Compound Microscope Lab Microscope Parts and Appropriate Use Exercise

Transcription

1 Name Date Period Compound Microscope Lab Microscope Parts and Appropriate Use Exercise Objective: The purpose of this lab is to learn how to use a Compound Microscope, make a wet-mount slide and understand how these skills and equipment can help further the study of biology. (Indiana State Academic Standards: Biology, 4.1, 5.1, & 5.2) Instructions: Follow each step of the procedure below. This lab is to be completed in your LAB JOURNAL. Materials: Microscope Scissors Prepared slide Forceps or pin Microscope slide Water Coverslip Eyedropper Newspaper Procedure: PART I: The Anatomy of a Microscope 1. Remove microscope from its storage area by placing one hand beneath the base and grasping the arm of the microscope with the other hand. BE CAREFUL! 2. Gently place microscope on lab table with the arm facing you. Microscope s base should rest evenly on and away from edge of the table. 3. Using the following descriptions, identify the parts of the microscope. a. Label microscope diagram on DIAGRAM 1. Begin at the top of the microscope. i. Eyepiece: lens where your eye looks to see an object magnified; the eyepiece has a lens which, by itself, magnifies 10 times (10X) to make the object look 10X its actual size ii. The eyepiece is the topmost end of the body tube. The body tube is responsible for putting the correct amount of distance between the eyepiece lens and the lenses at the bottom of the body tube. iii. Look at the bottom of the body tube. You should see a round circle attached which moves when you turn it. Go ahead and turn the round revolving nosepiece. Notice that there are three more lenses attached to the revolving nosepiece each with a different magnifying power. The function of the revolving nosepiece is to place a lens in the down position to help the microscope. As you turn the revolving nosepiece, listen and feel for a click. The new lens is in place when you hear the click. iv. Look at the three lenses on the revolving nosepiece. Notice that they are three different sizes. These three lenses are called objective lenses. Their function is to increase the magnification of the microscope. 1. The shortest is called the scanning power objective when used alone, its magnification is 4X. Look on the side of the lens. You should see the number 4 printed there. 2. The next lens is called the low power objective when used alone, its magnification is 10X. Look on the side of the lens. You should see the number 10 printed there. 3. The third, or longest lens, is called the high power objective when used alone, its magnification is 40X. Look on the side of the lens. You should see the number 40 printed there. Part I (a): Calculating Total Magnification Since this is a compound microscope, the objective lenses and eyepiece lenses are not used by themselves; instead, two lenses are used together. To determine the total magnification of the microscope with the scanning power objective in the locked, down position, multiply the magnification number of the eyepiece lens times the number of the scanning power objective lens. Total magnification = eyepiece magnification X objective lens magnification So the microscope, when using the scanning power objective lens in place, has a total magnification of 40X. Using the formula shown above, Complete Table 1. 40X = 10X X 4X

2 Locate the stage of the microscope. The stage holds the slide being observed. Attached to the stage are two silver-colored stage clips. These are used to hold the slide in position. In the stage there is an opening. This opening allows light from the lamp under the stage to shine through an object. Remember, a light microscope depends on light being able to go through an object. Now look under the stage. You should find a disk with holes in it. Notice that the holes are of varying sizes. This is called the diaphragm and works like the iris of your eye. As the hole in the diaphragm gets larger, more light can go through the opening on the stage and thus through the object you are looking at. Plug in the cord and check the position of the cord to make sure it is out of the way. Turn on the lamp to be sure it is working. Turn the diaphragm to see how less light goes through the opening on the stage when the smaller hole is lined up and more light goes through when the larger holes are lined up. Turn the microscope off at this time. 9. On the sides of the microscope are two knobs used to focus the lenses. The larger knob is called the coarse adjustment knob. It is used to get an object into as close focus as possible BUT THIS KNOB MAY ONLY BE USED WHEN YOU ARE USING THE SCANNING OR THE LOW-POWERED OBJECTIVES. 10. The smaller knob is called the fine adjustment knob. This knob is for fine tuning the focus. It may be used with any objective lens clicked into place. PART II: Making A Wet-Mount Slide Obtain a SLIDE, a COVERSLIP, the letter e from a piece of newsprint. (It should look just like this e and be about this size), and some water. Cut a small letter e from the newspaper and place it onto the slide. To make a wet-mount slide, use the eyedropper to place water over the letter e. Take a small coverslip (about 2cm x 2cm) at a 45 o and place one edge of the coverslip at the edge of the water. Using a pin or a forceps, lower the coverslip over the letter e and the drop of water. Try not to trap any air bubbles under the coverslip since these will interfere with your view of the object. Congratulations, now you have a wet-mount slide! *As the water evaporates while you look at the slide, you may need to add water to keep the slide fresh. This is done by placing the tip of the eyedropper next to the edge of the coverslip and adding a drop of water. The water will run underneath the coverslip. Be sure the stage is as far from the objective lenses as possible. You do this by turning the coarse adjustment knob. Be sure you have the scanning power objective (the shortest one) clicked in the down position. Clip the slide with the letter e into place on the stage of your microscope and position it so that the letter is directly over the center of the stage opening. PLACE THE SLIDE WITH THE LETTER e POSITIONED AS IF YOU WERE READING IT. HUMOR ME AND DO IT THIS WAY I REALLY DO HAVE A REASON FOR THIS! EVEN IF YOU HAVE TO PLACE YOUR SLIDE AT AN ANGLE, HAVE THE LETTER e FACING YOU AS YOU LOOK AT THE MICROSCOPE STAGE Turn on the microscope lamp. Using the coarse adjustment knob, raise the stage as far as it will go without bumping into the objective lens. Look through the eyepiece lens. While looking through the lens, use the coarse adjustment knob to lower the stage until the letter e comes into view. Focus it as well as you can with the coarse adjustment knob and then use the fine adjustment knob for fine-tuning. KEEP YOUR HANDS OFF THE SLIDE UNLESS YOU ARE CENTERING IT IN THE FIELD OF VISION! (The large, lighted circle you see is called the field of vision.) You should see the letter e. What is wrong with it??? If you said it was upside down, you are exactly right! As the light passes through the lenses, it is bent. This causes you to the e upside-down and backwards. Draw the letter e on Diagram 2-A exactly as you see it through the eyepiece.

