WhatBelongsin Your 15-Bean Soup? - NSTA Learning Center

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
T E A C H I N G S T R A T E G I E S
What Belongs in Your
15-Bean Soup?
Using the Learning Cycle to
Address Misconceptions about
Construction of Taxonomic Keys
by Ann Ross and
Staria Vanderpool
Kidney beans, pinto beans, navy beans, pea beans, lima beans, black
beans, yellow lentils, green lentils, green split peas, cow peas—are
these all “beans”? Students can use seed characteristics to discriminate
between the different kinds of legumes using taxonomic classification
processes of sorting and ranking, followed by construction of taxonomic keys.
Classification involves two different stages in processing information: sorting
or grouping, and ranking. One example is the way we manage twin challenges
of laundry and getting dressed. On the front end, simply transferring laundry
from the dryer to a laundry basket is the fastest way to ensure that we have
clean clothes. It does not, however, reduce the complexity and time it takes to
dress in the morning. The next step is digging through the laundry baskets of
clothing in search of matching socks, unwrinkled tee shirts, or other essential
clothing items. (On average, dressing requires that you locate and coordinate
nine different items.)
An alternative strategy requires more time on the front end of the laundry
process, but reduces the amount of time spent per day. Clean laundry is sorted.
Socks are matched, underwear stacked, tee shirts folded, and jeans placed on
hangers. The final stage involves the classification process of ranking. Socks
and underwear are stored in separate drawers, tee shirts folded and stacked
together, and shirts, jeans, and outerwear hung in the closet. For the morning-challenged
person, getting dressed then requires locating the dresser, the
closet, and the shoe rack rather than tracking down nine individual items.
Many classification lesson plans instruct students to sort items from the
general to the specific. They continue to divide these groups into subgroups,
using a different characteristic each time, until only one specimen remains in
Ann Ross is an assistant professor of teacher education and Staria Vanderpool is an
assistant professor of botany at Arkansas State University in Jonesboro, Arkansas.
Nov/Dec 2004
science scope
23

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
T E A C H I N G S T R A T E G I E S
each group. Then they are instructed to devise and
test a dichotomous key. This is a standard approach
used in many classrooms. The value of this activity
is indicated by numerous and innovative techniques
for implementing hands-on classification activities
using jelly beans, cars, or potato chips, for example.
Standard classification activities lead to development
of skills such as observing, interpreting variability,
and sorting related objects into groups. However,
biological classification systems utilize two
separate information-processing stages—sorting and
ranking. Construction of keys that allow others to
discriminate the same groups is just one product of
biological taxonomy. The primary product is a classification
scheme that mirrors the biologist’s understanding
of the historical evolutionary relationships
among similar species. Standard classroom
activities that only involve sorting can lead to misconceptions
about biological classification of organisms
because they leap from sorting to naming,
omitting the ranking process.
A second misconception is that keys are derived
from a classification. Keys are logical devices constructed
by experts that allow others to easily identify
unknown objects. A key allows a user to match
an unknown object with its name, which is not a
function of the classification system. A classification
system reflects the degree of relatedness among the
included species.
One approach to teaching concepts and addressing
misconceptions is the Learning Cycle. The Learning
Cycle was introduced in the 1960s as an inquirybased
teaching technique consisting of three stages:
Exploration, Concept Introduction, and Application
(Beisenherz and Dantonio 1996). The Exploration
phase consists of unstructured, hands-on activities
leading to observations and data collection. The
teacher can identify misconceptions by listening carefully
as students explain their observations. In the
Concept Introduction stage, the scientific concept
that explains what students observed in the first stage
is introduced, including appropriate vocabulary. The
teacher may use textbooks or other materials to
present the concept. In the Application phase, students
pursue more focused
activities that reinforce or
extend basic concepts. The
Learning Cycle can be used
Explore classification at
www.scilinks.org.
Enter code SS110401.
to address some of the misconceptions
about biological
classification.
