• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Electron Microscopy.

Extracts from this document...


Electron Microscopy

An electron microscope can only show dead structures, but will show cell ultrastructure including the fine structure of the cell organelles. When using an electron microscope, the specimen is illuminated in an electron microscope by an electron beam. The electron beam is focused using electromagnets arranged around the path of the electron beam. These electrons then produce an image when focused onto a fluorescent screen. This image is formed from electrons, which have been emitted or reflected from the surface of a complete specimen.

There are two different types of electron microscopes: a transmission electron microscope and a scanning electron microscope. The electrons pass through or past a thin section of the specimen in a TEM on their way to the fluorescent screen or photographic film. In SEMs the electrons are reflected off the prepared surface of the specimen.

...read more.


The scanning electron microscope gives a three-dimensional effect, which shows surface detail. It scans electron beams to and fro across the surface of a complete specimen. It doesn’t have a resolving power as high as the transmission electron microscope. Despite this, it can take larger specimens than the transmission electron microscope.

The specimen for both electron microscopes must be very thin. This is because electrons must be able to pass through parts of the specimen. Molecules in air interrupt the flow of electrons. For this reason, the specimen is placed into a vacuum chamber, which is inside an electron microscope, before it is split along a line of weakness. Very small specimens such as viruses and large molecules do not have to be sectioned.

Photographs of specimens viewed with an electron microscope are called electronmicrographs.

...read more.


When using a scanning electron microscope, the process is different. First the tissue is frozen rapidly in liquid nitrogen at about –210°c. This technique is known as freeze fracture, which allows surface detail to be seen with a transmission electron microscope. The frozen tissue is then fractured into very thin sections with a sharp blade, made either of metal or glass. The ice is evaporated from the surfaced and the exposed surface is sputter coated with carbon or gold. Then carbon or a gold replica is floated off the tissue and finally it is mounted on a disc. The treatment might introduce artefacts.

The electron microscope is a useful tool to look at the ultrastructure of the cells, including the fine structure of the cell organelles. This is because of its ability to magnify specimens up to 500, 000 times.

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Microscopes & Lenses section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Microscopes & Lenses essays

  1. Optical and Electron Microscopy

    The stage micrometer value is then divided by the number of eyepiece units to give the length of one eyepiece unit in millimetres. The same is then done under medium and high power, using a 1 mm stage micrometer divided into hundredths of a millimetre, so that a value for

  2. History of the Microscope

    Place one drop of water directly over the specimen. If you put too much water over the specimen, then the cover slip will float on top of the water, making it harder to view the specimens as they float past the field of view. 4) Place the cover slip at a 45-degree angle (approximately), with one edge touching the water drop, and let go.

  1. My experiments focus is to obtain an accurate measurement for a specific lenss power.

    V Mean (x10-3 M) V +/- (x10-3 M) %V +/- 1/V Min. (D) 1/V Max. (D) 1/V Mean (D) 1/V +/- (D) 425 -2.35 238 246 242 4 1.65 4.21 4.07 4.14 0.0683 400 -2.5 243 251 247 4 1.62 4.12 3.98 4.05 0.0656 375 -2.67 251 259 255 4 1.571 3.98 3.86 3.92 0.0615 350 -2.86 265

  2. Electron Microscopy and the study of the Cell.

    When staining a sample it is embedded in a resin which becomes hard, when hard it is sliced into very thin pieces with a glass knife known as a microtome, it is then treated with a solution of a heavy metal salt like uranyl acetate, and then dehydrated.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work