LAB Learning to Use the Microscope

NAME: ______________

LAB: Learning to Use the Microscope

Introduction

    "Micro" refers to tiny, "scope" refers to view or look at. Microscopes are tools used to enlarge images of small objects so as they can be studied. Microscopes range from a simple magnifying glass to the expensive electron microscope. The compound light microscope is the most common instrument used in education today. It is an instrument containing two lenses, which magnifies, and a variety of knobs to resolve (focus) the picture. It is a rather simple piece of equipment to understand and use. In this lab, we are going to learn the proper use and handling of the microscope.

Materials:

 Compound microscope (at station) Glass slides 

 Cover slips  Pipet

 Beaker of water  Scissors

 The letter "e" cut from newsprint      Threads (on the front table) 

 Ruler Cotton

 Stain

Procedures

Proper Handling of the Microscope

1. Remove the dust cover and store it properly (folded neatly and set aside). Plug in the scope. Do not turn it on until told to do so.

2. Examine the microscope and give the function of each of the parts found on the following page. Label the diagram (you can use the name or the letter).

a. Eyepiece

b. Body tube

c. Objectives

d. Stage

f. Diaphragm

g. Coarse adjustment

h. Fine adjustment

i. Base

-Examination of the microscope parts –

at this point you should turn the microscope on…

1.

 Locate the diaphragm under the stage. Move it to different settings and note the changes in light intensity as you do so.

 Which setting makes the specimen the lightest? The darkest? _______________________________________

_______________________________________

2.

 Twist the ocular lens; does yours have a pointer? ____________

 What is the purpose of the pointer?

__________________________________________________________________

 What happens to your viewing field if you do not have an objective fully clicked into place? (try it to see)

__________________________________________________________________

Determining Total Magnification:

 Eyepiece magnification

______________ (X) Objective magnification______________ = Total Magnification_____________X

  Eyepiece magnification

______________ (X) Objective magnification______________ = Total Magnification_____________X

3. Write out the “rule” for determining total magnification of a compound microscope.  

Making a Wet- Mount Slide

1. Gather a few strands of cotton from a cotton ball using forceps. If your specimen is too thick, then the cover slip will wobble on top of the sample like a see-saw, and you will not be able to view it clearly. It should look like a thin spider-web.

2. Place ONE drop of water directly over the specimen. If you put too much water, then the cover slip will float on top of the water, making it hard to draw the

specimen, because they might actually float away. (Plus too much water is messy) 3. Place the cover slip at a 45 degree angle (approximately) with one edge touching the water drop and then gently let go. Performed correctly the cover slip will perfectly fall over the specimen.

Draw the specimen as it appears in your viewing field under low, medium, and high power. Rules for drawing specimens:

1. Use pencil - you can erase and shade areas

2. All drawings should include clear and proper labels (and be large enough to view details). Drawings should be labeled with the specimen name and magnification.

3. Labels should be written on the outside of the circle. The circle indicates the viewing field as seen through the eyepiece, specimens should be drawn to scale - i.e...if your specimen takes up the whole viewing field, make sure your drawing reflects that.

Staining a Specimen (use the same slide/specimen as above)

1. Without lifting the coverslip off the cotton, place one drop of stain (methylene blue) on the edge of the cover slip. (see picture below)

***Caution: Methylene Blue will stain clothes and skin!

2. Place the flat edge of a piece of paper towel on the opposite side of the cover slip. The paper towel will draw the water out from under the cover slip, and the cohesion of water will draw the stain under the slide. (see diagram below)

3. As soon as the stain has covered the area containing the specimen, you are finished. The stain does not need to be under the entire cover slip. If the stain does not cover as needed, get a new piece of paper towel and add more stain until it does. 4. Be sure to wipe off the excess stain with a paper towel.

Draw your specimen as it appears under each different power. It may appear darker  or lighter in spots. Use shading to show darker and lighter spots.

Low Power (4x) Medium Power (10x) High Power (40x)

Depth Perception

Have one partner prepare a new slide of threads by placing 3 different color threads across one another. Add a drop of water and a cover slip. You will only need to view it under low power at this point. The other partner’s task is to figure out which thread is on top, which is in the middle, and which is on bottom using the

come into focus at different times. The one that comes into focus the first should be the top thread.

 What is the color order of your threads? (your partner will tell you if you are correct)

Preparing a wet mount of the letter "e”.

With your scissors cut out the letter "e" from the newsprint – be sure to use a lowercase “e” that is from the main body of an article. Place it on a clean glass slide so as to look like (e). See the figure below.

Make a wet mount slide of the letter “e” (as done with the cotton earlier). Turn on the microscope and place the slide on the stage; making sure the "e" is facing the normal reading position (see the figure above). Using the course focus and lowest power, move the body tube down until the "e" comes into view. It may be blurry but you can see it. Now, use the fine adjustment knob to focus until it can be seen clearly. Draw what you see in the space below in the Low Power (4x) circle. Change the scope to Medium Power (10x). On medium power DO NOT touch the coarse adjustment knob, instead use only the fine focus to clarify the picture. Draw what you see in the space below in the Medium Power (10x) circle. Finally, change the objective lens to the High Power (40x). Again, DO NOT touch the coarse

adjustment knob - instead use only the fine focus to clarify the picture. Draw what you see in the space below in the High Power (40x) circle.  

Go back to the lowest power. Center and focus on the “e”.

1. Describe the relationship between what you saw through the eyepiece and what you see on the stage.

3. Looking through the eyepiece, move the slide to the upper right area of the stage. What direction does the image move?

4. Now, move it to the lower left side of the stage. What direction does the image move? 

5. Explain the differences between what you saw (your observations) under each power of the microscope looking at the same slide

Measuring with a Microscope

Use a clear ruler (or just the edge of a white ruler) to determine the width of the viewing field under the scanning objective. Position the ruler so that the millimeter marks are visible in your viewing field. Remember that there are 1000 micrometers in a millimeter.

 Estimate the length (diameter) of your viewing field in micrometers

You cannot use this method to determine the diameter under high power (try switching objectives). Instead you can use a mathematical proportion method to determine the diameter under high power.

High power field diameter = low power field diameter x low power magnification / high power magnification

Directions for Cleaning up:

o

Remove the slide from the stage and clean it

o

Separate the cover slip and the slide

o

rinse them both under water

o

dry them off

o

return to box

o

Turn off the microscope

o

Wind up the cord so it resembles its original position

o

Place the low power objective in place

o

Lower the stage all the way down

o

Cover the scope with the dust cover

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Part 2

Investigation of a Large Specimen

Light microscopes are only useful for viewing small thin specimens. In Biology, you will perform dissections on larger specimens and may need to magnify the area of interest. In this situation, a stereoscope may be the best instrument. Stereoscopes present a larger field of viewing and handle depth much better than the light microscope. The drawback of the stereoscope is that it does not have a high magnification. Use one of the stereoscopes provided. Practice changing the light source and the focus on the stereoscope. Pick a specimen – did you bring in your own??? Determine which light and magnification is best for viewing that particular specimen and reasons why you think that is so.

Name of specimen ____________________________________________ Magnification _______________ Light ____________________

Reasons_____________________________________________________________ What details did you notice about the specimen that you did not see without using the stereoscope?