Electrons have a much smaller wavelength than light. This means that they can pas between objects that are too close together to let light pass them. Therefore electrons can resolve objects that light cannot. Microscopes that use electron instead of light are called electron microscopes and can resolve to about 1nm (smaller than a haemoglobin molecule). There are two types of electron microscopes, transmission electron microscopes which pass beams of electrons through very thin objects and, scanning electron microscopes which beams of electrons of the surface of an object
(Indge, B etal 2000).
What can electron microscopes do?
Electron microscopes can tell us about four aspects of a specimen:
The surface features of an object or "how it looks", its texture. There is a direct relation between these features and materials properties (hardness, reflectivity...etc.)
The shape and size of the particles making up the object. This relates between their structures and materials properties (ductility, strength, reactivity...etc.)
The elements and compounds that the object is composed of and the relative amounts of them; direct relationship between composition and materials properties (melting point, reactivity, hardness...etc.)
Crystallographic Information
How the atoms are arranged in the object. We can deduce from this a relation between these arrangements and materials properties (conductivity, electrical properties, strength...etc.)
(www.unl.edu/CMRAcfem/em.htm, 13/10/02, University of Nebraska Lincoln)
It is clear to seen the advantage of the electron microscope with the comparison of these two slides
What have electron microscopes done for biology?
Although the electron microscope has advanced many different areas of science, the particular area biology that has been most helped has been the understanding of cell ultra structure or microbiology. Since the advent of the electron microscope the organelles we know about today, mitochondria, granular endoplasmic reticulum, golgi apparatus, lysomes, and other structures such as food stores, nucleic acids, cytoskeletons and membranes, have been discovered. Almost the knowledge we have of the structure and function of cell ultrastructure has come from electron microscopy.
It is difficult to exaggerate the impact that this instrument has had on biology. Materials, which were formally described as structureless, have been shown to have an elaborate internal organisation, and so-called homogeneous fluids are now known to contain a variety of complex structures. The electron microscope has opened up a new world whose existence was barely realized fifty years ago (Roberts, M etal 1993).
The understanding of the existence and function of these different structures has helped on practical aspects of biology such as medicine. The knowledge gain about cell ultrastructure has aided the treatment of diseases such as cancer and infection from viruses. Any work that relates to cells will make use information gained from electron microscopes. Electron microscopes are now also being used to analyse DNA and aiding the contemporary work on genetics.
Information from electron microscope has also provided evidence to support the theory of evolution as most cell share common components (1994-2001 Encyclopedia Britannica CD-ROM). In addition, in the forensic field, the scanning electron microscope is used to detect and analyse gunshot residue and other trace materials, such as paint, glass and light filaments (www.troopers.state.ny.us/ForSc/ModFor/E-Micro.html, 14/10/02, New York State Police Forensic Department).
Conclusion
In conclusion the electron microscope is a huge leap forward is microscopy as it has a mush larger resolving power, this has aided microbiologists greatly allowing them to see cell ultra structure as well as viruses and even analyse DNA. The principal part of what is known about cell ultra structure is thanks to the electron microscope. It allows for an understanding of all things small from insects, to bacteria, to DNA. I has also helped supported the theory of evolution and contributed to forensic science.
Bibliography
Indge,B etal
2000
A New Introduction To Biology
Hodder & Stoughton
ISBN 0 304 78167X
Iowa State University
mse.iastate.edu/microscopy/insects.html, 13/10/02
University of Nebraska Lincoln
www.unl.edu/CMRAcfem/em.htm, 13/10/02
Roberts, B etal
1993
Biology Principles and Processes
Thomas Nelson and Sons Ltd
ISBN 0-17-448176-4
Encyclopedia Britannica CD-ROM Deluxe Edition
1994-2001
New York State Police Forensic Department
www.troopers.state.ny.us/ForSc/ModFor/E-Micro.html, 14/10/02