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Microscopy. History of the microscope:-

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Introduction

Microscopy

Microscopes are tools which allow us to see objects which we cannot see with the naked eye. There are two main types of microscopes used nowadays. These are light microscopes and electron microscopes.

During the 16th century the microscope was invented, which was of great assistance to works in medicine and biology. At first, the microscope was basically used recreationally, and was found in the homes of wealthy people. However, not long afterwards, proper uses for the microscope were discovered, and so study of bacteria and diseases began.  

History of the microscope:-

  • Circa 1000AD – First vision aid was invented called a reading stone. It was a glass sphere that magnified when laid on top of reading materials.
  • Circa 1284 - Italian, Salvino D'Armate invented the first wearable eye glasses.
  • 1590 – Zaccharias Janssen and his son Hans Janssen experimented with multiple lenses in a tube and observed that objects appeared greatly enlarged
  • 1665 – Robert Hooke noticed some "pores" or "cells" in a sliver of cork looking through a microscope.
  • 1674 – Anton van Leeuwenhoek built a simple microscope with only one lens to examine blood, yeast, insects and other tiny objects. He invented new methods for grinding and polishing microscope lenses that allowed for curvatures providing magnifications of up to 270 diameters, the best available lenses at that time. image00.jpg

                                                            Leeuwenhoek’s microscope

  • 1872 – Ernst Abbe wrote a mathematical formula - "Abbe Sine Condition". His formula provided calculations that allowed for the maximum resolution in microscopes possible.
  • 1903 – Richard Zsigmondy developed the ultra microscope that could study objects below the wavelength of light.
  • 1932 – Frits Zernike invented the phase-contrast microscope that allowed for the study of colourless and transparent biological materials
  • 1931 – Ernst Ruska co-invented the electron microscope.
  • 1981 – Gerd Binnig and Heinrich Rohrer invented the scanning tunnelling microscope that gives three-dimensional images of objects down to the atomic level. Binnig and Rohrer won the Nobel Prize in Physics in 1986. The powerful scanning tunnelling microscope is the strongest microscope to date.
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Middle

X200, 000

Best resolution

200 nm

0.5 nm

Image formed

Colour

Monochrome -black & white

Different types of microscopes have been used to look at human cells, identify minerals, solve crimes, see how freezing affects food, study metals, and also find the causes of crop diseases. Microscopes are an essential tool in medicine too. They have been used to identify the causes of many deadly diseases like malaria and tuberculosis. Microscopes can also help to find out why a person or animal died.

Types of microscopes:-

Compound

Dissection or stereoscope

Confocal microscope

Scanning Electron Microscope (SEM)

Transmission Electron Microscope (TEM)

Description

Compound microscopes are light illuminated. The image seen with this type of microscope is two dimensional. This microscope is the most commonly used. You can view individual cells, even living ones. It has high magnification. However, it has a low resolution.

A dissection microscope is light illuminated. The image that appears is three dimensional. It is used for dissection to get a better look at the larger specimen. You cannot see individual cells because it has a low magnification.

This microscope uses a laser light. This light is used because of the wavelength. Laser light scan across the specimen with the aid of scanning mirrors. Then image is then placed on a digital computer screen for analyzing.

SEM use electron illumination. The image is seen in 3-D. It has high magnification and high resolution.

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Conclusion

The samples have to be viewed in a vacuum, as the molecules that make up air would scatter the electrons. Recent advances have allowed hydrated samples to be imaged using an environmental scanning electron microscope.

The samples have to be prepared in many ways to give proper detail.

Samples viewed under an electron microscope may be treated in many ways:

  • Cryofixation - freezing a specimen so rapidly, to liquid nitrogen or even liquid helium temperatures, that the water forms vitreous (non-crystalline) ice. This preserves the specimen in a snapshot of its solution state.
  • Fixation - preserving the sample to make it more realistic. Glutaraldehyde - for hardening - and osmium tetroxide - which stains lipids black - are used.
  • Dehydration - replacing water with organic solvents such as ethanol or acetone.
  • Embedding - infiltration of the tissue with a resin such as araldite or epoxy for sectioning.
  • Sectioning - produces thin slices of specimen, semitransparent to electrons. These can be cut on an ultramicrotome with a diamond knife to produce very thin slices.
  • Staining - uses heavy metals such as lead, uranium or tungsten to block electrons to give contrast between different structures, since many materials are nearly "transparent" to electrons.
  • Ion Beam Milling - thins samples until they are transparent to electrons by firing ions (usually argon) at the surface from an angle and sputtering material from the surface.

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Here's what a star student thought of this essay

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Response to the question

The candidates introduction starts off well, they introduce the term light microscope, they explain what a microscope is and what it is used for. This is very good, however an introduction should also clearly state exactly what you plan to ...

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Response to the question

The candidates introduction starts off well, they introduce the term light microscope, they explain what a microscope is and what it is used for. This is very good, however an introduction should also clearly state exactly what you plan to discuss so that the purpose of your essay is clear. That said the candidate gives a very detailed account of the different types of microscopes and has used appropriate technical terms throughout.

Level of analysis

The candidate uses bullet points to state the relevant facts relating to the development of microscopes, and they have put together a table to show the comparison of different types of microscopes, while is fine for your notes for even an essay plan, it is not something that I would encourage you to include in an essay. It is more appropriate to write this type information in a paragraph so that you can provide further detail. At this level of qualification you should be able to write scientific information in prose. That said the candidate does provide a great deal of information and has possibly undergone independent research, which shows interest and dedication in your subject and can make your essay more enjoyable to read. Unfortunately though, there is no conclusion to this essay, this is a mistake, without a clear conclusion, your essay ends abruptly, whereas if you take the time to summarise your key points and include a personal response you can leave the reader with a good impression of your work.

Quality of writing

The candidate has accurately used scientific terms, with the exception of the term light microscope which is more accurately described as an optical microscope and this is term I would expect and A-level candidate to use. However the essay is coherent and it is clear that the candidate understands the topics they are discussing. Though there a few spelling errors, which possibly could have been avoided if the candidate had thoroughly proof read their work.


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