B1.1.4 Electron Micrscopy

Question 1

What is the definition of resolution

Answer 1

The smallest distance between two points that can be seen as separate entities

Question 2

What is magnification?

Answer 2

How many times bigger the image of a specimen observed is in compared to the actual size of the specimen.

Question 3

What is the smallest measurement you can see a structure with a light microscope?

Answer 3

0.2 micrometers (2x10^-7m)

Question 4

What are some advantages of using a light microscope instead of TEM?

Answer 4

• cheaper
• portable
• sample can be alive
• sample easy to prepare
• natural colours seen

Question 5

What do electron microscopes use instead of light to produce an image

Answer 5

High energy electrons

Question 6

What are the two types of electron microscopes?

Answer 6

Transmission electron microscopes
Scanning electron microscopes

Question 7

How do TEM work

Answer 7

in a similar way to a light microscope.
A beam of electrons passes through a very thin slice of the sample.
The beam is focused to produce an image

Question 8

How do SEM work

Answer 8

produce a three-dimensional image of a surface
send a beam of electrons across the surface of a specimen
the reflected electrons are collected to produce an image

Question 9

Compare TEM and SEM microscopes

Answer 9

Advantage: TEM create the most magnified image
Disadvantage: SEM creates a 3D image of the specimen, whereas TEM only magnifies a certain area of the sample

Question 10

Advantages of light microscope over electron

Answer 10

Cheaper to buy and operate whereas electron microscopes are expensive to buy and operate
Small and portable whereas electron microscopes are large and difficult to move
Simple to prepare a sample whereas sample preparation for electron micro are complex
Natural colour of the sample is seen unless stained whereas electron microscopes produce black and white images so false colour could be added to them
Specimens can be living or dead whereas specimens must be dead for an electron microscope

Question 11

Why did scientists not know what viruses looked like before the 1930s? (3)

Answer 11

Since they used light microscopes which only have a resolution up to 0.2um, viruses are far smaller than that.
The electron microscope was introduced in 1931, having a resolution of 0.0001 um, allowing viruses to be seen

Question 12

Why can’t a light microscope be used to see inside a sub cellular structure?

Answer 12

It has low magnification and resolution (x 1,500 -> 2000 and 200nm respectively ), so sub-cellular structures cannot be easily seen