20
LESSON
KEITH WELLER, AGRICULTURAL RESEARCH SERVICE/UNITED STATES DEPARTMENT OF AGRICULTURE
The Key to Organisms—
An Assessment
There are many different species of fruits and vegetables
shown here. How could you develop a key with which to
INTRODUCTION
In this lesson, you will use what you have
learned about the organisms on the organism
photo cards to create two kinds of dichotomous keys for identifying those organisms.
Your teacher will introduce you to dichotomous keys during “Getting Started.” You will
practice constructing written dichotomous
keys that identify some of your classmates and
various organisms. Then you will create, on a
piece of poster paper, a graphical dichotomous
key for 13 of the organisms on the photo
cards. From this graphical key, you will prepare a written key and attach it to the poster.
OBJECTIVES FOR THIS LESSON
Develop written dichotomous keys for
various organisms pictured on Student
Sheets.
identify each species if the others were not present?
Create a graphical dichotomous key for
13 of the organisms on the organism
photo cards.
Develop a written dichotomous key from
the graphical dichotomous key.
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Getting Started
Listen and participate as your teacher guides
you through an activity that introduces you to
the concept of a dichotomous key.
MATERIALS FOR
LESSON 20
For each student
2 copies of Student
Sheet 20.1A:
Dichotomous Key
Template
For your group
2 copies of Student
Sheet 20.1B:
Organism Sets
1 copy of Student
Sheet 20.2:
Dichotomous Key
Template for
Organisms
1 set of organism
photo cards
1 sheet of poster
board or
construction paper
1 black marker
1 metric ruler, 30 cm
(12 in.)
Transparent tape
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LESSON 20
THE KEY
TO
ORGANISMS—AN ASSESSMENT
Inquiry 20.1
Creating Dichotomous Keys
Inquiry 20.2
Creating a Dichotomous
Key for 13 Organisms
PROCEDURE
PROCEDURE
Listen and participate as your teacher
1. demonstrates
how to prepare a dichotomous key to identify eight of the students
in your class. If you are one of the students chosen to be identified, ask a group
member to fill out the front of one of your
copies of Student Sheet 20.1A for you.
the cards for lima beans, yeast,
1. Remove
and duckweed from the full set of organism cards. You will use the remaining 13
cards for this inquiry.
will work with your group to develop
2. aYougraphical
dichotomous key on your
group’s poster paper for the 13 organisms.
First read the following example with
your group and ask questions to clarify
anything you don’t understand.
your teacher has guided you
2. After
through the classmate identification
activity, turn to the back of Student
Sheet 20.1A, on which you will find
another dichotomous key form. Place
the front of Student Sheet 20.1B where
you and your partner can see it. With
your teacher’s assistance, create a key to
identify the eight organisms pictured.
A.
Have a member of your group print the
title “Organisms” in the top center of the
poster paper. Place the 13 organism cards
with the photos face up, just below the
title on your poster paper. Pretend that
seven of the 13 organisms contain chlorophyll and six do not. If you were creating
a graphical dichotomous key for these
organisms, you would then divide the
organism cards into two groups—
“Chlorophyll present” on the left and
“Chlorophyll absent” on the right, as seen
in Figure 20.1. The shaded boxes represent the organism photo cards.
B.
There would now be seven organisms
under the title “Chlorophyll present.”
Working from left to right, identify the
organisms in the chlorophyll group before
working with the organisms in the
“Chlorophyll absent” group. Each time
you use another feature to divide the
organisms further, you would move the
photos down and under the feature they
match. For example, if you chose
“Flowers” and “No flowers” as your next
feature, you would use your ruler and a
Work with your partner to prepare a key
3. for
the eight organisms pictured on the
back of Student Sheet 20.1B. Write your
key on the front of the second copy of
Student Sheet 20.1A.
Your teacher will review the features you
4. used
to identify the second set of organisms. Make sure you clarify any points
you don’t understand.
