The Electron Microscope Flashcards Preview

Biology-3-Cell Structure > The Electron Microscope > Flashcards

Flashcards in The Electron Microscope Deck (11):
1

What are the two main advantages of an electron microscope

The electron beam has a very short wavelength and the microscope can therefore resolve objects well, it has a high resolving power

As electrons are negatively charged the beam can be focused using electromagnets

2

What are the 2 types of electron microscopes

Transmission Electron microscope

Scanning electron microscope

3

How does TEM work

It uses electromagnets to focus a beam of electrons which is then transmitted through the specimen. Denser parts of the specimen absorb more electrons, which make
s them look darker on the image you end up with

4

How does SEM work

Scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. Gives excellent 3D images

5

Which has a better resolution TEM OR SEM

TEM

6

What's the advantages and disadvantages of a light microscope

+ can be used to view live whole specimens under low magnifications

-low resolution does not allow much subcellular detailed to be observed

7

What's the advantages and disadvantages of TEM

+ uses beams of electrons
Short wavelength
High resolution so more detail

-electrons scattered
Must be in a vacuum therefore cannot examine living cells
Lots of preparation
May alter appearance
Very thin specimen
Black n White images

8

Advantages and disadvantages of SEM

+creates 3D effect of image of the surface of the specimen
Can be used on thick specimens

-specimen are always dead and may contain artefacts as a result of preparation techniques
Give lower resolution images

9

Explain how the electron microscope is able to resolve objects better then the light microscope

The EM uses a beam of electrons that has a much smaller wavelength then light

10

Explain why specimens have to be kept in a near vacuum in order to be viewed effectively using an electron microscope

Electrons Are absorbed by the molecules in air, and if present, this would prevent the electrons reaching the specimen

11

In practice, the theoretical resolving power of an electron microscope cannot always be achieved. Explain why not.

The preparation of the specimens may not be good enough. A higher energy electron beam is required and this many destroy the specimen