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

Optical and Electron Microscopy

Extracts from this document...


Biology essay:

Optical and Electron Microscopy:


   Microscopes allow us to see things so small they normally can’t be seen by the naked eye. The intention of all microscopic studies is to produce an image that is a copy of the object, or the specimen.

   There are two main aspects to a microscope, which determine the image - magnification and resolution. The magnification is the number of times the image is linearly larger than the object. So, small objects will appear larger in the image under higher magnification than under lower magnification. The resolution, or resolving power, is the microscope’s ability to differentiate between small objects that are close together. Theoretically the electron microscope has 100,000 x better resolving power than optical microscopes, but in practise the resolution of an electron microscope is at best 1 nm (nanometre), i.e. two objects less than 1 nm apart will be seen as one.  

Optical Microscopy:

   The main instrument, which utilizes light to produce a magnified image, is the compound microscope. A compound microscope uses the magnifying power of two convex lenses, the eyepiece and the objective lens, which itself has three variable magnifying powers – low, medium and high, to produce an image.

...read more.


embedding, would not mix if any water were present. Dehydration is usually accomplished by gradually increasing the concentration of added alcohol, usually ethanol, until ‘absolute alcohol’ is reached – nearly pure alcohol.

3. Clearing:

   In most cases alcohol is immiscible with the embedding, see next stage, or mounting media, so it is replaced by a clearing agent, such as xylol or xylene, which does mix. The agent also makes the material transparent, which is necessary, as light rays must travel through the specimen into the eye.

4. Embedding:

   Before the material can be cut into thin sections to allow light through, it must be embedded using a supporting medium so that the slices do not collapse. In optical microscopy, the material is impregnated with molten wax, which consequently sets.

Biology Essay Continued:

5. Sectioning:

   Once the wax has settled, the material can be cut up into thin sections. This is either done using a razor or a microtome. The latter being a machine that cuts extremely thin slices, usually between 3 and 20 micrometres. A freezing microtome may be used which avoids the need of embedding as the specimen is frozen and therefore firm. A razor can

...read more.


Scanning Electron Microscopy: (SEM)

   In SEM the whole specimen is exposed to a beam of electrons. An image is then created from the electrons reflected from the surface of the object. Although the resolution isn’t as good as with TEM, scanning electronmicrographs show depth of focus and the object is three-dimensional. Another advantage is that SEM allows larger specimens to be examined.

   When comparing optical microscopy and electron microscopy, it is clear that each has its own advantages and disadvantages over the other. Obviously, an electron microscope produces an image of greater magnification and resolution than optical microscopes due to the very nature of light, but electron microscopy doesn’t produce coloured images. EM is also very expensive and preparation takes a lot of time. Another disadvantage in EM is that the specimen has to be nonliving, which can be a cause for irritation as studying living material under high magnification and resolution would help us to learn more about cell structure and function, for example.

   To conclude, the choice of one type of microscopy over the other is dependant on the requirements of the given study. For example, if one wanted to observe the structure of mitochondria one would choose EM over optical microscopy because it has greater magnification and resolving powers.  

...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. Peer reviewed

    The advantages and limitations of electron microscopy.

    4 star(s)

    This presents problems when preparing specimens as: * All specimens have to be dead as nothing can survive in a vacuum. * All specimens must be fully dehydrated as water boils at room temperatures in a vacuum. * All specimens must be encased in resin-type substances, as there is no

  2. To investigate the relationship between the distance between a lens and an object, and ...

    and display the results on a computer. The experiment is also subject to the condition of the lens. Although the lens is supposed to have a 10cm focal point, poor grinding or damage subsequent to its production may change this by a small amount.

  1. In this experiment I will be investigating the efficiency of a motor. I hope ...

    Object Distance/ u (cm) [1/u] Image Distance/ v (cm) [1/v] Focal Length (cm) 1/f = 1/u + 1/v 1 (...) Average: 2 (...) Average: 1&2 Combined (...) Average: Sensitivity: In this experiment it is important that I am aware of errors; I can decrease the amount of inaccuracies by checking

  2. Advantage and disadvantage of using an optical and electron microscope.

    The specimen has to be cut very thin, so usually it is no more than 500nm thick. A fluorescent screen is placed under it so it can sample the magnified image.

  1. Relationship Between U and V For a Convex Lens

    Graphs Analysis I have proven that as u increases v decreases. This happens because as v increases (the object distance), it means the middle rays of light from the top of the image changes. It changes so that as u increases, the middle ray goes through the principal axis and convex lens at a much smaller angle.

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

    I believe they are scattered due to the fact that the higher 'U' values lead to higher uncertainties in 1/V. This means the graph cannot be entirely reliable. Considering these factors I would say that my results are generally reliable taking into account that it is the first experiment.

  1. An investigation into the workings of the opticians

    in front of the macula so when the light hits the macula it is slightly dispersed. This problem means that sufferers can focus on objects that are nearby clearly but distant objects appear blurred. Hyperopia Also known as 'far' or 'long' sightedness this occurs when the light focused by the

  2. This essay is on vision, its malfunctions & diagnostics methods.

    Subjective methods include the Snellen Chart Test, in which the optotype is placed twenty feet (6 meters) away from the subject. Some individuals may well wear spectacles in which case the examination is performed with the subject wearing them. The eye which is adversely impaired out of the two is examined first.

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