Introduction to the Light Microscope

Transcription

1 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 maybe 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 Procedure: Parts of the Microscope Coverslip Eyedropper Newspaper Scissors Beaker Threads Colored pencils 1. Use a piece of lens paper to carefully clean all of the ocular and objective lenses. This will remove any dust or other debris that may be present on the lenses. 2. Examine your microscope. Familiarize yourself with the parts of the microscope. PLEASE DO NOT USE THE OIL IMMERSION OBJECIVE!!!! a. The magnification written on the ocular lens (eyepiece) is 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 3. The total magnification using the lenses can be determined by multiplying the magnifying power of the objective lens with the power of the ocular lens. What is the total magnification of an item viewed with the: a. SCANNING objective x Ocular lens = b. LOW power objective x Ocular lens = c. HIGH power objective x Ocular lens = - 1 -

2 4. Examine the underside of the stage. If present, locate the diaphragm (it has a lever). Your teacher may have one of these pieces that you can look at. What is the function of the diaphragm? 5. Find the dial on the base of the microscope. The numbers on the edge of it range from ONE to. What happens when you turn the dial? 6. Look into the eyepiece and twist it left and right. Notice the line inside that moves as you twist. (Some microscopes do not have this, see if you can find one that does in the room). What do you think this is for? Making a Wet Mount of the letter e 7. 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. a. Place the e right side up on the slide. Add 2 or 3 drops of water on top of the e with an eyedropper. b. Gently lower the coverslip, beginning at one edge, over the water and e. Avoid getting air bubbles under the coverslip. c. Place the slide of the "letter e" on the stage so that the letter is over the hole and is right side up. d. Use the scanning objective to view the letter and use the coarse knob to focus. e. Switch to low power by rotating the nosepiece. f. Repeat on high power. Remember at this point, you should only use the FINE adjustment knob. g. 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?) h. Have your partner push the slide to the left while you view it through the lens. i. Which direction does the e appear to move? - 2 -

3 Depth Perception 8. Obtain a slide with 3 different colored threads on it. a. First, view the slide under scanning and low power. You should note that while you focus on one color of thread. The other threads become fuzzy. The microscope can only focus on one area at a time. b. Figure out which thread is on top by lowering your stage all the way, then slowly raising it until the thread comes into focus. The first thread to come into focus is the one on top. i. Which color thread is on top? ii. Which color thread is in the middle? iii. Which color thread is on the bottom? 9. Sketch & color what you see on the slide (scanning). Using nice, straight lines label the top, middle, and lower thread colors. Then, be sure to give the total magnification using the scanning objective. 10. Choose 2 specimens from the box of "common things". Use the circles below to sketch your specimens under SCANNING and LOW power. You may practice focusing with the high power, but you do not need to sketch it

4 11. Label each specimen using the name written on the slide. Then, be sure to give the total magnification using the required objectives. Specimen #1 Specimen #2-4 -

5 12. Answer true or false to each of the statements. 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