FIGURE 1
Secret sort, Exploration phase
Objective
Students will collect and sort materials gathered from their
environment.
Materials (per group of four students)
one shopping bag
two or three 100-cm lengths of yarn
three index cards
newspaper to cover table
small objects collected by students
Procedure
1. Divide students into groups of four and give each group a
shopping bag.
2. Explain to students that you want each group to collect as
many small objects lying on the ground as possible during a
15-minute walk in an assigned schoolyard area. The entire
collection should fit inside the shopping bag.
Safety note: Students should be cautioned to avoid
collecting live animals, animal droppings, broken glass,
or sharp objects. If poison ivy, poison oak, or poison
sumac are present in the collection area, students should be
shown which plants to avoid.
3. In the classroom, students spread newspapers over the
desktops, then sort their materials into separate piles, or
categories. They use the yarn to form loops to enclose groups
of items. Loops may be overlapped or objects placed outside
the loops. There is no right or wrong way to sort.
4. Secret sort: Ask each group to think of a word to describe
each category, write it down on an index card, and place the
card face down near the pile (for example: natural vs.
manmade, or living vs. nonliving).
5. Groups then take 10 minutes to move around the room and
guess how other groups sorted their objects.
6. To wrap up the Exploration phase, the teacher organizes a
table on the board with a column for each group. Hypotheses
made about criteria for grouping, as students move around
the room, are listed in rows for each student group. In the last
row, each group’s explanation of their secret sort is given.
7. Closure: The teacher explains that the basis of sorting,
such as the secret sort, is grouping two or more items that
have something in common. This process is fundamental
to classification.
8. Alternative collection options: Students may bring objects from
home, or the class may use materials collected by the teacher.
24 science scope Nov/Dec 2004

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
T E A C H I N G S T R A T E G I E S
FIGURE 2
Representative key for identification of dry edible beans available commercially.
Many of these are commonly found in 15-bean soup mix.
1a. Seed shape in side view round; hilum small, inconspicuous ............................................... Lentil (Lens culinaris)
1b. Seed shape in side view flattened; hilum large and conspicuous ......................................................................... 2
2a. Seed half-moon shaped; flattened in side view ..................................................................................................... 3
2b. Seed oval; rounded in side view ............................................................................................................................. 6
3a. Seed coat color solid ....................................................................................................................................... 4
3b. Seed coat variegated, base color splotched with contrasting color ............................................................... 5
4a. Seed large, length 19–25 mm; white ............................................... Large lima bean (Phaseolus lunata)
4b. Seed small, length 12–14 mm; green-white ............................................. Butterbean (Phaseolus lunata)
5a. Seed coat base color white, with purple blotches;
length 19–25 mm .................................................................. Large purple lima bean (Phaseolus lunata)
5b. Seed coat base color brown, with dark brown blotches;
length 12–15 mm ................................................................... Small brown lima bean (Phaseolus lunata)
6a. Seed coat color solid .............................................................................................................................................. 7
6b. Seed coat variegated, base color splotched with contrasting color .................................................................... 10
7a. Seed coat color white ............................................................................................................................................. 8
7b. Seed coat other colors ........................................................................................................................................... 9
8a. Seed kidney shaped; length 14–17 mm ........................................ Great Northern bean (Phaseolus vulgaris)
8b. Seed oval; length 7.5–11.5 mm ............................................................ Navy soup bean (Phaseolus vulgaris)
9a. Seed coat dark red; length 10–13 mm ............................................ Red soup bean (Phaseolus vulgaris)
9b. Seed coat black; length 8–11.5 mm ............................................. Black turtle bean (Phaseolus vulgaris)
10a. Seed coat base color white; reddish brown spot, restricted to region of hilum;
length 14–18 mm ............................................................................................... Soldier bean (Phaseolus vulgaris)
10b. Seed coat base color not white; spots various..................................................................................................... 11
11a. Base color dark brown; speckles tan, uniformly scattered across bean; length 12–14 mm;
seed coat shiny; shape slender and elongated ................................. Brown pinto bean (Phaseolus vulgaris)
11b. Base coat tan; variegations other colors, sizes, or distribution .................................................................... 12
12a. Variation pattern with streaks and speckles of purple/reddish purple ......... Cranberry bean (Phaseolus vulgaris)
12b. Variation pattern speckled only; brown speckles; seed coat dull;
shape rounded, chunky ......................................................................... Common pinto bean (Phaseolus vulgaris)
Exploration
In middle school science, students are introduced to the
concept of classification and the use of taxonomic keys.
