Electron Microscopy. Flashcards
Define “resolution”:
The smallest distance between two points that can still be seen as two separate entities.
How do electron microscopes work?
• Electron microscopes use electrons instead of light to produce an image.
• Developed in the 1930s to allow scientists to see in greater detail than ever before.
• Greater resolution achieved by using high-energy electrons as the light source.
How do TEM microscopes work?
• Transmission Electron Microscopes (TEM) produce the most magnified images.
• They work 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.
How do SEM Microscopes work?
• Scanning Electron Microscopes (SEM) produce a three-dimensional image of a surface.
• They send a beam of electrons across the surface of a specimen.
• The reflected electrons are collected to produce an image.
Name 6 advantages and disadvantages about light microscopes:
• Cheap to buy and operate
• Small and portable
• Simple to prepare a sample
• Natural colour of sample is seen unless staining is used
• Specimens can be living or dead
• Resolution up to 0.2 um (2 × 10-7 m)
Name 6 advantages and disadvantages about electron microscopes:
• Expensive to buy and operate
• Large and difficult to move
• Sample preparation is complex
• Black and white images produced; false colour can be added to image
• Specimens are dead
• Resolution up to 0.1 nm (1 x 10-10 m)
What has the development of electron microscopy led to?
• Has allowed scientists to see the detail within subcellular structures, e.g.
chloroplasts.
• We now know, due to TEM microscopes, that chlorophyll is stored in flattened membranes within a chloroplast.
Name 4 parts of the Electron Microscope:
• electron source
• electron beam
• (specimen)
• electromagnetic lenses
• viewing screen
What is the formula for magnification.
Magnification = Image size/Actual Image.
M = I/A
(Mia!)
