In this laboratory you will learn how to correctly use the compound light microscope in observing bacterial (prokaryotic), animal (eukaryotic) and plant (eukaryotic) cells. Remember that careful and accurate observations are usually essential steps in the scientific method. For this we will be using a 3D simulation online, which will allow us to manipulate all the different controls and knobs just as on an actual microscope.
Open a separate browser window and go to this link: https://www.ncbionetwork.org/educational-resources/elearning/interactive-elearning-tools/virtual-microscope
When on the opening page, navigate to the middle of the page under the “Related Information”, and watch the five-minute video on the Use and Care of a Microscope. Make note of the various parts and the proper sequence of focusing on an object from lower to higher magnification. Refer to the labeled photograph of the microscope we use at College, and learn the names and functions of nine main parts.
Parts of the Microscope
LEICA DM500 MICROSCOPE
1) ocular (eyepiece) lens-magnifies the real image projected into the body tube. Our ocular lens magnifies the real image 10 times.
TOTAL MAGNIFICATION = ocular magnification x objective magnification
2) Revolving nosepiece-rotates so that the different objective lenses can be properly placed below the body tube. These PARFOCAL microscopes allow you to find a specimen (e.g., cell) at one magnification and to switch to another objective and still find the specimen in focus or very nearly in focus at the new magnification.
3) Objectives-lenses that magnify the specimen to produce a real image on a plane in the body tube. Each objective lens is marked with its magnification (e.g., 10X, 100X,). The only lens that ever has immersion oil placed on it is the oil immersion (100X) lens. The OIL MUST BE REMOVED from this lens with LENS PAPER before you return the microscope to the proper slot in the microscope cabinet.
4) Stage-holds the specimen/slide for observation.
5) Iris diaphragm lever-controls the amount of light passing through the specimen. You will generally want to increase the amount of light passing through the specimen as you increase magnification.
6) Light-function should be obvious!
7) Base-supports microscope. One hand is placed under it in carrying the microscope. The other hand is on the arm.
8) Course adjustment knob-used to focus the specimen with the 4, and 10 X objective lenses.
9) Fine adjustment knob-used primarily for fine focus of the specimen with the 40/45 and oil immersion objective lenses.
Once you have familiarized yourself with the various parts and the proper sequence of using the low to high magnification adjustment, launch the 3D simulation. Take a minute to familiarize yourself of the simulation setup. You can review the names of the various parts the microscope once more by selecting “Learn” from the choices below.
When you are ready to observe actual objects (cells and tissues in our case), select the “Explore” button. This will bring you to microscope setup with optical Oil and lens paper on the left, and a box of tissue and prepared slides on your right. The slide box is marked with a question mark; click on the “?”. This will open the slide Catalog. From the Slide Catalog you will select following specimens: (as you go through various cell type, record your observations)
1) Plant Slides: Select “Onion Root” (we will come back to onion root for lab on mitosis)
Observe the onion root from 4x all the way to 100x (oil immersion)
2) Animal Slides: Select “Whitefish Interphase” (we will come back to other whitefish slides for lab on mitosis)
Observe the whitefish embryo from 4x all the way to 100x (oil immersion)
3) Bacterial Slides: Select either the “Acid Fast Mix” or the “Gram Stain Mix”
Observe the Bacteria from 4x all the way to 100x (oil immersion)
4) Human Slides: Select the “Blood” and “Simple Squamous Epithelium”
Observe the Blood and Epithelium from 4x all the way to 100x (oil immersion)
Based on your observations from the simulation, answer following questions
1.Of the five different cell types you observed, list two types that looked most like one another? What structural features do your choices have in common?
2. Which cell was the smallest? _______________
Which cell was the largest? ________________
3. Were all the cells in the onion root the same length?
YES NO (Highlight/underline one)
4. Name the dark, linear, thread-like structures that you can see in some of the onion root tip cells. What Biomolecule of heredity do they contain?
5. Comparing bacteria, amoeba and human epithelial cells?
Name two cell components(parts) that bacteria, amoeba and human epithelial cells have in common:
How is the bacteria cell structurally different from both the amoeba and the epithelial cell?
Describe the difference in shape between the amoeba cell and the human epithelial cell.
6. Did you see a stained nucleus in: (Highlight/Underline yes or no)
a) Bacteria: YES NO
b) Onion Root: YES NO
c) Human Red Blood Cells: YES NO
d) Human White Blood Cells: YES NO
e) Human Epithelial Cells: YES NO
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