3 9. While looking through the eyepiece at the letter e, move the slide to your right. Notice the direction that the letter appears to move. Record the direction that the letter moves in the analysis section of your lab journal. 10. Now move the slide to the left. Note the direction that the letter appears to move. Record your observations in the analysis section of your lab journal. 11. Re-center the letter e. Now move the slide up and away from you. 12. Re-center the letter e. Now move it down. 13. To switch the objective lens, first re-center the letter e in the field of vision. Look at the slide on the stage and rotate the revolving nosepiece until the low power objective clicks into place. Use the low power objective lens to observe the letter e. Use the coarse and fine adjustment knobs to get the letter into focus. 14. Draw the letter e on Diagram 2-B exactly as you see it through the eyepiece. 15. Before you change the objective lens to high power, make sure there is some ink in the center of the field of vision. The field narrows so much that, if there is no ink, you may miss the letter completely when you try to see it on high power. 16. DO NOT TOUCH THE COARSE ADJUSTMENT KNOB OR THE FINE ADJUSTMENT KNOB AGAIN UNTIL YOU ARE TOLD TO DO SO!!!!!!! 17. Turn the revolving nosepiece while looking at the stage. When you go to the high power objective you need to turn the nosepiece while looking at it to be sure it will clear the slide without hitting it. For this slide IT WILL BE FINE IT WILL NOT HIT THE SLIDE EVEN THOUGH IT SEEMS IT MIGHT. Turn the revolving nosepiece until the high power objective clicks into place. 18. USE ONLY THE FINE ADJUSTMENT KNOB WHEN YOU ARE ON HIGH POWER!!! The coarse adjustment knob has been known to smash right through a slide. NEVER USE THE COARSEADJUSTMENT KNOB WHEN ON HIGH POWER. Focus the slide as well as possible it may not get into focus very clearly. 19. In the circle on Diagram 2-C, draw a picture of the letter e as you now see it. 20. You may have noticed that when you changed the magnification by changing the objective lenses, the image was only slightly out of focus if at all. This is because modern microscopes are PARFOCAL. This means the microscope will hold its focus when the objective lenses are changed. 21. To put the microscope away properly, turn it off, unplug, return the objective lenses to the scanning lens, wrap the cord, and carry it to its cubby using the arm and the base.

4 Cut along the dotted line and paste the following sections in your lab journal as described in the lab journal format. MATCHING (Diagram 1-A) Match the structure with its function: 1. Eyepiece 2. Arm 3. Stage 4. Opening of the stage 5. Fine adjustment knob 6. Coarse Adjustment knob 7. Base 8. Lamp 9. Diaphragm 10. Stage clips 11. Low power objective lens 12. High power objective lens 13. Scanning power objective lens 14. Revolving nosepiece 15. Body tube A. Holds the slide in place B. Moves the stage up and down for focusing C. Provides a magnification of 10X and is the middle sized of the objectives D. Maintains a proper distance between the eyepiece and the objective lenses E. Contains a 10X lens; where you place your eye F. Supports the microscope G. Contains the objective lenses and moves them into position for use H. Supports the body tube and is held to carry the microscope I. Produces light to shine up through the body tube J. Provides a magnification of 40X for a total magnification of 400X K. Supports the slide being observed L. Regulates the amount of light going through the opening in the stage and into the body tube M. Allows the microscope to be in sharper focus N. A hole which allows light through the stage and to the object and the body tube. O..Provides a magnification of 4X for a total magnification of 40X DIAGRAM 2 (Letter e drawings from steps 8, 14 & 19) 2-A 2-B 2-C Magnification Magnification Magnification Scanning Power Low Power High Power

5 DIAGRAM 1-B Table 1 SCANNING POWER LOW POWER HIGH POWER EYEPIECE OBJECTIVE TOTAL MAGNIFICATION 10X 10X 10X

6 Analysis Questions Answer the questions below using complete sentences in your lab journal. 1. What is meant by field of vision? 2. How does changing the magnification change your field of vision? 3. Describe how to make a wet-mount slide. 4. Why must you be careful when focusing when you are using the high power objective? What precautions should you take? 5. When you moved the e to the right in Part II step 9, which direction did it appear to move? 6. In Part II step 10 when you moved the e to the left, which direction did it appear to move? 7. In Part II steps 11 & 12 what did you notice about the direction the e appeared to move when you moved the slide up and down? 8. If a stationary object (like the letter e ) was moved to the upper right corner of the field of vision as you looked through the microscope and you wanted to get it into the center, in which 2 directions would you have to move the slide? You would have to move it to the 9. If you were tracking a microorganism that appeared to be moving from the right side of the field of vision to the left side of the field of vision, which way would you move the slide to keep it in view? Why? and Lab Journal Format Title Objective Materials Slide Forceps Matching Diagram 1-A Microscope Diagram Table 1 Diagram 1-B Letter e Wet Mount Diagram 2 Analysis Questions: #1-9