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Introduction

Microscopy The website www.rifelabs.com/glossary.html defines microscopy as the science of studying a subject under a microscope, the subject being a minute object too small to otherwise be seen by the naked eye. The microscope is vital instrument in Cell Biology, since the human eye has a resolving power of 1/10 of a millimetre. Resolution The diameter of the ekaryotic cell varies from 10 - 30 �m (micrometers), and even smaller in the prokaryotic cells, this size is not visible by the naked eye, therefore microscopes are used to provide a better resolution. "Resolving power (resolution *) is the measure of the capacity to distinguish one another; it is the minimum distance that must be between two objects for them to be perceived as separate object." Magnification It is the number of times larger an image is compared with the real size of the object. It can be calculate using the formula below: Magnification = size of image . Actual size of specimen (1) The three types of microscopes are the light microscope, the transmission electron microscope and the scanning electron microscope. This assignment looks at the development and the differences of each microscope. ...read more.

Middle

They are then magnified by a series of magnetic lenses until they hit photographic plate or light sensitive sensors - which transfer the image to a computer screen. The image produced is called an electron micrograph (EM). The transmission electron microscope goes beyond the resolution of the light microscope and has been the main factor and instrument in assembling and gaining all the information about the cells and its organelles. The electron microscope uses electrons instead of light to produce a magnification of minute details with very high resolving power. Electrons allow the TEM to magnify in higher resolution because of their short wavelengths, in contrast to the light's longer wavelength. Because of these factors that Ernst Ruska considered when developing the TEM, the electron microscope can therefore magnify up to 500,000 times. Below is evidence of the detail the electron microscope can produce The Scanning Electron Microscope This new device was developed from the basis of the transmission electron microscope. Gerd Binnig and Heinrich Rohrer shared half of a Nobel Prize for their development of the scanning electron microscope. Differences Between Scanning Electron Microscope and Transmission Electron microscope. ...read more.

Conclusion

The short wavelength of electrons enables the electron microscope have high resolving power. However the electron has many disadvantages, as it costs over �1 million, and is also expensive to produce electron beam. It is large and bulky (refer to figure 1.3) and requires a special room. Finally, a vacuum is also needed to carry out the magnification. Below is a table summarising the above paragraphs. LIGHT MICROSCOPE ELECTRON MICROSCOPE Cheap to purchase (�100 - 500) Expensive to buy (over � 1 000 000). Cheap to operate. Expensive to produce electron beam. Small and portable. Large and requires special rooms. Simple and easy sample preparation. Lengthy and complex sample prep. Material rarely distorted by preparation. Preparation distorts material. Vacuum is not required. Vacuum is required. Natural colour of sample maintained. All images in black and white. Magnifies objects only up to 2000 times Magnifies over 500 000 times. (5) Reference: Figure 1.1: http://science.howstuffworks.com/light-microscope5.htm Figure 1.2: WS- Section A Molecules and Cells 3 Figure 1.3: http://www.phy.cuhk.edu.hk/centrallaboratory/CM120/CM120.jpg Figure 1.4: http://www.ogm-info.com/E.coli.jpg (1): (* Helena Curtis and N Sue Barnes 1989 Biology, The Fifth Edition W.H. Freeman, pages 94 - 99.) (2): (http://inventors.about.com/library/inventors/blmicroscope.htm) (3,4): http://www.mrothery.co.uk/cells/microscopynote.htm (5): Mary Jones, Richard Fosbery and Dennis Taylor (2000) Biology 1, Cambridge, Cambridge University Press, pages 3-10. ?? ?? ?? ?? ...read more.

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