Name_______________________________________
Biology II --- January 2012
Making a Dichotomous Key --- Bacteria
Now that you’ve learned about some of the main characteristics of bacterial classification, you will
need to apply what you know. Your job is to make a dichotomous key to identify the 12 illustrated
bacteria on the last page.
Directions
1. Your first job is to outline the terms used to classify bacteria so you can use them in your
dichotomous key. The terms you will need to use fall in three categories: bacteria shape,
group arrangement, and flagella arrangement. Fill out the table below so you can use these
terms.
Shape
Description/illustration
Group Arrangement
Description/illustration
Flagella Arrangement
Description/illustration
1.
2.
3.
4.
1.
2.
3.
1.
2.
3.
4.
2. Now that you know what terms you’ll be using, apply them to the illustrated bacteria in the
chart on the last page. (Translation: use the terms to NAME THE BACTERIA!)
A.
G.
B.
H.
C.
I.
D.
J.
E.
K.
F.
L.
3. Now that you have your names, proceed by making a dichotomous key to identify the named
organisms. Use the terminology from the first page (e.g. bacteria shaped like a bacillus with
lophotrichous flagella arrangement) to differentiate between the illustrated bacteria. To do this,
you will need to apply terminology as well as your own imagination. Be creative! The
dichotomous key you come up with may be very different from the one your neighbor comes
up with…your key might be shorter or longer than others…there ISN’T ONE RIGHT WAY!
You can add or even subtract from the number of spaces I’ve provided you on the blank
dichotomous key on the next page.
4. IMPORTANT TIP: MAKE A DIAGRAM!!! Start by listing ALL bacteria (you can use just their
letters). Next, decide what characteristic (or decision) you’ll use to divide all listed organisms
into two groups. Use the following as an example to get you started:
Now that you have a “decision tree” that completely
outlines all bacteria and identifies them all, you can apply
A, B, F
the decision tree to your dichotomous key. Each decision
should represent a separate STEP in your key (in our
A, B, C, D, E, F
example, 1A would say “Have flagella” and 1B would say
“Don’t have flagella.” The direction for Step 1A would be
C,
D,
E
Don’t have flagella
“Go to 2,” while the instruction for 1B should be left blank
until you know what step to go to.
5. The best advice I can give is to just start working and to…
Have flagella
USE A PENCIL
.
1
A
B
2
A
B
3
A
B
4
A
B
5
A
B
6
A
B
7
A
B
8
A
B
Go to 2
A
B
B
C
D
E
F
G
H
I
J
K
L