Why Use Dichotomous Keys? Lesson
Objective: To develop classification skills, understand dichotomous keys, and understand a scientist’s
need for classification tools. Students will be able to understand the meaning of a “species,” a “family”
and an “order.” Students will be able to make their own simple dichotomous keys.
Materials: Printed and cut “specimen” pages
Hemiptera collection for viewing (or photos of Hemiptera)
Powerpoint presentation on non-intuitive animal classifications
NOS =
5. There is a level of creativity in science
6. Science has a subjective element
2. There is no single step-by-step method for doing science
K-12 Science and Engineering Practices Used in this lesson =
1. Asking questions and defining problems
2. Developing and using models
3. Planning and carrying out investigations
4. Analyzing and interpreting data
6. Constructing explanations and designing solutions
7. Engaging in written and oral argument from evidence
8. Obtaining, evaluating, and communicating information
8th grade Life Science Standards =
1. Reproduction is necessary for the continuation of every species.
2. Diversity of Species occurs through gradual processes over many generations. Fossil records
provide evidence that changes have occurred in number and types of species.
3. The characteristics of an organism are a result of inherited traits received from parent(s).
Context/ Planning Ahead:
- Print and cut out drawings of several superheros (6-8 per group)
- Print and cut out drawings of several insect species including a good number which will be difficult to
group correctly (for example: water scorpion, cicada, leafhopper, stinkbug, backswimmer, and wheel
bug which are all Hemiptera)
- Prepare a powerpoint with slides that show non-intuitive groupings (for example: eastern meadowlark
and western meadowlark, cheetah and puma and housecat vs. leopard, rove beetle and earwig, etc.)
Use this as an opportunity to define species according to the biological concept of species (contrast with
the morphological concept), then explain how taxonomy groups organisms and why it’s important to
scientists who want to study the life on this planet.
Misconceptions:
(taken from http://sciencenetlinks.com/lessons/identification-and-classification-ofgrassland-plants/)
Students often hold misconceptions about classification systems used in biology. Middle-school students
may believe that classification systems are natural, when they are in fact human-made systems that help
organize the diverse organisms found on earth (Benchmarks for Science Literacy, p.104.) or may have a
restricted understanding of the word "plant" and not understand that trees, vegetables, and grasses are
plants too. (Atlas of Science Literacy: Vol. 2, p.30.) It is important for teachers to pose questions to
students to bring forth misconceptions students may have about plants, identification, and classification.
Motivation/ Introduction:
1. Hand out the superhero cut-outs to groups and have them discuss how to organize the superheroes
into groups. They should then present to the class how they decided to group heroes and why. Have
them keep these groups in mind for later.
2. Hand out the insect cut-outs, and have students follow the same procedure but warn them that there
is a correct ordering which may not be easy to guess. Let them know that you do not expect anyone to
get everything right, but the point of the exercise is to see how scientists might approach real-life
organisms on the earth. Set it up so that they feel as though they were the first people to discover these
species and commissioned with the task of arranging them into groups.
Elaboration:
1. After the students present their decisions and reasoning for the insects, go through a description of
how the insects are actually related. Have an insect collection of Hemiptera for students to come and
observe. Give some time for observation and for questions.
2. Present the powerpoint, explaining why it’s difficult to use intuition to group species together. This is
why classification tools like dichotomous keys and field guides are so helpful.
3. Next, explain how a dichotomous key works and use it with the insect drawings that were handed out
in class.
4. Have the students write a dichotomous key for their superhero groupings. Make it clear that any
grouping can be valid if the reasoning is valid and matches with observations; what matters is that they
create something which makes sense and is usable.
5. Have groups switch tables leaving their dichotomous keys behind. They will go to another group’s
table while a group comes to their table. Each will see if they can follow the dichotomous key left behind
to determine the grouping of the superheroes. The visiting group will leave comments as to what was
helpful and what was hard to follow.
6. Finally, as a class we will discuss everything we did today and prepare the students for the lesson on
grassland plants tomorrow.
Assessment:
Each student will turn in their superhero keys along with the visiting group’s comments.
They will be graded on how clear they were and how they used scientific reasoning/ evidence and
observations and rationality to make their keys.
Possible variation – instead of grading the keys done in class, assign a homework where each student
creates a key for a group of non-living things which they can choose.
Extensions =
Information on creating a dichotomous key here =
http://www.docstoc.com/docs/19424227/Creating-A-Dichotomous-Key
Animal classification game here =
http://www.teachersdomain.org/resource/lsps07.sci.life.oate.animalclass/
Tree of life tool = http://sciencenetlinks.com/tools/the-tree-of-life/
Classification game tool = http://sciencenetlinks.com/tools/a-touch-of-class/
Bug bios pages = http://sciencenetlinks.com/tools/bug-bios/
Bugscope – very cool. Mail in insects and view them in a SEM microscope remotely.
http://bugscope.beckman.uiuc.edu/
Send pictures in for identification confirmation http://www.whatsthatbug.com/
Or http://www.bugguide.net/node/view/15740
Tree of life http://tolweb.org/tree/phylogeny.html
Online field guides - http://www.enature.com/home/
Follow-up Lesson (preferably the next day) =
A grassland plants activity found online = http://sciencenetlinks.com/lessons/identification-andclassification-of-grassland-plants/)
With grassland plant Dichotomous Keys found here =
http://ed.fnal.gov/data/life_sci/data/grasskey.html
If looking for grassland plants outside is not an option in your area, there is an online classroom version
here = http://ed.fnal.gov/data/life_sci/info/prairie_notes_ed.html
And http://ed.fnal.gov/data/life_sci/data/stud-index.shtml
Superhero Dichotomous Keys
Student Worksheet
1. If _____________________________________________________, then the superhero will be in
group one, which is………………………………………………………………….______________________________
If not, proceed to #2.
2. If ____________________________________________________, then the superhero will be in group
two, which is…………………………………………………………………………________________________________
If not, proceed to #3.
3. If ____________________________________________________, then the superhero will be in group
three, which is……………………………………………………………………….________________________________
If not, proceed to #4.
4. If ____________________________________________________, then the superhero will be in group
four, which is……………………………………………………………………….._________________________________
If not, then it is in group five, which is………………………………….__________________________________