dichotomous keys

1/19/23 Write Everything that is underlined in your journal and

Some text here about the topic of discussion

1/19/23 Using Dichotomous Keys

S: Instructions

DICHOTOMOUS KEY BASICS

1.USES ANATOMICAL FEATURES TO IDENTIFY ORGANISMS

2.TWO CHOICES AT EACH STEP OF THE KEY

3.WORK THROUGH EACH STEP ONE ORGANISM AT A TIME

UNTIL IDENTIFIED

4.ALWAYS START AT STEP 1

5.NEVER SKIP AHEAD

How is life organized?
Life is organized at all levels
from cells to biosphere

◦All Organisms and systems are
organized from simple parts
into complex systems that must
maintain homeostasis in order
to survive.

But what if we find things we
don't know and we want to
know what they are?

We use something’s characteristics in a similar
way using…

​Look at the video on the next slide and answer the questions that follow...

Open Ended

Type 4 things you learned from the video.

Dichotomous Keys

⚫A dichotomous key is a tool that allows the

user to determine the identity of items in the
natural world based on the items
characteristics.

⚫"Dichotomous" means divided into two parts.

⚫Dichotomous keys always give two distinct

choices in each step, often they are opposites.
⚫Black/white; good/evil; pointed/rounded

Here are creatures we don’t know!

Lets choose one

How to use a
Dichotomous Key?

How to use a
Dichotomous Key?

Choose only one creature at a time.

How to use a
Dichotomous Key?

• Read steps 1a and 1b

1a. The creature has two eyes.

Go to step 2.

1b. The creature has one eye. Go to step 5.

• Decide which statement is true.
•Statement 1b is true.

• Go to Step 5, skipping steps 2-4.

How to use a
Dichotomous Key?

• At 5, you make another dichotomous choice.
• Read steps 5a and 5b

5a. The creature has 1 or more antennae.

Go to step 6.

5b. The creature has no antennae. Its name is A.

• Decide which statement is true.
•Statement 5a is true.

• Go to Step 6.

Keep going until you come to a step that gives you the
creature’s name.

•Read steps 6a and 6b

6a. The creature has 1 antennae. Go to step 7.
6b. The creature has 2 antennae. Its name is C.

•Decide which statement is true.

•Statement 6b is true.

How to use a
Dichotomous Key?

• Choose a new creature and start at Step 1a and 1b

again.

• Continue until you find the creature’s name.
• Then find all the creature’s names.

How to use a
Dichotomous Key?

C

What if I need to Make
a Dichotomous Key:

• Use constant characteristics rather than variable ones.

(Flowers change with the seasons)

• Use measurements rather than terms like "large" and "small".

• Make the choice a positive one

• Something "is" instead of "is not".

• Ex: snake ears are internal only

• If possible, start both choices of a pair with the same

word or item.

• The body is “round” vs the body is “square”

• Finish the dichotomous key with a full description of the organism.

organism.

Dichotomous Keys

​This another way to write a

dichotomous key.

​Letter	​Name
​A	​Magnolia
​B	​
​C	​
​D	​
​E	​
​F	​
​G	​
​H	​

NOW…

​Get worksheets from the

substitute. Tomorrow you

have a reading in newsela.