35
0 -m i n u t e s
es
si
RY
1–2
o5
ACTIVIT Y OVERVIEW
LA
O
40
-t
on
A License to Learn
BO RA
T
SUMMARY
Students learn how to use a microscope.
KEY CONCEPTS AND PROCESS SKILLS
1.
The microscope can be used as a tool for investigation.
2.
Proper use of the microscope protects the microscope from being damaged
and yields clearer information.
3.
Microscopes reveal organisms that cannot be seen with the naked eye.
KEY VOCABULARY
field of view (optional)
magnify/magnification
MATERIALS AND ADVANCED PREPARATION
For the teacher
*
1
Transparency 35.1, “Bubbles, Dust, or Micro-Life?”
1
transparency of Student Sheet 35.1, “Microscope Review” (optional)
1
overhead projector
For the class
*
1
*
microscope video camera (optional)
miscellaneous prepared slides, such as cat hair, bee stinger, the letter e, thread,
etc. (optional)
For each group of four students
1
plastic cup, half-full of water
1
dropper
water
*
*
1
scissors (optional)
Teacher’s Guide
C-71
Activity 35 • A License to Learn
For each pair of students
*
1
microscope slide
1
coverslip
1
microscope
*
lens paper
*
various materials, such as a comic strip, newspaper text, human hair, leaves, etc.
*
1
piece of paper towel
*
1
toothpick (optional)
For each student
1
Student Sheet 35.1, “Microscope Review” (optional)
1
Student Sheet 35.2, “What Does Magnification Mean?” (optional)
1
Microscope License
*Not supplied in kit
In this activity, you offer the students the opportunity to earn a microscope license after
they have demonstrated an understanding of proper microscope use. Check whether
students have used microscopes before. If so, you may wish to skip this activity.
Decide how you will assess students’ knowledge. In order to ensure a 100% passing
rate (so that all students can participate in the microscope labs), consider developing
a short performance assessment or a simple true/false, short answer, or other type of
quiz that students must pass in order to receive a microscope license. Be prepared to
offer the assessment before students move on to Part Two.
Gather material for students to observe in advance. Comic strips or color photos from
newspapers, in which the individual dots of color can be observed under magnification, are typically of high interest. Text from a newspaper helps students to observe
the inversion of the image caused by the microscope. Prepare a list on the board or a
transparency of the materials that will be available for students to observe.
If your school has a microscope video camera, use it for this activity. It will allow you
to project images viewed through the microscope onto a TV monitor. With the video
camera, you can show the whole class what to look for and what dust and bubbles look
like. Many microscope video cameras can also be used without the microscope attachment and can be used to show the class a student project, a dissection, or an image
from a book. Practice using the microscope video camera in advance of the activity.
C-72
Science and Life Issues
A License to Learn • Activity 35
TEACHING SUMMARY
Getting Started
1.
Demonstrate the parts of the microscope and their uses.
2.
Students earn a microscope license.
Doing the Activity
3.
Students use microscopes to observe everyday materials.
Follow–Up
4. Discuss how levels of magnification are calculated.
INTEGRATIONS
Math
Discussions of magnification can be integrated with discussions of powers of 10 and
place value.
BACKGROUND INFORMATION
Microscopes
The optical properties of microscopes responsible for magnifying and inverting an
image are due to the convex lenses in the objective and the eyepiece. The objective
magnifies and inverts the image. The ocular (eyepiece) further magnifies the image,
but does not invert it.
Teacher’s Guide
C-73
A License to Learn • Activity 35
TEACHING SUGGESTIONS
GETTING STARTED
1.
Demonstrate the parts of the microscope
and their uses.
Explain to students that, just as drivers need a dri-
demonstrated this competency, use the Microscope
License Template provided at the end of this activity (or create your own version) to provide each student with his or her own microscope license. Consider reproducing the licenses on colored paper and
laminating them after they are signed by the students.
ver’s license, students will require a microscope
DOING THE ACTIVIT Y
license in order to do the microscope lab activities.
(While it is not necessary to provide students with
a microscope license, the license can provide significant motivation to students of this age.)
3.
Students use microscopes to observe
everyday materials.
