3.6.2 Scanning and Transmission Electron Microscopes

Question 1

review

Answer 1

• Compound, or light microscopes, are limited due to the resolving power of visible light. Illuminating a specimen with a smaller wavelength would solve the problem of resolution.

Question 2

Scanning and transmission electron microscopes

Answer 2

• use electrons instead of visible light to illuminate a specimen. Electrons have a much shorter wavelength and enable greater resolution at higher magnification than is possible in a compound microscope.

Question 3

electron microscopes

Answer 3

• use a beam of electrons instead of light for generating an image of a specimen. Instead of lenses, electron microscopes use electromagnets to bend the electron beam and magnify and focus the image onto a screen. The result is a resolving power that is increased to allow magnification of up to 1,000,000 times versus a 1,000 times, as in the compound microscope.

Question 4

transmission electron microscope (TEM)

Answer 4

• A specimen is cut into extremely thin slices, and an electron beam is directed through the specimen. The resulting picture reveals detail about the internal structure of a specimen.

Question 5

scanning electron microscope (SEM)

Answer 5

• An electron beam scans the surface of an object that has been coated in metal. When the beam hits the metal, the metal emits electrons. The electrons are focused to form an image. SEM images enable a magnified view of surface details.

Question 6

Pictures taken by a scanning electron microscope can be viewed by

Answer 6

• a fluorescent screen

Question 7

Light microscopes can magnify up to __________ times the original size with good resolution but electron microscopes can magnify __________ times with good resolution.

Answer 7

• 1,000; 1,000,000

Question 8

How do the images generated by a transmission electron microscope and a scanning electron microscope differ?

Answer 8

• A transmission electron microscope passes a beam of electrons directly through a specimen.

Question 9

As a graduate student, you are required to take detailed pictures of the progressive stages of DNA coiling. You should probably use a

Answer 9

• transmission electron microscope because of its resolving power.

Question 10

If you would like to examine the surface features of a ribosome, you should probably use a

Answer 10

• scanning electron microscope