One method of teaching classification is through the use
of the Learning Cycle. In the first or introductory phase,
Exploration, groups will use prior knowledge and observation
skills to sort materials collected during a walk around
the school yard, or that they or the teacher bring from
home. The “Secret Sort” game is used to explore differing
concepts of relatedness. This activity is adapted from “Session
1: Natural Collecting and Sorting” from the GEMS
book Investigating Artifacts (Barrett et al. 1992). Instructions
for this activity are given in Figure 1.
Concept introduction
During the second phase of the Learning Cycle, students
are introduced to concepts of sorting and ranking as part
of the process of classification. This phase will take two to
three class periods. The teacher relates the preceding lesson
to concepts of classification used by scientists. Through
Nov/Dec 2004
science scope
25

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
T E A C H I N G S T R A T E G I E S
various instructional methods, the
teacher explains that similarities
among biological groups result from
their evolutionary history and can be
understood by looking at similar and
dissimilar features of the organism.
The classification system is a standard
way to summarize current understanding
of relationships among
organisms. Each final category represents
a species.
For people, one of the most familiar
products of classification
processes is a taxonomic key that
allows them to identify a particular
species. As such, keys are derived
from classification systems
following the processes of sorting
and ranking. A good key allows the
user to identify unknown representatives
of a specific group. Figure 2
shows an example of a dichotomous
key devised by the authors for identification
of dry beans readily available
in supermarkets.
Dichotomous keys consist of a
series of paired statements (couplets).
Each statement allows the
user to divide a group into two
FIGURE 3
groups with contrasting features. Successive sets of
couplets allow the user to continue to separate items
in the group, until each separate object has been
placed in a unique category and named. Features to
evaluate when selecting, or preparing a key, include
the following:
• The key should focus on a defined region or group, for
example, “plants on campus,” or “frogs of Ohio.”
• It should be easy to follow, with indented or nested couplets.
• Each couplet should cleanly divide the group of items
into two distinct subgroups.
• Each successive set of couplets should then further subdivide
a subgroup into two distinct subgroups—until
eventually all the included items have been named.
• Empty couplets that do not serve to subdivide the pool
into two groups should not be included.
• Keys should be minimalist (minimum number of couplets,
characters, etc.) and short in style BUT they should also
be detailed and specific enough to be clear. Construction
of a useful key is a balance between excessive information
and adequate information.
Instructions for student key construction,
Application phase
Objective
Students will be able to group and rank paper fasteners as a basis for
constructing their own taxonomic keys.
Materials (per group of four students)
• assorted paper fasteners: various sizes, colors, materials, designs, etc. of
paper clips, push pins, thumbtacks, bulldog clips, staples, butterfly clips, brads,
and so on
• small plastic box to contain the fasteners
• ruler
• two or three 100-cm lengths of yarn
Procedure
1. Each group of students will receive a box of assorted paper fasteners.
2. Instruct the students to separate the fasteners and determine how many
different types they have (different species).
3. Students then place fasteners that are most similar to each other side by
side (different genera).
4. Students continue to group together similar objects until they have placed
all objects into one large group (kingdom of paper fasteners).
5. Students may find it helpful to use loops of yarn to contain their groups.
6. Using the rules for key construction, groups will then construct a written key
that would allow other groups of students to identify their species.
