Goals: Student Learning Outcomes: Upon completion of this lab, students will be able to: In Biology, the compound light microscope is a useful tool for studying small specimens that are not visible to the naked eye. The microscope uses bright light to illuminate through the specimen and provides an inverted image at high magnification and resolution. There are two lenses that magnify the image of the specimen – the objective lens on the nosepiece and the ocular lens (or eyepiece). To determine the total magnification of the specimen, you must multiply the objective lens magnification with the ocular lens magnification. Scientists and technicians often use light microscopes to study cells. Prokaryotic cells are very simple and lack a nucleus or membrane bound organelles and are small in size. On the other hand, eukaryotic cells are more complicated in that they contain a nucleus and many specialized organelles. A cell’s structure dictates its function; thus, each eukaryotic cell looks very different from the next. This is why a cardiac cell looks completely different from a neuron (brain cell). It is very important to learn how to handle and use a microscope properly. Review the following rules and tips for using and handling your microscope. If needed, obtain a small square of lens paper (and ONLY lens paper) and gently wipe the microscope lenses directly across, in this order:
Identify the following microscope parts with a partner. Check off each part as you go. If you are unsure about a component, consult your instructor.
When finished with the slide, lower the stage and remove the slide. (Do not lower the stage if you are going to view a different slide). Clean the oil off the slide and return it to your instructor.
Microscopes are for magnification of images too small to be seen with the naked eye. However, they can be used as a tool to estimate the size of the object being viewed. In order to do this, you must know the diameter of each viewing field with each objective lens. You can then estimate how much of the field your object takes in the field and compare this to the measured diameter. For example, let’s say the diameter of field using the 40x objective lens is 0.10 mm. You then view an object using that lens that takes up ¼ of the field of view. You can then estimate that object is ¼ (0.10mm) long or 0.025mm. To determine the field diameter, you will use a stage micrometer slide, which is basically a very fine ruler (usually 2 mm) that is etched onto a microscope slide. Figure 2. Stage micrometer
Figure 3. Human cheek cell at 400x zoom. The human cheek is lined with epithelial cells. They will be used today for you to observe a eukaryotic animal cells and its nucleus. You will scrape and stain a sample of your cheek cells with the dye methylene blue. The dye will allow you to clearly stain the nuclei of the cells. Be careful with the dyes used for the wet mounts as they will stain your skin and clothes. Also, the slides and coverslips you will use are stored in alcohol. Make sure to dry off the slides and coverslips with paper towels (not the expensive lens paper) before preparing your wet mount slides.
The cell membrane is not visible on the Elodea leaf because of its proximity to the much thicker cell wall. In order to view the membrane, you will add salt to the Elodea. Water will flow out of the Elodea cells by osmosis, shrinking the cell membrane away from the stiff cell wall (plasmolysis).
Figure 4. Elodea cells at 400x Figure 5. Elodea cells undergoing plasmolysis at 400x
Onion bulbs are actually swollen leaves that form an underground structure. Although not a good source for viewing chloroplasts, they are an excellent source for viewing eukaryotic plant nuclei. Figure 6. Onion cells at 400x
You will prepare a wet mount of one of the following protists that can be found in pond water: Euglena, Spirogyra, Paramecium, and/or Amoeba.
You will look at various prepared slides including Paramecium, Spirogyra, Human Blood Smears, Human Sickle Cell Red Blood Smears, Frog Blood Smears, and possibly others. View under the microscope using the highest magnification for the best cellular details and draw what you see. Be sure to indicate the magnification used and specimen name. Also, indicate the estimated cell size in micrometers under your drawing. Figure 7. Specimens at 400x Magnification.From left to right: Spirogyra, Paramecium, Human Blood Smear, Human Sickle Cell.
Check off each task when complete. The instructor must sign before storing your microscope.
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