Zoology (080908 - 1 - Lab - Dichotomous Key - Bertie Bott Beans.wpd)
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Lab Activity - Classification
Making A Dichotomous Key
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Date -
You are an alien zoologist from a distant star system. You have been studying the various species you find on each
planet you visit. On this small, blue, planet you have rounded up a group of sample bipedal organisms and are amazed by
their diversity. You are convinced that every member of the group must actually be a separate species.... they all look so
DIFFERENT from one another!
Your zoologist partner, Blattzorg, says you are wrong. You realize that, in order to settle
this question, you are just going to have to divide your group up into sub-groups and devise a classification system.
To do this you must look for unique features that will let you isolate each INDIVIDUAL organism into a separate group.
Study the example (Figure 1). It shows how Harry and Ron divided up and classified the various colors of the jelly beans
found in a bag of Bertie Bott’s Every Flavor Beans. You will notice that, since every bean is the same size and shape,
Harry and Ron didn’t have a lot of options in making their “bean” key. They really had only three things that were different
among all of their beans.... color, spots and swirls.
Your job is to construct a similar Dichotomous (two branching) Key for the collection of specimens in your study group...
which just so happen to be all of the members of your own row plus the row NEXT to you (must total exactly 10 student
“specimens”)... yes, including YOU !!!
It’s up to you to decide HOW you are going to divide them up. Would COLOR work?
Well, unless you can accurately measure up to 10 different SHADES, color would probably not be the best criteria to use
as a grouping mechanism. I’d suggest that you begin by looking for a characteristic that will divide your large group, as
close as possible, into TWO, equal-sized groups... something pretty obvious.
You can then begin to sub-divide those two groups into smaller and smaller groups until you have the name of every person
in the room on their own line. Fortunately for you the members of your group probably display a lot greater variation than
Harry and Ron found among their beans. However, there IS one “gotcha” here.... you are trying to classify the individual
organisms here.... NOT their clothes!!
That’s right... your whole key would be trashed tomorrow if every one showed up
with different clothes on! It’s up to you to decide how “transient” a feature might be and whether it should be allowed. I’d
suggest that you all agree to allow any feature that is stuck to the organism... like fingernail polish or hair color. That does
not mean “stuck INTO” the organism... like ear rings.
Note: no feature may be used twice in your key.
Start by selecting that first, obvious, trait and placing it into two sentences.... “1A” and “1B”. This will be your first
“branch” (remember... “Dichotomous” means two branching).
1A - The organism is a male
1B - The organism is not a male
Something like...
Go to 2.
Notice that these are RIGHT justified.
Go to 15.
(Compare to Fig #1 on back)
As you can see you are going to be jumping around on your sheet as you try to construct your key. You will probably be
doing a lot of changing your mind.... so you will NOT want to use a pen for this activity. If all you have is a pen I’d suggest
that you build a “draft” key and then make your final copy after you have constructed your key far enough that you can see
the “big picture”.
Required Format:
Study the example “Beans” key on page #2. Notice that;
#1 it is in TW O columns.
Draw a line down the center of your sheet of COLLEGE-RULED paper.
#2 each pair of questions is separated by a blank line.
#3 each characteristic (question) has either a destination (Ex: “Go to 5") or a final identification name (Ex: “John Doe”)
Underline the final ID name (ex: “John Doe”) when you reach it.
Corrected by:
You may work in teams of TWO.
Verified by:
Good luck!