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Describe the principles and limitations of transmission and scanning electron microscopes. Specific reference should be made to magnification and resolution

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Describe the principles and limitations of transmission and scanning electron microscopes.Specific reference should be made to magnification and resolution Introduction Microscopy has a major role in cytology.From the very beginning researchers have tried to develop ways of looking directly at living cells.This examination has revealed much about the morphology of cells and tissues.In recent years,development in microscopes,dyes,staining and preparatory techniques have helped reveal even more about the structure and function of cells.Microscopes have a certain magnification and resolving power.In any microscope the the resolving power is more important than the magnification.The resolving power of a microscope is the least distance between two objects where the microscope can still distinguish the objects as being separate.It is a measure of detail that can be seen.A microscope with a high resolving power enables us to view images with a high resolution.With a low resolution they would be viewed as one object.Microscopes with a high magnification are only able to increase the size of the object that is being viewed.The resolution will be the same.(ie the object will still lack clarity and appear fuzzy).The two types of microscopes are electron and light microscopes. ...read more.


Principles and Limitations of electron microscopy The other type of microscope is the electron microscope (which consists of transmission electron microscope and scanning electron microscope).It works by focussing a beam of electrons at the specimen.The electrons have a higher wavelength than photons of light hence the resolving power is greater.The beam of electrons are produced by a heated filament ,focussed on the specimen by the condenser lens and the image then magnified by the objective and projector lenses.The beam can be bent and focussed by electromagnetic lenses,in the same way the glass lenses are used in a light microscope.Unlike light microscopes ,the electron microscopes,have a high resolution(0.1 nm) and high magnification(1000000X) .The image formed by the electron microscope is projected onto a cathode ray tube so that it is visible to the operator ,looking rather like a black and white TV screen. The second type is the scanning electron microscope.They examine the surface of specimens.The surface is coated with a film of gold and palladium.A fine beam of electrons is passed backwards and forwards over the specimen.and the electrons that are reflected from it are collected and amplified to form an image on a cathode ray tube.Although the scanning electron microscope gives a much lower resolution(5-20nm) ...read more.


Conclusion Electron microscopes have been far more successful in determining cell ultrastructure compared to light microscopes.The high magnification and high resolution enables us to see cells and organelles much bigger and in much more detail.It has brought about the complete reappraisal of the microanatomy of biological tissues,organisms and cells.In early days of it's applications to biological materials,it was a tool of anatomists and histologists.The detailed knowledge of internal organisation of organelles has helped in our understanding of how they work.The fact that electron micrographs appear in many research papers and books in cell biology and anatomy emphasize the importance of electron microscopy to the biologists not only in the present times but also in future.Today electron microscopy is widely used in metallurgy,biology,material science,physics,chemistry and many other biological fields.It has been an integral part in the understanding of the complexities of cellular structure,the fine structure of metals and crystalline materials as well as numerous other areas of the microscopic world.Although new inventions like the laser microscope may seem to put the use of electron microscopes under threat they will always play an integral part in determining the ultrastructure of cells. ?? ?? ?? ?? 1 ...read more.

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The candidate has used headings to split up the sections of information, which is fine, though their introduction is unclear and it reads more like a secondary paragraph. It is often easier to leave your introduction until last, that way ...

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Response to the question

The candidate has used headings to split up the sections of information, which is fine, though their introduction is unclear and it reads more like a secondary paragraph. It is often easier to leave your introduction until last, that way you can make it clear to the reader exactly what your plan to discuss, which is the main point of your introduction. You also need to include a brief description of you topic, in this case you should describe what a microscope is and what it used for. As the title of this essay is ‘Describe the principles and limitations of transmission and scanning electron microscopes’ it is strange that the candidate starts off by discussing optical microscopes, this actually left me feeling quiet confused about the purpose of this essay. This is another reason why it is so important to state what you plan to discuss in your introduction.

Level of analysis

The candidate gives a reasonable amount of detail on each type of microscope and they have clearly discussed the limitations for each. However they could have made the this essay more interesting to read by providing diagrams or images of the microscopes, by doing this you can refer to the images when discussing specific parts such as lens and this can help the reader understand what you are talking about. In addition to this the candidate could also have taken the time to undergone independent research, perhaps on the history of the microscope and how they were developed, this extra information shows interest in your subject and can make the essay more enjoyable to read. Finally, though the candidate has written a suitable conclusion, they have failed to summarise their key points, this is useful as it helps to tie together any lose ends and bring the essay to a close. In addition to this you are more likely to leave the reader with a good impression of your work if you write a personal reflection into your conclusion, this is because your teacher/examiner is interested in what you have to say and what you have learnt by writing your essay.

Quality of writing

The quality of the writing in this essay is only average, at times it is difficult to read and it feels more like an amalgamation of facts, therefore the essay does not flow as well as it could. You could improve this by taking the time to write out a plan and carefully thinking about what you want to say, it is also important to make sure that you spilt your writing up in paragraphs, do no simply write everything on one topic into a single paragraph, the general rule of thumb is that you should start a new paragraph when you begin discussing a new point/idea. In addition to this there are one or two spelling errors which could have been avoided had the candidate taken the time to carefully proof read their work.

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