1. What are the advantages and disadvantages of the different types of light and electron microscopes discussed in Chapter 3 that are used to study microorganisms? Focus your response in terms of the following parameters: o Range of magnification o Resolving ability o Sample preparation o Possible states of sample (e.g. whole organism, part of, living, non-living, etc
Compound Light microscopes magnification is 2000X. Resolution of about 0.2μm. Can only see very small specimens and specimens are stained.
Darkfield – used to study live microorganisms that cannot be stained or staining distorts the image or they are invisible using the normal light microscope.
Phase-Contrast – in living microorganisms, this scope allows you to see detailed internal structures, plus you do not have to fix or stain the microbes.
Differential Interference Contrast (DIC) – instead of one beam of light, 2 beams are used. Image looks almost 3-dimensional and is brightly colored.
Fluorescence – used mainly as a diagnostic technique. Stained with fluorochromes and viewed with an ultraviolent light.
Confocal – makes 3-dimensional images using a computer. Able to see entire cells and their components.
Two-Photon – living cells can be seen up to 1mm (1000um) deep in tissues. Can also track, in real time, the activity of cells.
Scanning Acoustic – living cells that are attached to cancer cells, artery plaque and biofilms can be seen through this scope with the use of sound waves.
Electron Microscopy – viruses or internal structures of cells that are less than 0.2um would use this scope to get images. Magnification is 10,000 to 100,000x. Resolving power is 10 pm. Images are always black and white.
Transmission Electron – resolving power is 10pm, magnification is 10,000 to 100,000. Positive and negative staining is used.
