Classification Trees and
Dichotomous Keys 2
…yay…?
Dichotomous keys
• A dichotomous key is a series of
questions that have exactly two
answers
o Example: Does the shoe have laces or no laces?
o Example: Does the plant have seeds or no seeds?
o Non-example: What brand is the shoe? (has more than two answers)
• The answers must cover every possibility
o Example: Does the shoe have red on it or not?
o Example: Does the plant have flowers or no flowers?
o Non-example: Is the shoe red or black? (there are more possibilities than red
and black)
Dichotomous keys, continued
• Each time you answer a question it tells you where to go next
o Example: “If the shoe has Velcro, go to step 3”
• It is the same thing as a classification tree, but in text form
1. a. Feathers (go to 2)
b. No feathers (go to 3)
=
2. a. Swims……………………………………………………………Duck
b. Doesn’t swim……………………………………………….…Hen
3. a. Legs……………………………………………………………..Lizard
b. No legs………………………………………………………...Snake
Let’s use a key!
1a. Has 2 or 4 legs……………………………………….go to 2
1b. Does not have 2 or 4 legs………………………go to 3
As a group let’s try to do one.
2a. Does not have wings…….…………Canis familiaris
2b. Has wings …………………….……Passer domesticus
1a. Has 2 or 4 legs
1b. Doesn’t have 2 or 4 legs
3a. Only one cell…………………………………………go to 4
3b. Made of many cells………………………….……go to 5
3a. Organism is only one cell
3b. Organism has many cells
4a. Swims freely in water……………………Balantidium
4b. Stuck to the bottom………………………..……Stentor
4a. Organism swims in the water
4b. Organism is stuck to the ground
5a. Eats other things……………………………………go to 6
5b. Makes its own food…………………..………….go to 7
We have a
Balantidium!
6a. Lives in the ocean…………..Monodon monoceros
6b. Lives on land………………….Ophiophagus hannah
7a. Is a tree……………………………….. Pinus ponderosa
7b. Is an herb………………………...Taraxicum officinale
Let’s use a key!
1a. Has 2 or 4 legs……………………………………….go to 2
1b. Does not have 2 or 4 legs………………………go to 3
Now try it on your own.
2a. Does not have wings…….…………Canis familiaris
2b. Has wings …………………….……Passer domesticus
1a. Has 2 or 4 legs
1b. Doesn’t have 2 or 4 legs
3a. Only one cell…………………………………………go to 4
3b. Made of many cells………………………….……go to 5
3a. Organism is only one cell
3b. Organism has many cells
4a. Swims freely in water……………………Balantidium
4b. Stuck to the bottom………………………..……Stentor
5a. Organism has to eat
5b. Organism makes its own
food
5a. Eats other things……………………………………go to 6
5b. Makes its own food…………………..………….go to 7
7a. Organism is a tree
7b. Organism is an herb
We have Pinus ponderosa or
the ponderosa pine.
6a. Lives in the ocean…………..Monodon monoceros
6b. Lives on land………………….Ophiophagus hannah
7a. Is a tree……………………………….. Pinus ponderosa
7b. Is an herb………………………...Taraxicum officinale
Assignment:
1a. Has 2 or 4 legs……………………………………….go to 2
1b. Does not have 2 or 4 legs………………………go to 3
Use the key to figure out the organisms below.
Write your answers on a separate sheet of paper
from your notes (you will be turning this in).
2a. Does not have wings…….…………Canis familiaris
2b. Has wings …………………….……Passer domesticus
3a. Only one cell…………………………………………go to 4
3b. Made of many cells………………………….……go to 5
2.
1.
4a. Swims freely in water……………………Balantidium
4b. Stuck to the bottom………………………..……Stentor
6.
3.
5a. Eats other things……………………………………go to 6
5b. Makes its own food…………………..………….go to 7
6a. Lives in the ocean…………..Monodon monoceros
6b. Lives on land………………….Ophiophagus hannah
4.
5.
7a. Is a tree……………………………….. Pinus ponderosa
7b. Is an herb………………………...Taraxicum officinale
Assignment #2:
Use your shoe tree from yesterday to make your own key. You will be
turning this in as well.
1a. XXXXXX…………………………go to 2
1b. XXXXXX…………………...……go to 3
2a. XXXXXX…………………………..name
2b. XXXXXX…………………………..name
3a. XXXXXX………………………..…name
3b. XXXXXX………………………..…name