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Electron microscopes.

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This is the act of using electron microscopes. Electron Microscopes are scientific instruments that use a beam of highly energetic electrons to examine objects on a very fine scale. Electron microscopes can be used to view the topography (surface), the morphology (the shape and size of the particles making up the object) and also the composition (elements and compounds the object is composed of and how many: in case of cell organelles).

Electron microscopes were introduced or developed due to the limitation of light microscopes. This is because the resolving power of a microscope depends on the wavelength of the electromagnetic radiation used; because the light microscope uses only the visible part (light) of the electromagnetic spectrum whose shortest wavelength is 400 nanometre (violet light), therefore objects smaller than half of the wavelength (200nm) cannot be viewed using a light microscope. E.g. cell organelle ribosome is 20nm and can never be seen using a light microscope. As electron microscopes uses electrons, which are negatively charged and beams of electrons have a very short wavelength.

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 are seen. This microscope allows us to see as separate structures, particles which are as close together as 2 nanometres, thus the resolution of this microscope is about 2 nanometres. Because of its high-resolution power the electron microscope can be used at low as well as high magnification.

The other type of electron microscope is the scanning electron microscope. In this type the electron beams is used to scan the surfaces of the structures and only the beams reflected by the surface is viewed. The scanning electron microscope gives a three-dimensional effect showing surface detail. Though both of these electronic microscopes are very effective, the scanning electron microscope can take longer specimens that the transmission electron microscope can. On the other hand the scanning electron microscope does not have such a high resolving power as the transmission electron microscope does.

Photographs of specimen viewed by electron microscope called electronmicrographs, Before any electronmicrographs can be viewed the specimen which is to be viewed has be prepared. These specimens need to be cut appropriately and stained.

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Even though the electron microscope is very effective and has very high magnification and resolution power, it also has some problems. For example the specimen, the electron beam and the fluorescent screen must all be in a vacuum. This is because if the electron beams being used collide with air molecules they will scatter making it impossible to achieve a sharp picture. Also because water boils at room temperature in a vacuum the entire specimen must be dehydrated before being placed in the microscope. This means only dead specimen can be viewed, which is a great fall back to the electron microscope. Lastly unlike the light microscope the images produced are not coloured. They are either in shades of black or white. As at now many researchers are being carried out to be able to see living cells under these powerful microscopes.

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Response to the question

The candidate gives a detailed response, they clearly describe how electron microscopes are used and outline the advantages in comparison to an optic microscope. In addition to this the candidate has written a suitable introduction and states the uses of ...

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Response to the question

The candidate gives a detailed response, they clearly describe how electron microscopes are used and outline the advantages in comparison to an optic microscope. In addition to this the candidate has written a suitable introduction and states the uses of microscopes. This could be improved further my stating what they planned to discuss. It is sometimes useful to write your introduction last so that you introduce the topics you discuss.

Level of analysis

The candidate shows a good understanding of how electron microscopes work, they have provided a suitable level of detail and have stated the advantages and disadvantages of using this type of microscope. In addition to this the candidate has shown knowledge beyond that expected for this level of qualification as they have provided details of how specimens are prepared. This additional information is interesting for the reader and shows the candidates enthusiasm for their subject. Unfortunately the candidate has not written a conclusion, which is a mistake. A conclusion is essential to any type of essay, it gives you a chance to summarise your key points and allows you to draw the essay to close, leaving the reader with a good impression.

Quality of writing

There are a few issues with spelling and a few incoherent sentences. This is easy to avoid if you proof read your work and make sure you use a spell check. Overall the essay is reasonably well written and shows a good level of understanding.

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Reviewed by pictureperfect 30/06/2012

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