Vocabulary

compound light microscope eyepiece (ocular lens) objective lens stage light source magnification nosepiece resolution scanning electron microscope transmission electron microscope metric system base unit

figure 1-13

Compound light microscopes open the human eye to an interesting world including tiny pond organisms, healthy and diseased cells, and the functioning of cell parts.

figure 1-13

Compound light microscopes open the human eye to an interesting world including tiny pond organisms, healthy and diseased cells, and the functioning of cell parts.

Magnification and Resolution

Microscopes vary in powers of magnification and resolution. Magnification is the increase of an object's apparent size. Revolving the nosepiece, the structure that holds the set of objective lens, rotates these lenses into place above the specimen. In a typical compound light microscope, the most powerful objective lens produces an image up to 100 times (100x) the specimen's actual size. The degree of enlargement is called the power of magnification of the lens. The standard ocular lens magnifies a specimen 10 times (10x ). To compute the power of magnification of a microscope, the power of magnification of the strongest objective lens (in this case, 100 x) is multiplied by the power of magnification of the ocular lens (10x ). The result is a total power of magnification of 1000x.

Resolution (REZ-uh-LOO-shuhn) is the power to show details clearly in an image. The physical properties of light limit the ability of light microscopes to resolve images, as shown in Figure 1-14a. At powers of magnification beyond about 2,000x, the image of the specimen becomes fuzzy. For this reason, scientists use other microscopes to view very small cells and cell parts.

Electron Microscopes

To examine cells in more detail or to view cell parts or viruses, scientists can use other microscopes, such as an electron microscope. In an electron microscope, a beam of electrons produces an enlarged image of the specimen. Electron microscopes are more powerful in magnification and resolution than light microscopes. Some electron microscopes can even show the contours of individual atoms in a specimen. Electron microscope images are always in black and white. However, scientists can use computers to add artificial colors to help identify structures in the image. Also, the specimen must be placed in a vacuum chamber. Because cells cannot survive in a vacuum, electron microscopes cannot be used to view living specimens.

There are two main types of electron microscopes. The first type of electron microscope is the scanning electron microscope (SEM). The SEM passes a beam of electrons over the specimen's surface. SEMs provide three-dimensional images of the specimen's surface, as shown in Figure 1-14b. First, the specimen is sprayed with a fine metal coating. Then, a beam of electrons is aimed at the specimen, which causes the metal coating to emit a shower of electrons. These electrons project onto a fluorescent screen or photographic plate. The result is an image of the object's surface. SEMs can magnify objects up to 100,000 times.

The second type is the transmission electron microscope (TEM). The TEM transmits a beam of electrons through a very thinly sliced specimen. Magnetic lenses enlarge the image and focus it on a screen or photographic plate. The result is an image such as the one shown in Figure 1-14c. Note the great resolution of the paramecium's internal structure. Transmission electron microscopes can magnify objects up to 200,000 times.

(a) Paramecium (light microscope)
(b) Paramecium (scanning electron microscope)

(c) Paramecium (transmission electron microscope)

figure 1-14

The images above show a Paramecium as viewed under three different types of microscopes. (a) Light microscopes can produce an image that is up to 1,000 times larger than the actual specimen. (b) Scanning electron microscopes produce images up to 100,000 times larger than the specimen. SEMs provide a view of surface features. (c) Transmission electron microscopes produce images up to 200,000 times larger than the actual specimen.

(c) Paramecium (transmission electron microscope)

figure 1-14

The images above show a Paramecium as viewed under three different types of microscopes. (a) Light microscopes can produce an image that is up to 1,000 times larger than the actual specimen. (b) Scanning electron microscopes produce images up to 100,000 times larger than the specimen. SEMs provide a view of surface features. (c) Transmission electron microscopes produce images up to 200,000 times larger than the actual specimen.

TABLE 1-1 SI Base Units

Base quantity

Name

Abbreviation

Length

meter

m

Mass

kilogram

kg

Time

second

s

Electric current

Sirens Sleep Solution

Sirens Sleep Solution

Discover How To Sleep In Peace And Harmony In A World Full Of Uncertainty And Dramatically Improve Your Quality Of Life Today! Finally You Can Fully Equip Yourself With These “Must Have” Tools For Achieving Peace And Calmness And Live A Life Of Comfort That You Deserve!

Get My Free Ebook


Post a comment