Sept. 19th Lab Report Handout:: Using the Compound Microscope

Using the Compound Microscope
Information

The microscope is designed for the study of objects too small to be seen with unaided eye. In work with organisms, biologist use differnt types of microscopes with various powers of magnification. Various models of the compound microscope magnify up to 1,000 times (abbreviated 1,000x). Electron microscopes magnify to more than 100,000 times (100,000x). Usually, you will work with a compound microscope that magnifies images form 100x to 430x. The microscope is the most important tool you will in biology.

Part A. Setting up the microscope

Locate on your microscope the parts in the diagram below:


Take a few moments to familiarize yourself with the parts of the microscope.


Part B: How to Prepare Materials

In a newspaper, find some fine print that includes a lower case “e”. Cut this letter from the news paper in a piece about 1 cm square. Pick up your slide an cover glass and place the piece of newspaper on the center of the slide, with the letter “e” right side up. With a medicine dropper put one drop of water on the piece of paper and put the cover glass over the paper. You have now prepared a wet mount of a piece of paper.

Part C: How to Focus the Microscope

Place the prepared slide on the stage of the microscope under the low power objective. Center the “e” on the slide over the opening in the stage.

While looking through the ocular slowly turn the course adjustment to lower the body tube until the printed letter comes into view. Then turn the fine adjustment of make the focus as sharp as possible.

1. How does the image of the letter “e” that you see through the microscope differ from its actual orientation on the slide?


2. Now slowly move the slide on the stage from right to left. Which way does the image that you see through the microscope move.



3. Move the slide away from you. Which way does the image move?



Determining Size Under the Microscope
Information
Not only does the microscope reveal objects invisible to the unaided eye, but it can also be used to measure tiny objects. Quantitative biological data are thus obtained. The more accurate your measurements, the more precise will be you date conclusions.
Measurements in science are made in the metric system. It is an easier system to use than any other because metric units are always related to one another by powers of 10.The basic unit of length in the metric system is the meter, slightly longer than a yard in the English system. Extremely small units of the metric system are used to measure things that can be seen only with the aid of a microscope.
Units of the Metric System
FRACTIONAL PARTS METRIC PREFIXES METRIC UNITS
1/10 or 0.1 deci- 1 decimeter (dm)
1/100 or 0.01 centi- 1 centimeter
1/1000 or 0.001 milli- 1 millimeter
1/millionth or 0.000001 micro- 1 micron (μ)
1 billionth or
.000000001 millimicro- 1 millimicron
1/10 billionth or
0.0000000001 1 Angstrom
Part A: Measurements Under the Microscope
The magnification of a microscope is the product of the magnification of the lenses in the ocular times the magnification of the lenses in the objective. These magnifications are usually stamped on the ocular and the objective.

1. If the ocular is stamped “10x” and the low-power objective is stamped “10x” what is the total magnification of the microscope under low power?



2. Check the ocular on the microscope you are using and the objectives. Calculate the total magnification of each of the oculars below:



An image of 90x or 250x or any other magnification is the indicated number of time longer and wider r than the object being viewed. But what is the original size of the object?

How can you measure a magnified image?

Method number 1:
Determining the diameter of the field of view using each objective:

1. Swing the objective down to low power.
2. Position the millimeter ruler so that the scale cuts across the center of the field. Focus on the part of the scale in view and read the diameter of the field in millimeters. Draw what you see below. Repeat for the second highest objective, but not the highest.

Magnification: Magnification:
Field of view in microns: Field of view in microns:

3. Convert your measurements into microns (millimeters multiplied by 1,000) and record above.
4. The ruler will not fit under the high powered objective, so how can we determine what diameter the field of view is in microns?






5. Use the ratio method to calculate the field of vision of the medium powered objective and compare to the value you got from measuring it.








6. Now let’s estimate the size of some single cells using what we know about the field of vision looking at medium and high power:

Amoeba: Draw a single amoeba in each space. Determine the size using the medium objective and draw details under the higher objective.

Magnification: 100x Magnification: 400x
Estimated size in microns: Comment on size and details


Frog Blood: Draw a single cell outline in the first space. Determine the size using the medium objective and draw details under the higher objective.

Magnification: 100x Magnification: 400 x
Estimated size in microns: Comment on size and details





Bacteria: Draw a single cell outline in the first space. Determine the size using the medium objective and draw details under the higher objective.


Magnification: Magnification:
Estimated size in microns: Comment on size and details





Questions:
1. Are single cells all the same size?


2. Are the cells we looked at prokaryotic or eukaryotic cells? In each case explain why you think so.




3. Without looking anything up, speculate on why an amoeba is the size that it is and the advantages and disadvantages of its size are.




4. Please don’t alter what you have already written, then look up the amoeba in your textbook or on line and compare what you have learned about it to what you inferred about it.




5. Without looking anything up, speculate on why a frog blood cell is the size that it is and what the advantages and disadvantages of its size are.





6. Please don’t alter what you have already written, then look up the function of blood cells in your textbook or on line and compare what you have learned about it to what you inferred about it.






7. Without looking anything up, speculate on why an bacterium is the size that it is and the advantages and disadvantages of its size are.



8. Please don’t alter what you have already written, then look up bacteria in your textbook or on line and compare what you have learned about it to what you inferred about it.