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

2. Dichotomous Keys
A dichotomous key = a system of identifying organisms using a two-choice key
a.k.a. Taxonomy key
"Dichotomous" means “divided into two parts” (Greek origin)
dichotomous keys always give two distinct choices in each step, often they are opposites
Black/white; good/evil; pointed/rounded

3. Virtual Dichotomous Key Activity

4. Two ways to write a dichotomous key:
Graphic Form
Written Form

5. Try this example:
EXPLORE: Introduce your students to the dichotomous key. Together, use the key to identify the group to which each organism belongs.
Assign the student reading. You may also wish to direct your students’ attention to the “Kingdoms” animation which is accessible from the multimedia lesson home page.

6. MAKING A DICHOTOMOUS CLASSIFICATION KEY

7. Making a Dichotomous Key

9. POSSIBLE “DERIVED CHARACTERISTICS/TRAITS”
Derived trait = a trait that the current organism has, & previous one didn't. For example:
Hammer-like head
All made of one material
Hinged
Has a sharp edge
Has holes

10. Hammer-like head
Other types of head

11. Hammer-like head
Other types of head

12. Hammer-like head Other types of head ALL Made of Wood
Made of Wood and other materials

13. Hammer-like head Other types of head Sides of head are different
Sides of head are same

14. Hammer-like head Other types of head Sides of head are different
Sides of head are same
All wooden
NOT all wooden

15. ? ? Hammer-like head Other types of head Sides of head are different
Sides of head are same ? ?
All wooden
Wooden and rubber

16. Things to consider when making a 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.
- Ex: “the body is round” vs “the body is square”