LAB ACTIVITY: USING A MICROSCOPE

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1 Name: Date: Period: Lab Partner(s): LAB ACTIVITY: USING A MICROSCOPE Objectives: Demonstrate the proper use and care of a compound light microscope and stereomicroscope. Focus the compound light microscope at low power, medium and high power. Make a wet-mount slide to examine under the microscope. Compare the movement of the images seen through a compound light microscope and a stereomicroscope Materials: Compound light microscope, stereomicroscope, water, forceps, lens paper, glass microscope slide, coverslip, pipette, scissors, paper towel, newspaper, small plants, pipette, moss, leaves Purpose/Question: The purpose of the lab is to train you to use of a compound light microscope and a stereomicroscope. You will answer the questions: How does the type of microscope affect the detail and movement of images under the microscope? How does the magnification affect the focus and resolution of a compound light microscope? Background: In almost every type of biological research, the microscope plays a fundamental role. Biologists use it to study cells and tissues, which are too small to be seen with the unaided eye. The microscope used most often is the light microscope, which uses light to form an enlarged image of a specimen. The two types of light microscopes are the compound light microscope and the stereomicroscope. Compound light microscopes are used to view tiny living organisms and preserved cells mounted on glass and covered with a coverslip. Under the compound light microscope, most objects and microorganisms are observed in a drop of water. A slide that is prepared with water is called a wet mount. Stereomicroscopes are used to study larger specimens and provide a three-dimensional view of the specimen s surface and will not utilize wet mounts. Pre-lab Drawing Assignment: Read Activity 1.1 and 1.2 in your textbook (pages 13-14) to familiarize yourself with how to make biological drawings. Choose a living thing you can view at home (plant, animal, protist, etc.) and make a biological drawing below. Label four keys features and calculate the magnification of your drawing.

2 Microscope Part Ocular lens Eyepiece (magnification x) Body Tube Function Arm Stage Coarse adjustment Fine adjustment Lamp (light source) Revolving nosepiece Low-power objective (magnification x) Medium-power objective (magnification x) High-power objective (magnification x) Diaphragm Base

3 Carrying the Microscope: In order to move a light microscope you wrap one hand around the arm of the microscope and use the other hand to support the base. Never carry the microscope with one hand. The arm of the microscope connects the magnification pieces to the stage and to the light source. Tips to using microscopes: The object you are looking at must be transparent (light can pass through). Always place the specimen on a slide with a coverslip to hold the specimen in place and to protect the lens of the microscope. The slide is placed on the stage of the microscope and held in place with the stage clips. Once the slide is secured in place you can move the revolving nose piece to low power magnification. Always start on low power so we can easily locate the object; under low power we can see less detail but more of the object (the field of view is much larger). Use the coarse adjustment (large knob) to bring the image into focus. Once the object is in focus using the coarse adjustment (moves the stage up and down) move the revolving nosepiece to the next magnification. Use the coarse adjustment and then the fine adjustment (moves the stage up and down but in very small increments) to focus the image. Center the image before moving to another power using the knobs next to the stage. After focusing the object under medium power you can then move the revolving nosepiece to high power and focus on the object. In high power you will be able to see the most detail but your field of view will be smallest. To change the amount of light shining on the object, adjust the diaphragm underneath the stage. LAB DIRECTIONS Part 1: 1. Complete the functions of each microscope part in the table above. 2. Carry a microscope to your lab table as shown by your teacher. Note: A microscope is expensive and fragile. It is important to use it correctly to avoid damaging it and avoid breaking slides or destroying specimens. When you use a microscope be sure it rests securely on your lab table away from the edge. 3. Locate each microscope part listed in the data table and shown in the diagram on the previous page. To calculate the magnification for each power of the revolving nosepieces, multiply the eye piece magnification by the revolving nosepiece magnification. 4. Lower the stage as far as possible by turning the coarse adjustment knob toward you. Turn the lowpower objective into position over the stage. 5. Obtain a prepared slide from your teacher and place secure it to the stage using the stage clips. 6. While observing the stages from eye level, use the coarse-adjustment knob to position the objective as close to the slide as it will go without touching the slide. 7. Look through the eyepiece. Always keep both eyes open as you look into the eyepiece. Keeping both eyes open avoids eye strain. If the lens is dirty, ask your teacher to demonstrate the correct way to clean it. Note: Never us anything other than lens paper to clean the lenses of the microscope. 8. Focus with the coarse-adjustment knob by turning it away from you. Note: Never focus objectives downward. You may run the objective into the slide and break the slide or damage the objective. 9. Complete focusing by slowly turning the fine-adjustment knob back and forth. When the object you are viewing is in focus and exactly in the middle of your field of vision, switch to high power. Note: never use the coarse adjustment knob at high power.

4 a. Draw what you see under 100X & 400X Name of slide: 100X Name of slide: 400X b. Do these cells belong to a unicellular or multicellular organism? c. Are the cells prokaryotic or eukaryotic? How do you know? d. What parts of the cell can you see at this magnification? Part 2: MAKING A WET MOUNT 10. Use scissors to cut out a small lowercase e from a piece of newspaper. Note: Do not use one from a headline. 11. With a medicine dropper, place one drop of water in the middle of a clean glass microscope slide. With forceps, place the letter e in the drop of water as seen in the diagram. 12. Hold a coverslip at a 45 O angle to the slide at the edge of the drop of water as seen in the diagram. Lower the coverslip slowly to avoid forming air bubbles. Under the microscope, air bubbles look round and have dark edges. DO NOT PRESS DOWN ON THE COVERSLIP! 13. Place your wet mount on the microscope stage with the letter facing you as if you are reading it. Using the low-power objective, center and focus the microscope on the letter. Then switch to high power. a. Draw what you see under 100x & 400X 100X 400X

5 b. Describe how the letter g would look if placed under the microscope. c. What happens to the amount of detail you can see in the letter as you go from low to high power? 14. As you look through the eyepiece, have your partner adjust the diaphragm below the stage. a. What happens as you adjust the diaphragm? 15. As you look into the microscope, have your partner use the knobs on the side of the stage to move the slide to the right and then to the left. a. What happens to the image as the slide moves to the right (which direction does the image move)? b. What happens to the image as the slide moves to the left (which direction does the image move)? c. Have your partner move the slide away from you, which direction does the image move? STEREOMICROSCOPE 16. Choose one of the objects collected by your teacher. Place the object under the stereomicroscope and focus using the adjustment knobs. a. Draw the object in the space to the right. b. Move the object to the left. In which direction did the object move? 17. Make a wet mount using a small piece of the object you chose for the stereomicroscope and observe it under low power with the compound light microscope. a. Draw the object on high power to the right. b. Are you able to see all of the object under the compound light microscope? c. Why do the objects look different under the stereomicroscope?

6 ANALYSIS QUESTIONS 18. Under which power do you see the largest amount of the specimen? 19. If a microscope has an ocular lens with a 5x power, and has objectives with powers of 10x, 20 and 50x, what is the total magnification when using each objective lens? 20. When using a microscope, what steps do you take to focus on the specimen? 21. Why do you need a coverslip when making a wet mount? 22. Why should you always begin to use a microscope with the low-power objective? 23. Why must the specimen be centered before switching to high power? 24. Which type of microscope would you use to view each of the following (compound or stereo) a. Spider b. Blood cell c. Bacteria d. Tree bark 25. List two differences and two similarities between the stereomicroscope and light microscope. Use the table below. Compound Light Microscope Both (Similarities) Stereomicroscope