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Many biological specimens such as cells and tissues are difficult or impossible to be seen with the naked eye so they must be magnified to be studied. Consequently, the basic operation and care of microscopes is an important skill in biology.

Electron microscopes are expensive and require special training. Even though the preparation techniques used to prepare specimens for electron microscopy kill most living cells, some cells such as Tardigrades can withstand these harsh treatments.

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Located on the revolving nosepiece. Each lens has a different magnifying power. The smallest objective (scanning objective) is the smallest magnification at 4x, followed by the low power objective at 10x, the high power objective at 40x, and the highest magnification (immersion oil objective) at 100x. Only one objective may be used at a time. The selected lens is rotated into position by turning the nosepiece.

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Two basic types of microscopes are used in our introductory biology labs: compound light microscopes and stereo microscopes (aka dissecting microscopes).

Stereo microscopes (also called dissecting microscopes; Figure 2) also contain 2 sets of lenses (ocular and objective lenses). The ocular lenses on a stereo microscope, like a compound light microscope, magnify by a factor of 10x. The objective lenses, however, have relatively low magnification. There is a great deal of variation in stereo microscopes and the manner in which they achieve higher magnification. Stereo microscopes include an additional magnification system that makes the final image appear to be upright.

The lens in the upper part of the microscope. Monocular microscopes have one ocular, while binocular microscopes have two oculars. Ocular magnification is 10x.

Located on either side of the arm. Moves the stage to bring the object into focus. This knob should only be used when the scanning (4x) objective is positioned above the stage!

They are used for viewing and manipulating relatively large specimens which can be viewed in three dimensions. They have a binocular feature that creates a stereoscopic effect. They can be used to study entire small organisms since their depth of field is much greater than the compound light microscope. The light source can be directed down onto a specimen (reflected light) as well as up through the specimen (transmitted light), which permits the viewing of objects too thick to allow for the transmission of light. It is also possible to view multiple samples in a petri dish placed on the microscope’s stage with light that is projected from below.

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Transmission electron microscopes are used to study internal cell structure and are analogous to compound light microscopes in that regard. Specimens are cut into thin sections, usually “stained” with heavy metal atoms (atoms with large atomic numbers) that attach to cell structures. An electron beam is then focused through the specimen. Figure 3 is an example of the type of image an electron microscope can produce.

Since the scanning objective is 4x and the low power objective is 10x, images will be magnified more with low power than with scanning power. Because objects will appear larger, the low power “field of view” will be smaller than the scanning power field. Therefore the relationship between the diameter of the field of view and the magnification is inversely proportional. Not only does measuring the field of view at different magnifications demonstrate this property, but once you know the diameter of the field of view in millimeters (mm) at various magnifications, you will be able to estimate the size of the cells or other structures being viewed.

This page titled 1.2: Microscopes is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Brad Basehore, Michelle A. Bucks, & Christine M. Mummert via source content that was edited to the style and standards of the LibreTexts platform.

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Compound light microscopes pass visible light through two sets of magnifying lenses (the ocular and the objective lenses) to magnify specimens mounted on a glass slide and placed on the flat surface (stage) of the microscope. The specimens must be sliced very thin in order for light coming from the light source to pass up through them so that they can be viewed. Specimens are sometimes stained with dyes to add contrast and to make structures more easily identifiable. Microscopic examination of cells and tissues allows students to observe the principle of complementarity - how cell and tissue structure determines function.

Upper part of microscope that extends from arm and contains the ocular lenses and revolving nosepiece with objective lenses.

Scanning electron microscopes, analogous to stereo microscopes, allow a specimen’s surfaces to be observed in detail. The object is chemically frozen and then coated with a thin film of metal. An electron beam excites surface electrons on the specimen and produces a three-dimensional image. Figure 4 is an example image that is produced by an SEM.

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According to the cell theory, the cell is the fundamental biological unit, the smallest and simplest biological structure which possesses all of the traits of something that is living. All living organisms are composed of one or more cells, and every activity taking place in any living organism is ultimately related to the metabolic processes that are taking place in cells. Therefore, to understand the processes of life, it is necessary to understand the structure and function of the cell. Cells that line the interior of the mouth and cheeks are situated very close together, similar to tiles on a floor. These thin cells form a thick layer that protects the underlying tissue from abrasion and foreign pathogens (e.g. viruses and bacteria). The cells comprising the most superficial layer are continually sloughed off and replaced by underlying cells. Gently scraping the lining of the cheek removes the superficial cells. In this activity, you will prepare a wet mount slide of cheek cells and observe them under the compound light microscope.

Depth of field is the area (top to bottom) of an object that comes into focus while slowly moving the fine adjustment knob up and down. Because the depth of focus is very short in the compound microscope, you must focus up and down to clearly view all of the planes of a specimen.

In this exercise, you will identify and learn the functions of various microscope parts. Proper practice for handling and use of compound light microscopes is as follows:

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Electron microscopes, first developed in the 1940s, use a beam of electrons instead of light to magnify an object. They can magnify objects as small as 2 nanometers (0.00000004 inches) over 100,000 times.

Leaves of Elodea, a common aquatic water plant, are great for observing the major characteristics of a typical plant cell. In this activity you will prepare a wet mount and examine one of the leaves from the Elodea under the compound light microscope.

Belwood, Jacqueline; Rogers, Brandy; and Christian, Jason, Foundations of Biology Lab Manual (Georgia Highlands College). “Lab 3: Microscopy,” (2019). Biological Sciences Open Textbooks. 18. CC-BY https://oer.galileo.usg.edu/biology-textbooks/18

The optics of a light microscope’s lenses change the orientation of the image the user sees. A specimen that is right-side up and facing right on the microscope slide will appear upside-down and facing left when viewed through a microscope, and vice versa. Similarly, if the slide is moved left while looking through the microscope, it will appear to move right. If moved down, it will seem to move up. This occurs because microscopes use two sets of lenses to magnify the image. Because of the manner by which light travels through the lenses, this system of two lenses produces an inverted image.

Moveable part of the stage controlled by stage adjustment dials located below the stage. Allows the observer to move the stage forwards, backwards, left, and right.