Use of the Light Microscope

Objective: To become familiar the how the compound light microscope works. Materials: microscope slides coverslip dropper water hair letter “e” potato scrapings iodine dark thread light thread Procedure: Part A: Understanding the power of the microscope 1. Look at the eyepiece Q#1 What is the magnification of the ocular lens in the eyepiece? 2. Look at the three objectives a. The objective with the green line is the low power objective. Q#2 What is the magnification of the low power objective? b. The objective with the yellow line is the high power objective. Q#3 What is the magnification of the high power objective? Q#4 What is the total magnification under low power? Q#5 What is the total magnification under high power? (Remember total magnification includes both the eye piece X the objective)

Part B: Position of objects when viewed with a microscope 1. Prepare a wet mount by adding 1-2 drops of water to a slide. 2. Place the lowercase “e” on the slide. 3. Place the coverslip over the “e”. 4. Place the slide on the microscope stage so that the letter “e” is upright to you. 5. Locate the “e” under low power. Q#6 What is the position of the “e” viewed with the microscope compared to its position on the stage? 6. As you are looking through the eyepiece, slowly move the slide from left to right. Q#7 In what direction does the letter move as seen through the microscope? 7. Now while you are looking through the eyepiece, move the slide toward you. Q#8 In what direction does the letter move as seen through the microscope?

Part C: A microscopic view of a macroscopic object 1. Add a drop of water to your slide. 2. Pluck a piece of hair from your head. Have your partner do the same. 3. Place them side-by-side on the slide. 4. Examine under low power, than high power Q#9 Describe your hairs….how are they similar….how are they different?

Part D: The importance of stains as an aid to microscope work 1. Add 1 drop of water to your slide. 2. Obtain potato scrapings 3. Swirl the scrapings in the drop of water. 4. Place the coverslip on the slide. 5. View the slide under low power. You may need to adjust the diaphragm. 6. Look for small colorless grains. You should be able to see cell walls surrounding groups of “grain packets” by slightly moving the fine adjustment knob to focus up & down. Q#10 Why does a specimen to be viewed under a microscope need to be thin? 7. Remove the slide. 8. Do not remove coverslip, add a drop of iodine to one edge of the coverslip. It will gradually move under the coverslip and stain the starch granules, or you can place a little piece of paper towel at the opposite end of the drop of iodine and it will diffuse through. 9. Observe the stained grains using low power. Q#11 Describe what you see before and after the addition of the iodine DO NOT CLEAN YOUR SLIDE YET, YOU NEED IT FOR NEXT PART Part E: A comparison of fields of view Field of view is the area seen through a microscope. This exercise will help you find out whether the field of view is greater with the low power or the high power. When using low power, the total area of your field of view is greater than when using high power. The width of your low power field is usually 4 times greater than that of your high power field. Low power has a width that is 4 times larger than that observed under high power. 1. Move the slide to a less crowed area of starch grains. Q#12 Record the number of grains observed under low power? 2. Without moving the slide, examine the same area of starch grains under high power. Q#13 Record the number of grains observed under high power? Q#14 Did you observe more or fewer starch grains under low power as compared to high power? Q#15 Did you observe more or less area under low power as compared to high power?

Clean and dry your slide and coverslip with paper towel

Part F: Depth of field 1. Add 1-2 drops of water to your slide. 2. Make an X in the middle of the water using one dark thread and one light thread. 3. Locate the center of the X under low power. Q#16 Can both the strands of thread be observed clearly at the same time under low power? 4. Change to high power and observe both strands at the point where they cross. Q#17 Can both strands be observed clearly at the same time under high power? Q#18 Using the information learned in Part E explain your answers to Q#16 & 17.

Part G: The Clean Up!! If not done properly, points will be deducted from your lab grade!!! Clean and dry your slide and coverslip. Place slide and coverslip in tray where you found them.

Take care of the microscope by doing the following: Unplug microscope Low power objective in position. Place stage in the uppermost position. Wrap cord around the base. Place plastic cover over microscope. Place in the center of your side of the table, with the class copy of the lab under it.

Use clean to wipe down table

Throw away any trash. Set all materials in place where you found them. Push in lab chairs. Turn in answer sheet to basket on my desk. Make sure your names are on it.