Light Microscopy - Basic Skills of Light Microscopy While...

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1 Basic Skills of Light Microscopy While we can readily see many organisms throughout the living world, the biological structures within those organisms and even a greater number of whole organisms remain invisible to the naked eye. The most common tool for examining these objects that are so tiny is a light microscope . This device is a series of glass lenses within tubes that produce a larger, focused image of the specimen on the retina of your eye or on a projection screen. The most important property of a microscope is that it magnifies the specimen – it increases its apparent size. A telescope does the same thing for objects that are very far away. But just enlarging the specimen is not sufficient to examine the inner structure of a complex cell, it must be accompanied by an increase in resolution . Resolution is defined as the ability to distinguish two points as separate individuals. From far away you see a tree in the distance as a blotch of green, with a telescope you can center in on that tree and see that the green is actually a collection of individual, distinct leaves. If the telescope, or microscope, just increased magnification without increasing resolution, the green blotch would simply look like a larger green blotch. An increase in resolution makes the image look sharper or crisper and more detail is discernable. The resolving power of the naked eye is about 0.1 mm, that means that the average human eye can distinguish two dots that are only 0.1 mm apart. You should easily be able to see these two periods . . as separate individuals and as they are separated by about 1.0 mm. A good quality light microscope improves image resolution by about 1000-fold (that is, to a value of 0.0001 mm = 0.1 μ m) Greater magnification and resolution are often not enough in themselves to make the invisible visible. Biologists often employ dyes and stains to highlight organisms or specific parts of cells. These stains may simply increase the contrast of the object against the background, as you will examine when you observe your own cheek cells. Many stains additionally have a specific affinity for certain parts of a cell. You will examine this next week when you Gram stain bacteria. Although Robert Hooke coined the name “cell” in the 15th century to describe the honeycomb sections in a slice of cork, it wasn’t until two centuries later that the universality and importance of cells was understood. Improvements in lens design and the light microscope in the early 1800’s enabled biologists to observe living organisms in much finer detail. Structure of the Microscope Light microscopes are typically composed of at least two systems: an illuminating system and an imaging system. They may additionally have a viewing and recording system in the form of a still or video camera and projector or TV screen. The illuminating system concentrates light on a specimen, like a flashlight shining on a doorknob in a
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This note was uploaded on 10/13/2011 for the course BIO 1510 taught by Professor Rodriguez during the Fall '08 term at Wayne State University.

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Light Microscopy - Basic Skills of Light Microscopy While...

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