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LESSON 20
C.
pencil to draw very light lines downward
from the term “Chlorophyll present.” You
would then print “Flowers” at the end of
the left line, and “No flowers” at the end of
the right line. You would move the three
photos of organisms with flowers below the
term “Flowers” and those of the organisms
that do not have flowers under the term
“No flowers,” as shown in Figure 20.2.
THE KEY
TO
ORGANISMS—AN ASSESSMENT
You would continue to work from left to
right until you had each photo under a
feature that applied only to that organism.
Under each organism photo card, you
would then print the name of the organism lightly in pencil. An example of a
completed graphical key is shown in
Figure 20.3.
Organisms
Chlorophyll present
Figure 20.1
Chlorophyll absent
Spacing is important so that all of the organisms, features, and lines fit neatly
on the poster.
Organisms
Chlorophyll present
Flowers
Figure 20.2
Chlorophyll absent
No flowers
Working from left to right, now deal with the three photos under the term “Flowers.”
Organisms
Chlorophyll absent
Chlorophyll present
Flowers
No flowers
Not yellow
Yellow
2 mm or more
in length
Under 1 mm
Under 2 mm
Eye spot
1 mm or more in length
No eye spot
No wings
Wings
Name
Name
Perfect Not perfect
Name
Name
Flagella
Name
1 flagellum
No flagella
More than
1 flagellum
Name
Name
Cilia
No cilia
Red
Not red
Name
Name
Name
Name
Name
Name
Figure 20.3
This is how the final key might appear. Your actual final key will depend on the features you choose.
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LESSON 20
THE KEY
TO
ORGANISMS—AN ASSESSMENT
this technique to create your own
3. Use
graphical dichotomous key. Check with
your teacher for approval before you use
a permanent marker to print the features
and names of organisms and to retrace
the penciled lines in marker.
Follow your teacher’s directions for
4. putting
the key into written form on
Student Sheet 20.2: Dichotomous Key
Template for Organisms, and for turning
in your work.
REFLECTING ON WHAT YOU’VE DONE
Participate in a class discussion about the
1. dichotomous
key you created. Be prepared to justify the descriptive terms you
used to divide your organisms.
back in your science notebook to
2. Look
your entries for Lesson 1. Look at the list
of questions about organisms for which
you wanted to find answers during this
module. On a fresh page, divide your
questions into two groups: those that
were answered and those that were not.
Discuss both lists with the class.
with the class how you could
3. Discuss
reinforce or build on what you have
learned in this module.
with the class things that you
4. Discuss
learned in this module that clarified some
misconceptions you may have had about
organisms.
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LESSON 20
THE KEY
TO
ORGANISMS—AN ASSESSMENT
One of the
Buggiest
Places on Earth
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Where can you find hundreds of species of
Visitors get to handle some of the world’s
organisms, each in its own habitat with other
most interesting insects. They also can closely
members of its species? Where can you see
observe spiders, crabs, and other arthropods.
hundreds of leaf-cutter ants parading around
“An arthropod,” Nathan explains, “is an invertewith bits of leaves that look like tiny green
brate with an exoskeleton, a segmented body,
flags? Or crawl through a make-believe termite
and jointed legs. Actually, the Insect Zoo could
mound? Answer: At the Insect Zoo in Washingbe called the Arthropod Zoo because many of
ton, D.C., in the Smithsonian Institution’s
the arthropods that live here aren’t insects.
National Museum of Natural History.
[The insects are the ones with six legs.] But
Entomologists and educators Nathan Erwin
Arthropod Zoo isn’t quite so catchy a name.”
and Faith Deering are the “keepers” of the
What is catchy is the thrill people feel when
Insect Zoo. Caring for the insects is just one
they watch and touch the organisms that live in
part of their job. They also are responsible for
the zoo. “I love to see people get excited about
providing interesting learning
experiences for
the thousands
of people of all
ages who visit
the zoo each
year. As educators, they train
and supervise
volunteer workers in the zoo.
They even
teach teachers
from schools
across the
United States
how to use
insects and
other museum
objects in their
classrooms.
Nathan and Faith are discussing the diet for the grasshopper that Faith is holding.
