Microscope Lab - Using the Microscope and Slide Preparation

Examine the microscope and familiarize yourself with the parts of the microscope.

1. Magnification

The magnification written on the ocular lens (eyepiece) is _____________

The magnification on the Scanning objective ___________ Low Power Objective ___________
High Power Objective ___________

What is the total magnification for each lens (multiply ocular times objective)

Scanning _____________ Low Power ______________ High Power ________________

2. Diaphragm

Examine the diaphragm, what are the numbers written on it? ____________________

Which setting makes the specimen the lightest? ________________ The darkest? _______________

3. Lenses

Twist the ocular lens, does yours have a pointer? _____________ What is the purpose of the pointer? __________________________________________

Find out what happens to your viewing field if you do not have an objective fully clicked into place. ____________________________________________

4. Viewing a Slide

Obtain a prepared E slide. Focus the slide first with the scanning objective, then click to lower power and focus again. Finally, focus the slide under high power. Remember, at high power, you should ONLY use the fine adjustment knob.

Draw the E exactly as it appears in your viewing field for each magnification. The circles below represent your viewing field. The E should take up as much space in the drawing as it does in your viewing field while you're looking at it.

Scanning

Low Power

High Power

5. Depth Perception

Obtain a prepared thread slide. You will only need to view it under scanning at this point. Your task is to figure out which thread is on top, which is in the middle, and which is on bottom. You should notice that as you focus the thread, different thread will 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?

 

6. Making a Wet Mount of a 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 under High Power.

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 scanning, low and high power.

Scanning

Low Power

High Power

 

7. Staining a Specimen

1. Place one drop of stain (methylene blue) on the edge of the cover slip. 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.

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 low power. Used color pencils to show how the stain appears. It may appear darker or lighter in spots. Use shading to show darker and lighter spots.

Scanning

Low Power

High Power


8. Investigation of Pond Water

1. Prepare a wet mount of pond water - a sample of pond water is provided in a jar. The best specimens usually come from the bottom and probably will contain chunks of algae or other debris that you can see with your naked eye. (Be careful that your slide isn't too thick)

2. Use the microscope to focus on the slide - try different objectives, some may be better than others for viewing the slide..

3. Make three separate drawings below at different areas of the slide and at different magnifications. Label where appropriate.

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.

Scanning

Low Power

High Power

9. Investigation of Large Specimen

Light microscopes are only useful for viewing small thin specimens. In biology, you will perform dissections on larger specimens an 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. Examine one of the stereoscopes in the room. They will be positioned around the room with specimens.

Practice changing the light source and the focus on the stereoscope. For each specimen determine which light and magnification is best for viewing.

Name of specimen ____________________________________________

Magnification _________ Light ____________ Reasons _____________________________________________________________

 

10. Measuring with a Microscope

Use a clear 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

What is the diameter (in micrometers) of your high power field _____________________

Fill out the table below after viewing prepared specimens.

Name of Object Measurement of Object

 
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