Introduction to the Microscope Lab
Introduction: In biology, it is very important to be able to use a microscope with relative ease.
This set of experiments is designed to help you learn about the light microscope and how to use it to find and focus properly on a given specimen. If you are struggling as you go through these experiments, be sure to ask Mrs. Boron for help.
Experiment 1 – Focusing on a Specimen
1. Take a page of newspaper and cut out a single letter (the letter e or the letter r). The letter should be a normal size, not a letter from a headline or something large such as this.
2. Make a wet mount slide by using the following procedure (from now on if the lab requires a wet mount, this is the general procedure to use):
a. Obtain a clean microscope slide, a dropper with a cup of water, and a small square coverslip.
b. Place a small drop of water onto the center of the slide.
c. Place the letter you cut out of the newspaper onto the drop of water.
d. Place the coverslip onto the slide by angling it and putting the edge of the coverslip down first, and then slowly and carefully lowering the rest of the coverslip onto the slide. The goal is to minimize air bubbles. If you find you have a lot of air bubbles under the coverslip, remove the coverslip and try again.
e. Place the slide onto the stage of the microscope so that the letter is facing toward you, as if you were going to read it, and the letter is being illuminated from below.
3. Make sure the 4x objective lens is clicked into place and then look through the microscope.
4. While looking through the ocular lens, move the course focus knob so that the stage is moving closer to the objective lens until you can see the letter. Adjust the knob until the image is clear and crisp.
5. When you can see the letter crisply, answer the following questions and then call Mrs.
Boron over to check you off.
Questions:
1.1 How many times is the image magnified? (Take the ocular lens magnification multiplied by the objective lens magnification).
1.2 When you look at the letter, which way does the letter appear to be facing?
1.3 If you move the letter to the left, which way does it appear to move?
1.4 Based on the question above, whichever way you move the letter, the image appears to move __________________.
Mrs. Boron’s Initials_________
Experiment 2 – Focusing under High Magnification 6. Switch to the 10x objective lens.
7. Use the fine focus knob to adjust the image until it is crisp and clear. If the image is dim, adjust the diaphragm until the illumination is better.
Questions:
2.1 How many times is the letter magnified when using the 10x lens?
2.2 With the letter under a higher magnification, do you see more of the letter, or less?
2.3 Why shouldn’t you EVER use the course focus knob once you switch from the 4x objective lens?
2.4 Magnification is how much bigger the image has been made (how much it has been magnified) and resolution is how clear and crisp you can make the image. Please explain how these two concepts are related (Are you able to get equal resolution under all magnifications? Explain.)
Mrs. Boron’s Initials_________
Experiment 3 - Depth
8. Ask Mrs. Boron to give you a prepared slide of three different colored pieces of thread.
Don’t look closely at the slide!!! (No cheating!)
9. Put the slide on the stage of the microscope (make sure the 4x objective lens is in place!) and focus on the threads.
10. Use the objective lenses and focus knob to determine which color thread is on the bottom, which color is in the middle, and which color is on the top of the three threads. Write this order in the questions section below.
11. If you’re not already on it, switch to medium power.
12. Adjust the fine focus knob so that the top thread is in focus. There are little strands of thread coming off of each larger strand (like they’re fraying). Make sure these are in focus on the top thread.
13. Move the fine focus knob until the middle thread’s frays are in focus.
14. Move the fine focus knob until the lowest thread’s frays are in focus.
Questions:
3.1 What is the order of colored threads, from bottom to top?
3.2 Why didn’t the stragglers of all three threads appear crisp and focused at the same time?
3.3 Based on questions 3.2 and 3.3, what does the fine focus knob do?
Mrs. Boron’s Initials_________
Experiment 4 – Estimating Size and Drawing Skills
15. This experiment will not be done using an actual microscope. We will get back to the real microscopes in experiment 5. Obtain a petri dish, small metric ruler, a single piece of computer paper, a penny, a bean, and a binder clip and bring it back to your station.
16. Measure the diameter of the petri dish with the metric ruler. Be as accurate as possible!
Record your measurement in millimeters in 4.1 of the questions section.
17. Now drop the penny onto the piece of computer paper. Once it has been dropped, you cannot move it!
18. Place the petri dish over the coin. The circle of the petri dish represents the field of vision or circle of light that you see when looking inside the microscope.
19. Hold the petri dish steady in one place, and slide the paper around underneath it. Notice that you can move the coin around inside the petri dish by moving the paper.
20. Draw what you see in 4.1 of the questions section: a drawing of the petri dish and coin inside it. Do not trace the petri dish and the coin. Try to make the drawing to scale (have the same difference in size, even though the drawing is smaller than the actual petri dish).
21. The challenge now is to calculate how big your coin is without actually measuring it.
First, estimate out how many coins will fit across the diameter of the petri dish. (You can make “ghost coins” by sliding the paper under the petri dish to help you).
22. Divide the diameter, D, by the number of coins, X, to fit across the petri dish. Your answer is the size (diameter) of one coin, d.
d = D/X
23. See how accurate you were by using the ruler to measure the actual size of the coin.
Record this in 4.1 of the questions section.
24. Put the penny aside and place the bean on the computer paper. Repeat steps 20 through 23 for the bean, recording the information in 4.2 and 4.3 of the questions section. (You will have to do these steps twice for the bean – once for the length and once for the width).
Questions:
4.1 Record the following information from your experiment above:
Diameter of the petri dish = ________ mm
Estimate of number of pennies to fit across petri dish = ________
Calculation of size of penny:
________ / _________ = __________
Actual size of penny = ________ mm
Edge of ruler Field of view
Ruler Millimeter lines
4.2 For the length of bean:
Estimate of number of beans to fit across petri dish = ________
Calculation of length of bean:
_______ / _______ = _______
Actual length of bean = _______ mm 4.3 For the width of bean:
Estimate of number of beans to fit across petri dish = _______
Calculation of width of bean:
_______ / _______ = _______
Actual width of bean = _______mm
4.4 What did the piece of paper represent on the microscope? What did the penny/bean represent? What did moving the piece of paper represent?
Paper:
Penny/bean:
Moving paper:
Mrs. Boron’s Initials _________
Experiment 5 – Microscope Measurement
25. Put the clear ruler on the microscope stage so that you can see the millimeter scale under low power.
26. Place one millimeter marking of your ruler at the far left hand side of the low power field.
You should see one other millimeter marking in your field of mew. This means that your low power field is between 1 and 2 mm in diameter.
27. To determine the diameter of the low power field of your microscope, approximate, to the nearest 0.1 mm, what fraction of the second millimeter is in your field of view. Record this in 5.1 of the questions section.
28. Determine how many times larger your low power field is than your high power field by dividing your high power magnification by the low power magnification. Record this in 5.2 of the questions section.
29. Now determine the diameter of your high power field by dividing the diameter of your microscope’s low power field by the number you obtained in 28 above. Record this in 5.3 of the questions section.
Questions:
5.1 Diameter of low power objective = _________ mm 5.2 High Power Magnification / Low Power Magnification:
5.3 Low Power Diameter / answer from 5.2 Diameter of high power field:
5.4 Many of the specimens you will observe under the microscope will be smaller than 1 mm in size. Because of this, microscopic measurements are often expressed in microns (µm or micrometer). One millimeter equals 1,000 microns.
What are the diameters of your low and high power fields in microns?
Low Power Field = ________ µm High Power Field = ________ µm
Mrs. Boron’s Initials _________
