Biology - M. Murphy
Dichotomous Key - Protists
In the previous lab, on bacterial identification, we used a flow chart to determine
the identity of unknown bacteria. In this lab, we'll use a similar tool, the
dichotomous key, to identify unknown protists.
To use a dichotomous key, always start with step #1 for every organism.
If we use the key above to identify organism A, we would go through the following steps:
1. Organism A does not have a shell, so the key tells us to go to step 3. Note, if we just skipped to
step 2 without reading where we were MEANT to go, we would mis-identify the animal. Always start
with step 1 for EVERY organism!
2. At step 3, our choices are legs are no legs. Since organism A does not have legs, we are to go to
3. At step 4, our choices are lives in water or on land. Since organism A lives in water, we find out
that it is a fish.
Go through the above key for organisms B and C. If you cannot determine the correct organism by
using the key, contact your instructor for help before going any further.
1a. Organism has a shell .... go to step 2
1b. Organism does not have a shell ... go to step 3
2a. Organism lives in water ... turtle
2b. Organism lives on land ... tortoise
3a. Organism has legs ... robin
3b. Organism does not have legs ... go to step 4
4a. Organism lives in water ... fish
4b. Organism lives on land ... snake
When you are confident in your ability to use the key to
identify organisms, begin the lab by clicking HERE.