7. Groups can then exchange keys and test their usefulness.
Following explanation of concepts of classification and
key construction and use, students use the key in Figure 2 to
identify beans from a “15-bean soup mix” or a mixture of
beans provided by the teacher. Students will use the process
skills of observation, measuring, comparing and contrasting,
and inferring as they examine and identify beans in their
sample and learn how to use the key.
Application
In the application stage of the Learning Cycle students will
use their experience with dichotomous keys to test concepts
of biological classification by sorting, ranking, and writing
dichotomous keys for a group of related objects used to hold
papers together (Figure 3). Relatedness among the objects
varies based on the way they perform their function. This
allows the student groups to sort and rank based on degree
of relatedness among the materials. Features students may
use for classification include shape, color, material, mode of
action, or relative size.
Each group of students is given a mixed group of objects
commonly used to hold papers together. The number of items
available for this activity is extensive, inexpensive, and avail-
26 science scope Nov/Dec 2004

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
T E A C H I N G S T R A T E G I E S
FIGURE 4
FIGURE 5
Rubric for evaluating taxonomic keys
Able to identify items using the key
Key moves from general to specific
Couplets are indented or there is space between couplets
Quantitative, consistent measurements, not small, large
Precede with noun, followed by verb
Begin choices with same character
Begin couplet with different words
Couplets appropriate in length
Appropriate number of couplets
Use of appropriate vocabulary
Example of a key constructed
by students using communities
of paper fasteners
Comments on the key resulted from peer evaluation by
other student groups.
to enclose related groups—for example,
one loop of yarn could be used to enclose
each “species group,” with a second, larger
Yes No loop enclosing all species included in a
single genus. Once students have sorted
and ranked their groups, they should develop
a classification scheme that reflects
the relative degree of relationship among
the objects.
Once student groups have sorted
their paper fasteners, ranked them, and
developed a classification system, then
they can write a dichotomous key that
would allow other people to identify species
in their paper fastener community.
Evaluation of the keys may be done by
the teacher using a rubric such as that
shown in Figure 4. Alternatively, students
can exchange dichotomous keys and utilize peer evaluation
in a review and revision cycle prior to evaluation by
the instructor. Figure 5 shows peer review comments from
such a review and revision cycle, and indicates an extension
of this classroom activity into standard taxonomic names
assigned to the various paper fasteners.
Conclusion
The application of the Learning Cycle process to taxonomic
principles, hierarchical classification, and construction of
keys presents the components of classification that include
sorting (grouping) and ranking as separate stages in classification.
In addition, it separates production and use of keys
from the classification process and presents it as a useful product
of classification. Students frequently use keys to identify
trees, insects, wildflowers, minerals, or rocks. Understanding
concepts behind the classification process and production
of taxonomic keys will enable the students to select
appropriate keys for their region. A suggested extension is
for the student to find a key from a source such as the
Internet, libraries, bookstores, or state agencies to share with
other students in the class. ■
able from any office supply source. Students are instructed to
sort their paper fasteners into groups equivalent to species,
then rank groups into higher taxonomic categories (genus,
family, etc.). To aid in ranking, they may use yarn loops again
References
Barrett, K., et al. 1992. GEMS: Investigating artifacts. Berkeley, CA:
Lawrence Hall of Science, University of California at Berkeley.
Beisenherz, P. and M. Dantonio. 1996. Using the learning cycle to
teach physical science. Portsmouth, N.H.: Heinemann.
Berlin, B., D. E. Breedlove, and P. H. Raven. 1973. General principles
of classification and nomenclature in folk biology. American
Anthropologist 75: 214–42.
National Research Council (NRC). 1996. National Science Education
Standards. Washington, D.C.: National Academy Press.
Stuessy, T. F. 1990. Plant taxonomy. New York, N.Y.: Columbia
University Press.
Nov/Dec 2004
science scope
27