Anatomy: Introduction to the Light Microscope Background: Microscopes are very important tools in biology. The term microscope can be translated as to view the tiny, because microscopes are used to study things that are too small to be easily observed by other methods. The type of microscope that we will be using in this lab is a compound light microscope. Light microscopes magnify the image of the specimen using light and lenses. The term compound means that this microscope passes light through the specimen and then through two lenses. The lens closest to the specimen is called the objective, while the lens nearest to the user s eye is called the ocular lens or eyepiece. When you use a compound light microscope, the specimen being studied may be either a prepared slide that is permanent and purchased from a supply company, or it may be a wet mount that is made for temporary use and is made in the lab room. Objective: Write two (2) objectives you should accomplish by carrying out this lab activity. Materials: Microscope Lens paper Slide Coverslip Eyedropper Newspaper Scissors Elodea Cheek cells Toothpicks Methylene blue Petri dish Colored pencils Ruler Procedure: 1. Examine your microscope. Familiarize yourself with the parts of the microscope. a. The magnification written on the ocular lens (eyepiece) is x. b. The magnification written on: i. the scanning objective (this is the shortest objective lens) x ii. the low power objective is x iii. the high power objective is x iv. If you have a 4 th lens, it is an oil immersion lens. DO NOT USE IT! 2. The total magnification using the lenses can be determined by multiplying the objective lens with the ocular lens. What is the total magnification of an item viewed with the: a. SCANNING objective. b. LOW power objective. c. HIGH power objective. 3. Examine the diaphragm (underneath the stage). Move the lever to the left and right. What does the diaphragm do? 4. Look at the dial on the base of the microscope. The numbers on the edge of it range from ONE to. - 1 -
5. Look into the eyepiece and twist it left and right. Is there a line inside that moves as you twist? Some microscopes do not have this, but if it did, what do you think it would be used for? 6. Use a piece of lens paper to carefully clean the ocular and objective lenses. This will remove any dust or other debris that may be present on the lenses. Measuring the Field of View 7. Place a transparent, plastic ruler on the stage of the microscope and look at it using the scanning, low and high power objectives. 8. Record how many millimeter marks you can see from one side to the other while passing through the center of your field of vision. Be sure to estimate any pieces of the ruler leftover from the mm marks. a. Scanning mm b. Low mm c. High mm Make a wet mount of the letter e. 1. Cut out a lowercase e from a piece of newspaper. Make sure that the e is taken from the normal print of an article; otherwise it may be too big or too small for proper viewing. 2. Place the e right side up on the slide. Add 2 or 3 drops of water on top of the e with an eyedropper. 3. Gently lower the coverslip, beginning at one edge, over the water and e. Avoid getting air bubbles under the cover slip. 4. Place the slide of the "letter e" on the stage so that the letter is over the hole and is right side up. 5. Use the scanning objective to view the letter and use the coarse knob to focus. 6. Switch to low power by rotating the nosepiece. 7. Repeat on high power. Remember at this point, you should only use the FINE adjustment knob. 8. Draw the "e" as it appears at each magnification. Drawings should be drawn to scale and you should note the orientation of the e in the viewing field (is it upside down or right side up?) - 2 -
9. Have your partner push the slide to the left while you view it through the lens. Which direction does the e appear to move? Elodea Cells Making a Wet Mount 1. Obtain a leaf from the aquatic elodea plant provided by your teacher. 2. Follow the wet mount procedures outlined in class, prepare a slide for viewing. 3. View the slide under scanning and low power and draw five (5) cells. Then view the slide under high power. Draw what you see. Label the cell wall, cytoplasm, chloroplasts and nucleus. Cheek Cells Staining a Slide 4. Place a drop of methylene blue stain in the center of a clean slide. 5. Using a toothpick, gently scrape the inside of your cheek to collect some cells. 6. Carefully transfer these cells to the glass slide by stirring the end of the toothpick in the stain. Throw the toothpick away in the trash. 7. Place a cover slip on the slide. Avoid creating air bubbles. - 3 -
8. Locate the small cells using the scanning objective. They will be too small to see well. 9. Switch to low power and look for clear, purplish blobs. If you are looking at something dark purple, it probably isn t a cheek cell! 10. Find a cell, bring it into focus and then center it in your field of vision. 11. Now, switch to high power and bring into sharp focus. (YOU NO LONGER MAY USE COARSE ADJUSTMENT! ONLY FINE!!!) 12. Draw the cheek cells under low and high magnification. Label the cell membrane, cytoplasm and nucleus of a cheek cell in high power. Low ( X) High ( X) 13. Why is methylene blue necessary? 14. Cheek cells do not move on their own, so you will not find two organelles that function for cell movement. Name these organelles. 15. The light microscope used in the lab is not powerful enough to view other organelles in the cheek cell. Why not? 16. List 2 organelles that were NOT visible but should have been in the cheek cell. - 4 -
17. True or False? Write T for true or if false, write the correct word(s) to replace what s in italics. a. On high power, you should use the coarse adjustment knob. b. The diaphragm determines how much light shines on the specimen. c. Magnification using the low power objective is greater than the power of the scanning objective. d. The fine focus knob moves the stage up and down. e. Images viewed in the microscope will appear upside down. f. If a slide is thick, only parts of the specimen may come into focus. g. The type of microscope you are using is a scanning microscope. h. For viewing, microscope slides should be placed on the objective. i. To switch from low to high power, you must rotate the revolving nosepiece. j. Total magnification is determined by adding the powers of the ocular and the objective lenses. - 5 -