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Apr 3, 2024

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Microscopy Worksheet 5 50 pts Background One of the most common instruments used in biology is the microscope. The invention of the microscope revolutionized biology. It helped establish that living things are made of cells and that microorganisms exist that are invisible to the naked eye. Microscopes are valuable tools in biology because they are capable of increasing both the magnification and resolution of the observed specimen. Magnification refers to the apparent size of the specimen, whereas resolution refers to the clarity of seeing two objects as distinctly separate. The magnification power of a compound light microscope is determined by its ocular and the objective, which is why we refer to the microscope as a compound light microscope . A typical ocular has a magnification power of ten (10X). The objectives are magnifying lenses fastened on the rotating nosepiece. The objectives on student microscopes are 4X, 10X, 40X, and sometimes 100X (for oil immersion). To calculate the total magnification of the specimen, one would multiply the ocular power by the objective power as below: Total magnification = magnification of ocular X magnification of objective used We will be introducing a compound light microscope by first acquainting you with the parts and functions of the parts of the microscope and then by viewing a variety of cell specimens. Eukaryotic cells are those that contain a nucleus and membrane-bound organelles. Prokaryotic cells , or bacterial cells, are much smaller in size and do not contain a nucleus or membrane-bound organelles. MICROSCOPE FIELD OF VIEW When you look into a microscope that has the power turned on, you should see a bright circle. This bright circle of light shows you the area of the slide that is being magnified and is called the field of view . As you increase objective magnification power, the field of view gets smaller. This does not mean the bright circle that you see through the microscope becomes smaller. It simply means a smaller area of the slide is being magnified.
Diameter of the field of view for the student light microscope. Objective Lens Diameter of the Field of View (1 mm = 1,000 μm) 4X 4.5 mm or 4,500 μm 10X 1.8 mm or 1,800 μm 40X 0.5 mm or 500 μm One can use the diameter of the field of view to estimate the size of the object that is being observed under the microscope. To estimate the size of the object observed, use the following steps: 1. Select a suitable magnification for size estimation. It is important that you choose a magnification that allows you to observe the entire object. If the object is very small, use the highest magnification available for your estimation. 2. Place the object in the center of the field of view. Estimate the number of objects that can fit across the diameter of the field of view. 3. Estimated object size = Diameter of the chosen field of view ÷ Estimated number of object across the diameter of the field of view. Virtual Labs I. Operation of bright field microscope 1. (2 pts) What is the difference between resolution and contrast? Resolution is the ability to distinguish fine detail, while contrast is the ability to recognize objects such as cells from a background. 2. (1pt) What is the field of view? The field of view is the amount of the slide you are able to see through the microscope’s eyepiece. 3. (1pt) What is the relationship between objective, magnification power and the field of view? As magnification in the microscope increases, the field of view decreases. 4. (1pt) Total magnification = Objective lens multiplied times the 10x of the ocular lens (Is the overall enlargement of the image of a specimen.)
5. (1pt) What is the total magnification of the observed objects in a microscope that is using the 40X objective lens? The total magnification of the observed objects in a microscope that is using the 40x objective lens would be 400x. 6. (1pt) When using the 100X objective lens, a drop of immersion oil is needed on the specimen slide. 7. (1pt) How does changing light intensity affect the contrast of an image in a microscope? When the light intensity is to bright it can blind the view, so you only see white, and if it is to low, you will not be able to see anything, so it is important to adjust the light in a way where you can see every detail of the specimen. 8. (1pt) How do you bring a specimen into focus quickly? To bring a specimen into focus quickly is better to start with a 4x objective lens and adjust the focus with the fine adjustment knob, and after that increase the objective lenses. II. Label the Parts and Describe the Function of the Parts of the Microscope Directions: With the help from the last activity, and your computer, label the parts of the microscope, listed below, and describe the function of the part next to your label. (10 pts) 1. Mechanical Stage: where you place a specimen for viewing. 6. Rotating Nosepiece: houses and moves all the objective lenses. 2. Fine Focus Knob: moves the stage up and down slowly to sharpen the image of the specimen. 7. Objective lens: closest lens to the specimen. Magnify the image of the specimen. 3. Coarse Focus Knob: focus the image under low power magnification, move the stage up and down rapidly. 8. Oculars: adjustable piece to place the eyes to look at the specimens. 4. Condenser: lenses used to collect and focus light from the light source into the specimen. 9. Stage adjustment knobs: moves the stage mechanically (left,right,forwardand backward). 5. Iris Diaphragm: controls the amount of light that reaches the specimen. 10. Light source: reflects the light from an external source to the sample.
II. Microscopy – Plant Cells (Onion Epidermal Cells) Background All living systems are made up of either prokaryotic or eukaryotic cells. Bacteria are prokaryotic organisms. Prokaryotic cells are generally smaller, less complex, and most importantly, the genetic material (DNA) is not enclosed in a membrane-bound structure (known as the nucleus). All bacteria are prokaryotes. Eukaryotic cells make up all the other kingdoms of life: plants, animals, fungi, and protists. Eukaryotic cells are generally larger, more complex in cellular organization, and have distinct membrane- bound structures known as organelles (including having a nucleus). Most cellular structures are too small and colorless to be visually identifiable using a light microscope. However, it is possible to visualize nuclei in eukaryotic cells using a light microscope. In this next simulation, you will observe onion epidermal cells, which are harvested from the inner portion of a layer from an onion bulb. The bulb of the onion grows underground so, therefore, the organelle which accomplishes photosynthesis, the chloroplast , will not be visible in an onion bulb. Furthermore, since
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