work? Resolution?

Answer 3

A beam of electrons is transmitted through a specimen and focused to produce an image. This has the best resolution with a resolving power of 0.5 nm

Question 4

How do scanning electron microscopes work? Resolution ?

Answer 4

A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected. The resolving power is from 3-10nm, so it’s not as good as a TEM but three dimensional images of surfaces are produced which is valuable.

Question 5

What are the advantages of light microscopes?

Answer 5

• inexpensive to buy and operate
• small and portable
• simple sample preparation
• sample preparation does not usually lead to distortion
• vacuum is not required
• natural colour of sample is seen ( or stains are used)
• specimens can be living or dead
• image can be viewed directly

Question 6

What are the disadvantages of light microscopes?

Answer 6

• relatively low magnification ( up to x2000)

- relatively low resolution ( 200nm)

Question 7

What are the advantages of transmission electron microscopes?

Answer 7

• high magnification and resolution produces detailed images of cells and organelles
• allows internal structures of cells/ organelles to be seen

Question 8

What are the advantages of scanning electron microscopes?

Answer 8

• produces 3D images

- reveals details of contours and cell / tissue arrangements

Question 9

What are the disadvantages of electron microscopes generally?

Answer 9

• Expensive to buy and operate
• large and needs to be installed
• complex sample preparation
• sample preparation often distorts material
• vacuum is required
• black and white images produced
• specimens have to be dead

Question 10

What are the advantages of electron microscopes generally ?

Answer 10

• over x500 000 magnification

- resolving power is high : TEM - 0.5 nm SEM - 3–10 nm

Question 11

What are the limitations of scanning electron microscopes?

Answer 11

• requires expensive and difficult staining
• only reveals the surface detail from a specimen
• images can’t be viewed directly

Question 12

What are the limitations of transmission electron microscopes ?

Answer 12

• produces 2D images of thin cross sections of a specimen

- images can’t be viewed directly

Question 13

How does a laser scanning confocal microscope work?

Answer 13

• it moves a single spot of focused light across a specimen ( point illumination )
• this causes fluorescence from the components lab elder with a dye
• the emitted light from a specimen is filtered through a pinhole aperture. Only light radiated from very close to the focal plane is detected
• unwanted light emitted from other parts does not pass through the pinhole and is not detected.
• therefore it has a very high resolution

Question 14

What are the advantages of laser scanning confocal microscopy?

Answer 14

• non evasive eg see back of the eye in optometry

- high resolution as there is limited blurring as they only see one layer of the specimen