Biology > Lab Report > BIO 103 Module 4 INTRODUCTION TO THE LIGHT MICROSCOPE AND CELLS VIRTUAL SCOPE Lab Multiline-1-1. Lab (All)

BIO 103 Module 4 INTRODUCTION TO THE LIGHT MICROSCOPE AND CELLS VIRTUAL SCOPE Lab Multiline-1-1. Lab 4: INTRODUCTION TO THE COMPOUND LIGHT MICROSCOPE AND VIEWING CELLS.

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Page | 1 Lab 4: INTRODUCTION TO THE COMPOUND LIGHT MICROSCOPE AND VIEWING CELLS Introduction, Part 1: Parts of the Compound Light Microscope The compound microscope is a precision instrument. Treat... it with respect. When carrying it, always use two hands, one on the base and one on the neck. The microscope consists of a stand (base + neck), on which is mounted the stage (for holding microscope slides) and lenses. The lens that you look through is the ocular (paired in binocular scopes); the lens that focuses on the specimen is the objective. Your microscope has four objectives of varying magnifications (4x, 10x, 40x, and 100x) mounted on a revolving nosepiece. The 100x objective is a special oil immersion objective that needs to be used with oil. Positioning the specimen requires that you turn the mechanical stage controls, which operate the slide bracket on the surface of the stage. One control moves the specimen in the x-direction, and the other moves the specimen in the y-direction. Focusing on the specimen is achieved by knobs that move the stage up and down, so that it is closer or farther from the objective. There are two knobs, an outer coarse focus and an inner fine focus. The substage condenser directs light through the slide into the objective. An iris diaphragm on the substage condenser controls the amount of light reaching the objective, and also affects the contrast of the specimen. Review the diagram below to familiarize yourself with the microscope parts. Parts of the Microscope 1. Ocular lens 2. Revolving nosepiece 3. Objective lens 4. Stage adjustment knobs 5. Coarse focus knob 6. Fine focus knob 7. Light source 8. Light switch 9. Light intensity dial 10. Iris diaphragm lever (located on the substage condenser) 11. Stage 12. Stage clip Page | 2 Introduction, Part 2: Magnification The compound microscope has two sets of lenses; the ocular lens (or eye piece) which magnifies an object 10 times its normal size, and the objective lenses located on a revolving nosepiece. Rotate the nosepiece and notice how each objective lens clicks into place. Each objective lens has a different magnification of power written on it (such as 4, 10, 40, or 100). This number is the power of magnification for each of the objective lenses. For total magnification multiply the ocular power (10x) times the objective lens that is in place. For example, if you have a 10x ocular and a 10x objective, the total magnification is: 10x × 10x = 100x. Introduction, Part 3: Using the Compound Light Microscope Getting a Focused Image Adjust the interocular distance (distance between the oculars) by gently pressing the oculars together or pulling them apart until you see a single circular field of view. Optimizing Resolution and Contrast Resolution is the ability to distinguish two closely spaced points on your specimen, and it is always best with the iris diaphragm wide open. Contrast is the magnitude of difference between light and dark objects, and it increases as you close the aperture of the iris diaphragm. Getting the best image, then, requires that you find the right balance. Slowly open and close the iris diaphragm to get a feeling for the effect this has on your image. Changing Magnification Always start with the scanning objective (4x) to get oriented and locate an area of interest, and then switch to low power to examine interesting regions more closely. To change magnification, simply rotate the nosepiece to bring one of the other objectives into the light path. Always center the area of interest in your field of view before moving to the next higher power. Finishing Up To put your microscope away properly, perform the following in this order: Turn down the illumination; turn off the power; switch back to the 4X objective; remove your slide; unplug the power cord and wrap it around the base of the scope; lower the stage to hold the cord in place. Procedure Activity 1: Getting to Know the Virtual Compound Light Microscope: To complete your lab report, you must access the Virtual Microscope online. Once there, work through the tutorial titled Getting Started by clicking Start Tour. Make sure you explore all the microscope parts and learn their names and functions. Supplement your exploration of the virtual microscope with this video explanation of how the virtual microscope works. Now you are ready to test your knowledge. Click here for a vocabulary workout and here for a visual workout on the parts of the compound light microscope. Page | 3 Testing Your Knowledge: Complete the following 1. Match the following microscope parts with the letterthat represents them on the diagram of the microscope. Ocular Coarse focus Fine focus Stage adjustment 2. Use what you learned in the tutorial and in the portion of the lab titled Part 2: Magnification to fill in the following table. Ocular Magnification Objective Magnification Total Magnification 3. When first viewing a specimen, always begin at the objective to get oriented and locate an area of interest. 4. Coarse focus is only ever used with the objective. 5. Describe the function(s) of the iris diaphragm lever. Activity 2: Viewing the Letter “e” The first slide you will examine is a slide of a type-set letter “e” (top right). We begin with this familiar example instead of a more exciting one so that you can concentrate on your microscope technique. We will be looking at much more interesting things later. Follow the tutorial and refer back to the Introduction: Using the Compound Light Microscope portion of this lab to properly center and focus the "e" on each of the objectives. Page | 4 1. On paper, sketch the "e" exactly as it appears at each of the following objectives. Sign and date your 2. While looking through the microscope, use the stage adjustment knobs to move the slide to the left. a. What direction does the image of the letter “e” appear to move? b. Now, move the slide to the right. Which way does the image appear to move? c. Move the slide away and towards you. Describe the resulting direction of movement for the image. Activity 3: Viewing Plant Cells – Domain Eukarya, Kingdom Plantae 1. Go to the virtual microscope and bring the onion root tip slide into focus at the 4x, 10x, and 40x Page | 5 2. At 40x and even 10x, the onion cells appear grainy (pixelated) using the virtual microscope. This is not the case when using a good compound light microscope in a lab. To get a better feel for what different plant cells look like at different magnifications, view the following and answer the questions associated with them. a. This micrograph of onion root tip cells at 400x is a bit clearer than that seen through the virtual microscope. We will be looking at onion root tip cells again when we study cell reproduction. Notice the boxy nature of plant cell units. These are the cell walls. What do you think the dark area in the center of each of the rectangles is? b. Now view a plant specimen containing the organelles of photosynthesis. View the video. After watching the video, identify the green circular organelles at the end of the red leader lines and the plant cell structure enclosed by the black rectangular outline in the followingmicrograph. circular organelles = black outline = Activity 4: Viewing Animal Cells: Domain Eukarya, Kingdom Animalia 3. Now use your virtual microscope to view the human cheek smear slide. Cells on this slide are epithelial cells taken from the inside of your mouth by scraping a toothpick on the inside of your cheek. Bring the cheek cells slide into focus at the 4x, 10x, and 40x objectives. Make a general sketch of what you see at each of the magnifications. Label the nucleus and plasma membrane of one cell on the 400x sketch. Sign, date, photograph, and insert as before. [Show More]

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