CHAPTER INVESTIGATION
Using a Microscope
OVERVIEW AND PURPOSE The smallest forms of life
are not visible to the human eye. You will use a light microscope
as a tool to observe very small unicellular and multicellular organisms. Then you will compare the organisms you see under the
microscope to the Identification Key. Refer to pages R14 and R15
of the Lab Handbook for more information about using a microscope and preparing a slide.
Procedure
Make a data table like the one shown on page 199. To observe
the microscopic organisms, you need to make a wet-mount slide.
Obtain a slide and use the eyedropper to place 2–3 drops of
pond water in the center of the slide.
Obtain a cover slip for your slide. Place
one edge of the cover slip on the slide,
at the left edge of the pond water.
Slowly lower the cover slip as if you
were closing the cover of a book.
The cover slip should lie flat on the
slide. If you see air bubbles, pick up
the cover slip and lower it again.
MATERIALS
• slides
• eyedropper
• pond water
• cover slip
• light microscope
• lens paper
• Identification Key
lens
coarse
adjustment
nose
fine
adjustment
objective
slide
stage
198 Unit 2: Cells
step 2
Clean the lenses of the microscope with
lens paper. Choose the lowest magnification,
then place the slide on the stage. Start with the objective at its
lowest point and raise the objective to focus. First focus with the
coarse adjustment, which is usually the larger knob. Begin your
search for living organisms. Use the fine adjustment to make the
image clearer. Be patient when looking for life on your slide. It
may take some time.
When you find something interesting,
carefully switch to a higher magnification.
Turn the nose of the microscope until
another objective snaps into place. Use
only the fine adjustment when viewing at high power, to avoid scratching
the microscope or the slide. Move the
slide gently from side to side as you
look through the microscope. Search
different parts of the sample for different
organisms.
step 4
Identification Key
Euglena
Paramecium
Stentor
Desmid
Water flea
(unicellular)
(unicellular)
(unicellular)
(unicellular)
(multicellular)
Make a sketch of each of the different organisms
that you see. Record any movement or behavior
you observe. Include the magnification of the
objective lens that you used.
Observe and Analyze
Write
It Up
1. CLASSIFY Use the Identification Key
above to identify the organism. If you cannot
make an identification, write unknown.
Conclude
Write
Hydra
Copepod
Volvox
(multicellular) (multicellular) (multicellular)
INVESTIGATE Further
Collect a small sample of soil from outside
the school or your home. Mix the soil with
enough tap water to make it liquid. Then take
a sample of the soil mixture and examine
it under the microscope. Sketch some of the
organisms you see. Are they similar to those
in the pond-water sample? Why do you think
different types of organisms live in different
environments?
It Up
1. COLLECT DATA Compare your sketches
with those of your classmates. How many different organisms in total did your class find?
How many were identified as unicellular?
How many were identified as multicellular?
2. COMMUNICATE Why is the microscope
an important tool for studying cells and entire
organisms?
ope
Using a Microsc
Microorganisms
Table 1. Identifying
Organism 1
:
Magnification used
vior:
Movement/beha
Sketch:
3. INTERPRET Using what you learned in
this chapter and in this investigation, explain
the ways in which you would use the different objectives on a microscope.
Name:
4. APPLY Many diseases, such as strep throat,
are caused by microscopic organisms. Why
might a microscope be an important tool for
a doctor?
5. APPLY How might the way a biologist uses
Organism 2
:
Magnification used
:
or
vi
Movement/beha
Sketch:
a microscope be different from the way a
doctor uses a microscope?
Name:
Chapter 6: The Cell 199