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1 LAB EXERCISE 2 – MICROBES, ARE THEY “GOOD” OR “BAD”? ANSWERS OBJECTIVES: Learn to make scientific observations, draw and describe what you see. Learn the skill of microscopy correlating it with the size of an organism. Learn how microscopes and stains can be used to distinguish among different types of microbes. Explain why the identification of pathogenic microbes is important for treating diseases. Distinguish between different types of prokaryotic and eukaryotic cells. Identify microbes ( Bacteria, Protists (Protozoan), Fungi) Use these skills to identify the microbe that caused the “soft rot” in the potatoes (Lab 1). Why do we need microscopes to study microbes? With the naked eye, we cannot discern objects smaller than 200 ! m ( Sadava et al. p70). The typical compound light microscope is capable of increasing our ability to see detail by 1000 times so that objects as small as 200 nanometers (nm) can be seen. Electron microscopes extend this range further allowing us to see objects as small as 0.5 nm in diameter or roughly 1/200,000th the size we can see with a naked eye. Needless to say, development and use of microscopes has vastly improved our understanding of cells and their structure and function. Two important characteristics of microscopy are magnification and resolution. Magnification is simply a function of making an object appear bigger, such as when we use a hand lens to enlarge printed word. Merely magnifying an object without a simultaneous increase in the amount of detail seen will not provide the viewer with a good image. The ability of a microscope (or eye) to see detail is a function of its resolving power or resolution. Resolving power is defined as the minimum distance between two objects when the objects can just be distinguished as separate; it is a function of the wavelength of light used and the quality of the optics. In general, the shorter the wavelength of the light source, the higher the resolution of the microscope. Electrons have a shorter wavelength than light. Consequently, better resolution with the electron microscope. What are the important parts of a compound light microscope? (Parts may vary slightly in each room.) Use the picture at the end of this document to find the parts of the microscope. 1. Ocular lens or eyepiece : The oculars that you will be looking into in lab are 10X (10 times) magnification. The oculars themselves magnify the object 10 times. The microscopes you will use are binocular (two eyepieces). The two eyepieces do not, however, serve to double the magnification. 2. Body tube: contains mirrors and prisms, which direct the image to the ocular lenses. 3.
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This note was uploaded on 10/18/2011 for the course CHEMISTRY 209 taught by Professor Cohen during the Spring '11 term at Pittsburg State Uiversity.

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