Have students read Part Two of the Procedure and
Familiarize students with the parts of the micro-
then demonstrate how to prepare a slide. Common
scope by displaying a microscope and identifying
mistakes students make when preparing wet
those parts that you wish students to know. You can
mounts include putting the drop of water on top of
provide students with Student Sheet 35.1, “Micro-
the coverslip, using too large a sample of material,
scope Review,” so that they can refer to each part of
or adding too much water to the slide. Emphasize
the microscope.
that dropping the coverslip at an angle minimizes
Briefly review how to use each part of the microscope. Be sure to include the idea of centering the
object under observation and focusing first at low
power. Students can then switch to medium power.
trapped air bubbles. If you have toothpicks available, students can gently tap the coverslip to eliminate any remaining bubbles. Excess water can be
soaked up with a small piece of paper towel.
This will be important preparation for using the
Demonstrate how to adjust the amount of light by
high power objective.
opening and closing the diaphragm. In general, a
Use “Rules for Handling a Microscope,” on page C24 in the Student Book to summarize classroom
expectations for microscope use. You may wish to
add other expectations to this list.
2.
Students earn a microscope license.
As described on page C-24 in the Student Book,
assess students on their knowledge of proper microscope techniques. Decide the minimum level of
more open diaphragm is preferable at higher
power. Show students how to focus first on low
power and then on medium power. Then demonstrate how to carefully rotate to the highest power
objective without hitting the slide, which might
crack the slide or damage the objective. Depending
on your microscopes, students may have to lower
the stage slightly before rotating the highest power
objective into place.
competency students must demonstrate before
Use Transparency 35.1, “Bubbles, Dust, or Micro-
receiving a microscope license. After students have
Life?” to model common mistakes when trying to
Teacher’s Guide
C-75
Activity 35 • A License to Learn
focus on a specimen. Students frequently mistake
would appear to be 40 mm long. Ask them to com-
an air bubble or other debris as the material that
pare the magnification for their smallest objective
they are trying to magnify.
to their estimate.
Point out the list of materials available for observa-
If you plan to use it, distribute Student Sheet 35.2,
tion that you have posted on the board or written
“What Does Magnification Mean?” Have students
on a transparency. Have students prepare and
complete it in class or for homework.
examine their slides. Circulate around the room,
helping students as needed and allowing students
SUGGESTED ANSWERS
who are able to focus to help others. If you wish,
TO ANALYSIS QUESTIONS
you can also have some prepared slides of cat hair,
bee stingers, etc. available for students to practice
1.
How does the microscope change the image
you see? Hint: Compare the material you
their microscope skills.
placed on the stage with what you see through the
eyepiece.
FOLLOW–UP
The microscope flips the image upside-down
4.
Discuss how levels of magnification are
and reverses it left to right. It also increases the
calculated.
amount of detail that you can see, which also
Encourage students to discuss their observations
means that you see less of the material (within
more precisely and to describe specific differences
the field of view). Students may point out that
in the images as the level of magnification
the material appears larger than it really is. Clar-
increased.
ify that this is because the material has been
magnified and not because the material has
Ask students to estimate how many times their
changed in size.
microscope enlarged or magnified the object when
they used the lowest power objective. When stu-
2.
Describe how the material(s) that you
dents have shared their estimates of magnification,
observed looked under low vs. medium
tell them how magnification is calculated—by mul-
power. What differences did you observe? How did
tiplying the magnification provided by the eyepiece
this compare to what you saw with your eyes?
(ocular) times the magnification provided by the
A likely response is that the material looked
objective. Ask students to find the magnification
larger or closer up with the higher power. Many
written on their eyepieces and on the lowest power
features of the material may not have been vis-
objective they were using. Give students a moment
ible with the naked eye; the microscope reveals
to calculate the magnification of their microscopes
additional, often surprising, levels of detail as
on the lowest objective. This will usually be a mag-
the magnification is increased.
nification of 4 (for the objective) times 10 (for the
eyepiece), giving a magnification of 40X. A magnification of 40X means that an object 1 mm long
C-76
Science and Life Issues
3.
