Cell Structure: Electron Microscopy

Question 1

What do electron microscopes use instead of light beams?

Answer 1

Electron beams

Question 2

Why are electrons used?

Answer 2

Electrons have a very short wavelength so the resolution of the image is 2000x better than a light microscope.

Question 3

Why do electrons have a wavelength?

Answer 3

Electrons have properties of both particles and waves.

Question 4

What are the key parts of a Transmission Electron Microscope and their functions?

Answer 4

Electron Gun-Where beam is fired from.
Electromagnetic lenses-Used to focus electron beam, as electrons have a negative charge.
In a Vacuum-so electrons can pass through without bouncing off molecules of air.
Specimen
Fluorescent Screen-Produce an image, from electron beam passing through the specimen.

Question 5

State the disadvantages of using a TEM.

Answer 5

-Produces 2D, flat images.
-Only works if the specimen is very thin.
-Live specimen cannot be used; due to vacuum conditions.
-Staining must be very careful and precise.
-Artefacts may be created during the staining process or the conditions inside the electron microscope.

Question 6

State the advantages of using a TEM.

Answer 6

-High resolving power , up to 0.1 nm
-Many discoveries have been made using these , such as the ribosomes or the structure of the cell membrane.
-Higher magnification so smaller parts can be visualised.

Question 7

What does TEM stand for?

Answer 7

Transmission Electron Miscroscope

Question 8

State the key parts of a Scanning Electron Microscope and their functions.

Answer 8

Electron Gun-Where beam is fired from.
Electromagnetic lenses-Used to focus electron beam, as electrons have a negative charge.
In a Vacuum-so electrons can pass through without bouncing off molecules of air.
Electron Detectors-to detect scattered electrons and then produce an image.
Specimen

Question 9

State the advantages of using a SEM.

Answer 9

-3D images.
-Does not require very thin specimen
-High resolution
-High magnification

Question 10

State the disadvantages of using a SEM.

Answer 10

-Cannot use live specimen
-Has a lower resolving power than the TEM
-Requires specimen to be coated in a metal, e.g. gold.
-Can produce artefacts due to the metal coating of specimen.

Question 11

How is an image created in the SEM?

Answer 11

Electron beam does not pass through the specimen, but hits it and the electrons scatter and are detected by electron detectors. These then form a 3D image.