Biology: Semester I |
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| Section: | Section 1 |
| Section One: | Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 |
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Biology: Cell Structure Size Matters View the presentation below to learn more about the microscopes. Be sure your volume is set to a reasonable level. Take notes as you are required to know this material.
After you have completed this section, you will be able to:
How big is a cell? Have you even seen a cell for that matter? If you had an egg for breakfast, you ate a single cell. So then, how big is a typical chicken egg? What about an ostrich egg? Most cells are microscopic. They cannot be seen with the naked eye. Microscopes are important tools for studying cells and cellular structures. There are several types of microscopes biologists use. Typically they use lighted microscopes for laboratory observations. The basics of different microscopes will be reviewed later. There are many different types of microscopes used in studying biology. These include the light microscopes (dissecting and compound), electron microscopes (transmission and scanning), and atomic force microscopes. This course will show light photomicrographs (pictures taken with a light microscope) and electron micrographs (pictures taken with an electron microscope). There are many terms and concepts that will help you in maximizing your study of microscopy. In the picture below, you can see a comparison of the scale of images that can be viewed by the electronic microsope, light microscope, and the naked eye.
Magnification and resolution are terms used frequently in the study of cell biology. Magnification is a ratio of the enlargement (or reduction) of an image usually expressed as X1, X1/2, X430, X1000, and so on. If the light passes through two microscope lenses (an objective lens and an ocular lens) we multiply the 10X ocular lens magnifying power by the power of the objective lens (say it is 4X): 10 X 4 = 40, or 40X magnification. Resolution is the capability to distinguish between two points. Generally resolution increases with increased magnification. What microscopes do is to bring small objects "closer" to the observer by increasing the magnification of the sample. Since the sample is the same distance from the viewer, a "virtual image" is formed as the light (or electron beam) passes through the magnifying lenses. Objects such as human hair appear (and feel) smooth when viewed with the unaided eye. However, put a hair under a microscope and it takes on a VERY different look due to the increased resolution of the microscope over the unassisted eye.Scientists employ the metric system to measure the size and volume of specimens. The basic unit of length is the meter (slightly over 1 yard). Prefixes are added to the "meter" to indicate multiple meters (kilometer) or fractional meters (millimeter). Below are the values of some of the prefixes used in the metric system.
The basic unit of length is the meter (m). One meter is slightly longer than an English yard. The metric measure of volume is the liter (l) and of mass it is the gram (g). Prefixes listed in the table above can be applied to all of these basic units, abbreviated as km, kg, ml, mg, nm,etc. The Greek letter micron (µ) is applied to small measurements (thousandths of a millimeter), producing the micrometer (symbolized as µm). Measurements in microscopy are usually expressed in metric terms. General units you will encounter in biology include micrometer (µm, 10-6m), nanometer (nm, 10-9m), and angstrom (Å, 10-10m).
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