Module 2: More microscopy

Question 1

Describe how an electron microscope is used ( 1 point )

What does this allow in terms of what can be seen ?

Answer 1

• a beam of electrons with a wavelength less than 1 nanometre is used to illuminate the specimen

this allows more detail of cell ultrastructure to be seen

Question 2

State 5 disadvantages of electron microscopes …

Answer 2

-they are very expensive
-they can only be used in carefully controlled environments
-specimens can be damaged by the beams
-there is a problem of artefacts
-they only produce black and white images

Question 3

Name the 2 different types of electron microscope

Answer 3

Transmission electron microscope
Scanning electron microscope

Question 4

Describe how both the types of electron microscopes work …

3 points for each , including their resolving powers

Answer 4

TEM:
-a beam is transmitted through the specimen and focused to produce an image
-has the best resolution with a resolving power of 0.5nm
-produces 2D images

SEM:
-beam is sent across the surface of the specimen and reflected electrons are collected
-has a resolving power of 3-10nm
-produces 3D images so gives valuable info about appearance of organisms

Question 5

The inside of electron microscopes are a …
Why?

So this means that specimens are …

Answer 5

vacuum, to ensure beams travel in a straight line

not alive

Question 6

What is an artefact?

Answer 6

a visible structural detail caused by the processing of the specimen