1.5 Electron microscopy

Question 1

Define resolution

Answer 1

The ability to distinguish between two separate points

Question 2

If two points cannot be resolved

Answer 2

then they will be seen as one point

Question 3

The images with a higher resolution are more

Answer 3

clear and detailed

Question 4

The maximum resoution of a light microscope is

Answer 4

200 nm

Question 5

A resolution of 200nm means

Answer 5

that if two points are closer than 200nm then they cant be distinguished as separate

Question 6

One of the properties of light is that

Answer 6

It travels in waves

Question 7

The lengths of the waves of visible light vary from

Answer 7

400nm to 700nm

Question 8

How can the human eye see the light waves as colors

Answer 8

The human eye can distinguish between these differences and in the brain, the differences are converted into color differences.

Question 10

What is the electromagnetic spectrum?

Answer 10

The range of different wavelengths of electromagnetic radiation

Question 10

Visible light is a form of

Answer 10

electromagnetic radiation

Question 11

Waves that are 400 nm are seen as

Answer 11

Violet

Question 12

Waves that 700 nm in length are seen as

Answer 12

red

Question 13

The greater the energy of the wave

Answer 13

the shorter the wavelength

Question 13

The longer the waves

Answer 13

Thelower their frequency

Question 14

Why can a mitochondrion be seen using a light microscope but not s ribosome

Answer 14

The mitochondrion is large enough to interfere with the light waves. However, the ribosome are far too small to have any effect on the light waves.

Question 15

The general rule when viewing specimens is that the limit of resolution

Answer 15

is about one half of the wavelength the wavelength of the radiation used to view the specimen.

Question 16

If an object is smaller than half the wavelength of the radiation used to view the specimen

Answer 16

then it cannot be seen separately from nearby objects

Question 17

Why can a transparent object not be seen using light microscope

Answer 17

It will allow light waves to pass through itself and therefore still not be visible

Question 18

Why are electrons a suitable form of radiation to look at things smaller than 200nm

Answer 18

They have extremely short wavelengths
They are negatively charged so they can be focused easily using electromagnets

Question 19

Why do electrons have such short frequency

Answer 19

because they have great amounts of energy (especially after being heated)

Question 20

When do the electrons behave like an electromagnetic radiation?

Answer 20

When a metal becomes very hot, some of its electrons gain so much energy and escape from their orbits. Free electrons behave like electromagnetic radiation.

Question 21

Explain the importance of electromagnets in an electron microscope

Answer 21

A magnet can be used to alter the path of the beam, equivalent of a glass lens bending light.

Question 22

What is the resolution obtained using electron microscope?

Answer 22

0.5 nm

Question 23

What are the two types of electron microscope in use?

Answer 23

Transmission electron microscope(TEM) Scanning electron microscope(SEM)

Question 24

What type of electron microscope was the one originally developed?

Answer 24

Transmission electron microscope

Question 25

How does TEM work

Answer 25

The beam of electrons is passed through the specimen before being viewed. Only the electrons that are transmitted (pass through the specimen) are seen. This allows us to see thin sections of the cells and thus see inside them.

Question 26

How does SEM work?

Answer 26

The electron beam is used to scan the surfaces of structure. They hit the structure and only the reflected veam is observed.

Question 27

What is an advantage of SEM

Answer 27

The surface structures can be seen

Question 28

What is a disadvantage of SEM

Answer 28

It cannot give the same resolution as TEM. Using a SEM, a resolution between 3nm and 20nm is obtained.

Question 29

It is not possible to see an electron beam. How is this problem solved?

Answer 29

The electron beam has to be projected into fluorescent screen. The areas hit by electrons shine brightly giving an overall black and white image.

Question 30

The stains used to improve the contrast of biological molecules in electron microscopy contain

Answer 30

heavy metal atoms, which stop the passage of electrons.

Question 31

What are false-color images?

Answer 31

These are images that form when the standard black and white images formed using an electron microscope by using a computer.

Question 32

Why should the electron beam as well as the specimen and the fluorescent screen be in a vacuum?

Answer 32

If the electrons collided with air molecules, they would scatter making it impossible to achieve a sharp picture.

Question 33

Why must all specimens be dehydrated before being placed in the microscope

Answer 33

Water boils at room temperature in a vacuum.

Question 34

Why can only dead materials be examined using electron microscope?

Answer 34

It is because all specimens must be dehydrated before being placed in the electron microscope. However, great efforts are made to try to preserve material in a life like state.