The microscope is one important tool used
by scientists to study living things. What
A License to Learn • Activity 35
other tools are used by life scientists? Think about
3.
a. With a 2x eyepiece and a 3x objective,
tools used by doctors and in laboratory and field
the circle would be magnified six times
research. List three tools used by life scientists and
(2 x 3 = 6). Students often add, instead of
describe the kind of information they can help sci-
multiply, the magnifications.
entists collect.
b. Since the circle has a diameter of 0.5 cm,
Doctors use stethoscopes to monitor heart-
it would appear to have a diameter of 1
beats, thermometers to take temperatures, and
cm if magnified 2x (eyepiece alone) (0.5
x-rays to examine internal organs. In the labo-
x 2 = 1).
ratory, life scientists use spectroscopes to ana-
c. Since the circle has a diameter of 1 cm
lyze materials, scales to weigh materials, and
when seen with the 2x eyepiece alone, it
meters to determine the pH of a sample. In the
would appear to have a diameter of 3 cm
field, scientists use binoculars to see distant
when the eyepiece is combined with a 3x
objects, chemical kits to test water, and bands
objective (1 x 3 = 3, or 0.5 x 6 = 3).
to track the movement of animals.
d. Six times bigger (6x).
Suggested Answers to Student Sheet 35.2,
4.
“What Does Magnification Mean?”
a. The object is magnified 40 times (the
original line is 0.4 cm, while the magni-
1.
Answers will vary depending on classroom
fied image is 16 cm. 16/0.4 = 40). The
microscopes. However, answers for the most
width is also 40 times larger, but difficult
commonly found magnifications are shown
to measure.
below.
b. 4x objective (40/10 = 4).
Power
Eyepiece
Objective
Total
Magnification
Low
10x
4x
40x
10x
10x
100x
10x
40x
400x
Medium
High
2.
Eyepiece
Magnification
Objective
Magnification
Total
Magnification
10x
4x
40x
10x
20x
200x
5x
12x
60x
15x
40x
600x
Teacher’s Guide
C-77
A License to Learn • Activity 35
MICROSCOPE LICENSE TEMPLATE
MICROSCOPE LICENSE
MICROSCOPE LICENSE
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
DATES VALID:
DATES VALID:
Student Name
Authorized by
Student Name
Authorized by
MICROSCOPE LICENSE
MICROSCOPE LICENSE
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
DATES VALID:
DATES VALID:
Student Name
Authorized by
Student Name
Authorized by
MICROSCOPE LICENSE
MICROSCOPE LICENSE
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
DATES VALID:
DATES VALID:
Student Name
Authorized by
Student Name
Authorized by
MICROSCOPE LICENSE
MICROSCOPE LICENSE
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
Congratulations! You have demonstrated
the knowledge of microscope parts and
handling rules required to correctly operate a light microscope.
DATES VALID:
DATES VALID:
Student Name
Authorized by
Student Name
Authorized by
Teacher’s Guide
C-79
Name
Date
©2006 The Regents of the University of California
Microscope Review
Science and Life Issues Student Sheet 35.1
C-81
Name
Date
What Does Magnification Mean?
1.
Examine your school microscope. What are the possible magnifications?
Power
Eyepiece
Objective
Total Magnification
Low
Medium
High
2.
Calculate the total magnifications for the following microscope lenses:
Eyepiece Magnification
3.
Objective Magnification
10x
4x
10x
20x
5x
12x
15x
40x
Here is a small object.
a.
How much bigger do you think it would look under a microscope with a 2x
eyepiece and a 3x objective? Write your prediction below.
b. Draw the object as it would look
if magnified 2x. Use a ruler to
double its diameter.
©2001 The Regents of the University of California
Total Magnification
d.
c. Now draw what your drawing
in 3b would look like magnified
3x. Use a ruler to triple its diameter.
Use your ruler to compare the length of your second drawing (3c) to the
tiny object you were given at the beginning of this chapter. How many
times bigger is the image?
Science and Life Issues Student Sheet 35.2
C-83
Name
Date
Problem-Solving Model 1
4.
Here is another small object:
Here is a magnified image of that object:
What is the magnification?
b.
What was the strength of the objective lens used, if the eyepiece was 10x?
©2006 The Regents of the University of California
a.
Science and Life Issues Student Sheet 35.3
C-85
Bubbles, Dust, or Micro-Life?
Air Bubble
Dust
dust
coverslip edge
©2006 The Regents of the University of California
Micro-Life
microbe
debris
From a hay infusion at
Lawrence Hall of Science. Your
slide may look different.
Science and Life Issues Transparency 35.1
C-87