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COURTESY OF PEG KOETCH
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LESSON 20
THE KEY
TO
ORGANISMS—AN ASSESSMENT
the insects and other creatures we have here,”
says Faith. “As they do, I can see them become
relaxed and comfortable. What I want to do
most is turn the ‘yucks’ and ‘icks’ into more
‘wows’ and ‘ahhs.’”
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Collaboration Is Key
“One of our challenges,” says Nathan, “is to display the insects without stressing them and to
get them to breed in captivity.” With some
species, such as the milkweed bug, that’s easy.
COURTESY OF PEG KOETCH
A Busy, Buggy Job
“We maintain thousands of individual insects
just in our honeybee and ant colonies alone,”
says Nathan. “In fact, if you add up all the spiders, centipedes, millipedes, katydids, and the
rest, we probably care for more than almost
10,000 little organisms.” Can you imagine the
job of developing a dichotomous key for all
these organisms!
With the help of one assistant, Nathan and
Faith clean all the displays and feed all these
insects. Every week, they also stock up on
food supplies. They feed the herbivores yams,
lettuce, and apples, as well as leaves and
branches that are cut from special plants at a
nearby arboretum.
Food for the carnivores is delivered. “The
scorpions, spiders, and other carnivores eat
hundreds of crickets a week,” Nathan says.
“Every morning, I carefully inspect all the
displays,” Faith explains. “Insects have short
life spans, so it’s possible that during the night,
some of the animals may have died, hatched,
or molted.”
Nathan returns the grasshopper to its habitat while Faith looks on.
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LESSON 20
This tiny red-and-black bug, found throughout
the United States, thrives at the Insect Zoo.
Asian leaf insects, however, provide more of a
challenge. These insects, which look exactly
like the leaves of their treetop homes, thrive in
the hot, humid Asian forests. But at the Insect
Zoo, Asian leaf insects are finicky about their
food, temperature, and humidity requirements.
When they come up against a situation such as
this, Nathan and Faith do what any good scientists would do—ask questions, do library
research, get advice from other scientists, and
experiment, experiment, experiment.
“We call other entomologists to see how
they’re caring for their colonies,” Nathan
explains. “Then we experiment. For example,
we’ve altered the humidity and warmth of the
insects’ environment. We’ve added different oak
leaves to their diet. I have no doubt that eventually we’ll create the perfect habitat for Asian
leaf insects to molt, grow, and breed.”
“Success depends upon collaboration,” Faith
adds. “We call colleagues around the country
and around the world—and they call us. We
learn a lot from each other. By sharing information, we help each other find the best solutions
to problems.”
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Early Curiosity
As a child, Faith went on nature walks with her
dad, a science teacher. Together, they turned
over logs, picked up rocks, and “observed all
the small things everywhere.” Faith followed in
THE KEY
TO
ORGANISMS—AN ASSESSMENT
her dad’s footsteps and also became a science
teacher. After five years, she went to work as a
naturalist at an environmental center. That job
took her to the Monarch Butterfly wintering
grounds in the Mexican highlands. It was there,
surrounded by millions of Monarchs, that Faith
decided to become an entomologist.
“I love what I do!” declares Faith, sitting
below a butterfly mobile hanging in her office.
Just outside Nathan’s office is a large, bald-faced
hornets’ nest. “You only want to remove one of
these in late fall after all the hornets are gone,”
he cautions.
Nathan, too, developed an early interest in
small creatures. At age ten, he started to collect
butterflies. He went on to study entomology in
college and worked to help control gypsy moths
in Maryland forests before coming to the
Smithsonian Institution.
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Insect Ambassadors
Nathan and Faith make a great team. They’re full
of enthusiasm for their work, love sharing their
knowledge with museum visitors, and enjoy discussing their work with fellow scientists.
And, perhaps most important, they love
insects. “We are two of insects’ biggest fans,”
says Nathan. “And if you think about it, who
wouldn’t be? Over millions of years, insects
have become the world’s greatest success story.
So many different kinds have evolved over time
that insects flourish everywhere, from oceans to
rainforests, from deserts to our homes.” fi
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