Download Using a Compound Microscope

Biology 1 Lab
Name: ____________________
Lab station #: ______________
Class period #: ______________
Using a Compound Light Microscope
In this investigation, you will use a compound light microscope to determine the positions and
sizes of objects. Before you begin, read the safety rules described in Appendix B (p. 1066). Then
read Appendix D to learn how to use a microscope (p.1070).
Purpose:
To learn the proper use of the compound light microscope and the types of
observations and data that can be collected.
Pre-lab Demonstration
Successful Demonstration ________________
INSTRUCTOR’S SIGNATURE
Before you can begin this lab, you must demonstrate to your instructor the proper use of the
microscope. This will require you to do the following successfully:
1)
2)
3)
4)
5)
Proper use and care of the microscope.
Making a wet mount slide.
Changing slides.
Demonstrate the ability to focus the microscope using all three objectives.
Proper storage of the microscope.
Failure to demonstrate proper use of the microscope will result in a “0” on this lab.
Materials
• compound microscope
• microscope slide
• newspaper or other small-print text
• scissors
• dropper pipette
• cover slips
• slide of crossed threads fibers
• transparent 15-cm plastic ruler
• prepared slides of bacteria and plants
Skills Observing, Measuring, Calculating
Define the following:
Magnification: _____________________________________________________
________________________________________________________________
Resolution: ______________________________________________________
________________________________________________________________
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Calculating Total Magnification
Magnification of a compound light microscope is based on the combined magnification of all
lenses used to observe the specimen. Your microscope uses two sets of lenses, the ocular
(eyepiece) and the objective lens. The total magnification is calculated be multiplying the
magnification of the ocular by the magnification of the objective. The ocular has a magnification
of 10X. Complete the table below:
Data Table 1: Total Magnification
Name of Objective
Objective
Magnification
Scanning
4X
Low
10X
High
40X
Work
Total Magnification
10X x 4X
40X
Procedure
1. Use scissors to cut out a square of printed text approximately 1 cm per side. Place the paper
square on a microscope slide. CAUTION: Be careful when handling sharp instruments.
2. Making a wet-mount slide (p. 1071) Use a dropper pipette to place a drop of water on the
paper square. Add a cover slip. Place the slide on the stage of a compound microscope. Use the
stage clips to hold the slide. Position the slide in a way that allows the specimen to be
illuminated by the light passing through the stage.
3. Use the scanning objective to bring the letters on the paper square into focus. How does the
orientation of the letters observed through the microscope compare with the letters when
observed without looking through the microscope?
____________________________________________________________________________________
Diagram what you see using the scanning objective. Slowly move the slide in different
directions along the stage. CAUTION: Handle the microscope carefully.
a. What is the total magnification used in your diagram?______________
b. When you move the slide to the left, what direction does it appear to
move?
_________________________________________________________________
c. What happens when you move it away from you?
_________________________________________________________________
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4. Pick one letter and move your objective to the low-power objective and focus in on that letter.
Diagram your observations below. What appeared to happen to your field of view?
________________________________________________________________
________________________________________________________________
What happens when you move diaphragm lever? _____________________
_________________________________________________________________
________________
Total Magnification
5. Observe the crossed threads slide. Focus on the location where the threads cross. Use the
magnification that allows you to determine what order the threads are stacked. Diagram your
observations below. What is the order of the threads (top-middle-bottom)?
Top thread color: ______________________
Middle thread color: ___________________
Bottom thread color: ___________________
What slide box are you using? ___________
________________
Total Magnification
6. Prepare a wet mount slide of crossed fibers using strands of different color hairs from
members of your group. Diagram your observation on scanning and then move to low power
objective. Using the fine adjustment to focus up and down through the area where the fibers
cross.
Which strand of hair is on top?
_____________________________________
Label the colors of the strands and position (top and
bottom) on your diagram.
____________
T. Magnification
______________
T. Magnification
The Science of Biology Exploration
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7. Observe a transparent ruler through the scanning-power objective. Use the ruler to measure in
millimeters, the diameter of your field of view as precisely as you can through the center.
Record this distance and the total magnification of the scanning objective in data table 2 and in
step 1 of #8 below.
8. To calculate the diameter of the other objectives, use the following formulas:
1) Convert the diameter of the scanning field of view to micrometers (1mm = 1000m):
Diameter of scanning field of view is: ______ mm X 1000 = ________ m (use in #3)
2)
Magnification of low powered objective = A (use in #3)
Magnification of scanning objective
3)
Diameter of Scanning field of view (from # 1) = diameter of low powered objective
A (from # 2)
4)
Repeat 2 and 3 for the high powered objective. In step 2, replace the magnification of the low
power objective with the magnification of the high powered objective.
For example: if the magnification of the scanning objective is 12 and the magnification of the high
powered objective is 48, than A = 48/12 = 4. If the diameter of the scanning objective is 1600m, the
diameter if the high powered field of view = 1600 / 4 = 400m.
Data Table 2: Field of view measurements
NAME OF OBJECTIVE
MAGNIFICATION
DIAMETER OF FIELD OF VIEW
a. Do your measurements agree with what was observed about the field of view in step 4?
Explain. ______________________________________________________________________
______________________________________________________________________________
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b. Why is this information important when moving from one magnification to another? How
should this information be used?
9. Examine a prepared slide of the Allium root slide at scanning, low, and high powers. The
small round shapes you see are cells. Diagram your observations below. Use the field diameters
you calculated in step 8 to estimate and record the size of a typical plant cell. For example, if 4
cells fit across an 800-micrometer field of view, then each cell is 200 micrometers long.
Observation:
Magnification:
__________________
Diameter:
__________________
Number of cells across: __________________
Length of single cell:
__________________
Magnification:
__________________
Diameter:
__________________
Number of cells across: __________________
Length of single cell:
__________________
Use the pointer to help count the cells. The pointer is about half the diameter of the field of view.
Magnification:
__________________
Diameter:
__________________
Number of cells across: __________________
Length of single cell:
__________________
Average Allium root cell size: _________________
𝑫𝒊𝒂𝒎𝒆𝒕𝒆𝒓 𝒐𝒇 𝒇𝒊𝒆𝒍𝒅 𝒐𝒇 𝒗𝒊𝒆𝒘
= 𝒍𝒆𝒏𝒈𝒕𝒉 𝒐𝒇 𝒔𝒊𝒏𝒈𝒍𝒆 𝒄𝒆𝒍𝒍
# 𝒐𝒇 𝒄𝒆𝒍𝒍𝒔 𝒂𝒄𝒓𝒐𝒔𝒔
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10. Repeat step 9 with a prepared slide of bacteria (typical Bacillus) using only high power.
Magnification:
__________________
Diameter:
__________________
Number of cells across: __________________
Length of single cell:
__________________
11. How do the size of bacteria cells compare to the size of a plant cell? Estimate how many
times larger one cell type is to the other cell type.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
12. What are the advantages of using the high-power objective? What are the disadvantages?
________________________________________________________________________
13. Inferring Some plant diseases are caused by bacteria.
a. Could a bacterium injure a plant by surrounding a plant cell and consuming it?
________________________________________________________________________
b. By entering plant cells?
________________________________________________________________________
c. Support your answer using specific data from the lab.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
14. Critical Thinking: How does resolution limit magnification?
________________________________________________________________________
________________________________________________________________________
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