Microscopy Introduction
The size of a typical bacterium is about 1000 times smaller than a millimeter, one micron! It's easy to see why special instruments are needed to view these tiny organisms. An extremely useful tool for the microbiologist is a microscope. Many types of microscopes exist, yet the most often used are the light microscope, the transmission electron microscope (TEM), and the scanning electron microscope (SEM). These three types of microscopes differ in two major ways- the illuminating source and the type of image obtained.
The light microscope utilizes photons, or visible light, as illumination while the electron microscopes take advantage of the low-wavelength electron. Because of the low wavelength (high frequency) of the electron particle, the resolution of the electron microscope in many times greater than that of the typical light microscope.
All three microscopes offer different images of varying quality and detail. Each reveals different aspects of microorganisms and rarely is only one type of microscope ever sought for research purposes. For example, the light microscope is useful for identifying cell morphology easily and counting, while the TEM is useful for ultrastructural (cell wall, cell ionclusions) aspects of cells and the SEM for detailed surface structures. However, preparation for electron microscopy is often long and requires much skill.
How are the following images taken and what can they tell us about microorganisms?
Light  |
Transmission EM  |
Scanning EM  |