11964250
Descripción
Fichas por Calla Frederiks, actualizado hace más de 1 año
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Creado por Calla Frederiks
hace casi 7 años
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| Pregunta | Respuesta |
| Microscope | an invaluable tool used for observing objects that can not be seen by the naked eye; enables us to view the ultrastructure (fine detail) of organisms, cells, and tissues. |
| compound light microscope | magnifies objects from 40 to 1000 times its original size specimens must be either small objects of very thinly cut sections of an object; translucent allowing light to be transmitted through them |
| dissecting (stereoscopic) microscope | magnifies objects from 4 to 50 times specimens are usually opaque |
| Normal Procedure to prepare a specimen for most staining protocols | allow the organisms to dry to a glass slide; pass the slide through the Bunsen burner flame in order to fix the organisms to the slide |
| Problems with this procedure and why | This procedure does not allow one to visualize the cells in their natural state. The size and shape of the cell may become distorted. Also, heat-fixing removes the water from the cell which affects the size of the cell when viewed under the microscope |
| Pros to Negative Staining | allows one to view living organisms that have not been heat-fixed to a slide; allows one to visualize organisms or parts of organisms, such as a capsule, which may not readily take up stains |
| Negative Staining characteristics | The background is filled with a stain (such as India ink or nigrosin) while the organisms remain clear, unstained objects that stand out clearly against this dark background. |
| The "why" behind the cells appearing clear when stained | These stains (negative stains) do not penetrate the bacterial cells due to the repulsion between the negative charge of the stains and the negatively charged bacterial cell. |
| Two different methods to prepare negative stains | a suspension of bacterial cells is emulsified in a drop of nigrosin (India ink) and covered with a cover slip (wet mount) or allowed to air dry (smear) |
| Most microorganisms appear ______ when viewed through a ___________ _______ microscope. | colorless; brightfield light |
| Most common method method of allowing visualization of microorganisms under a microscope is to ... | stain, or color them. |
| Staining _________ to the microorganisms so that various structures can be observed | imparts color |
| How to prepare a bacterial smear | A drop of liquid bacterial culture or a drop of water and a portion of a bacterial colony is spread over the surface of the slide |
| Important facts about preparing the bacterial smear | one loopful of liquid bacterial culture usually provides sufficient bacteria for easy viewing REMEMBER 1 bacterial colony = millions of individual bacteria When mixing water with the bacteria only a small drop of water is needed |
| Why is only a small amount of water needed? | the smears are air-dried, the more liquid, the longer the smear will take to dry |
| When mixing the bacteria with the water to create the smear... | avoid overmixing because this can lead to inaccurate bacterial cell patterns (chains may appear as clumps and vice versa) |
| Once the smear has air-dried, the next step is to | heat-fix the slide |
| Heat-fix | The air-dried smear is briefly passed through the Bunsen burner flame 2 or 3 times. |
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