1. The document discusses dichotomous keys, which are tools that use a series of choices between two alternatives to identify organisms based on their characteristics. 2. A dichotomous key is divided into steps that present two choices, often opposites, to narrow down the identity of an organism. The user makes choices until reaching the organism's name. 3. The document provides an example of a dichotomous key that identifies creatures based on characteristics like wing position, number of antennae, and body shape. It also discusses best practices for constructing dichotomous keys.

1. Direct instruction:
Dichotomous Keys

2. Dichotomous key
1 With flower.
Without flower
Angiosperms
Go to 2
2 Seedless.
Seed bearing
Go to 3
Gymnosperms
3 Plant body do not differentiated into root,
stem and leaves.
Plant body differentiated into root, stem and
leaves
Go to 4
Go to 5
4 Without photosynthetic pigment.
With chlorophyll or other photosynthetic
pigment
Algae
Fungi
5 No vascular tissues.
With vascular tissues
Mosses
Fern
Another Example of a dichotomous key…

3. Life is organized at all levels
from cells to biosphere
how is life organizeD?how is life organizeD?

4. But what if we find things we
don't know and we want to know
what they are?
What’s my name !?
We use something’s
characteristics in a
similar way using…

5. 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” Greek origin
dichotomous keys always give two distinct
choices in each step, often they are opposites
Black/white; good/evil; pointed/rounded

6. How to use a dichotomous key?

7. Here are creatures we don’t know!
Lets choose one
How to use a Dichotomous Key?

8. Choose only one creature at a time.
How to use a Dichotomous Key?

9. Read steps 1a and 1b
Decide which statement is true
How to use a Dichotomous Key?
1b is true

10. Then follow the directions after that step.
Go to step 5!
How to use a Dichotomous Key?

11. At choice 5, you make another dichotomous choice
How to use a Dichotomous Key?
Go tostep 6!
5a is true

12. Keep going until you come to a step
that gives you the creature’s name.
C
How to use a Dichotomous Key?
6 a. The creature has one antennae Go to Step 7.

13. Choose a new creature and start at step 1a andstart at step 1a and
1b1b again. Continue until you find the creature’s
name.
C
How to use a Dichotomous Key?
Where do you start Again?

14. Then, find the names of all the creatures

15. 1. a. wings covered by an exoskeleton – go to step 2
b. wings freely observed – Go to step 3
2. a. body has a round shape ……….ladybug, a red beetle with
black spots
b. body has an elongated shape ……….grasshopper, a green
insect that hops
3. a. wings point out from the side of the body ……….dragonfly,
an insect that is 10- 15 cm long and lives in marshes
b. wings point to the posterior of the body ……….housefly, a
flying insect with red eyes and an annoying buzz

16. What if I needed to make 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.
- the body is “round” vs the body is “square”
- Finish the dichotomous key with a full description of the
organism

17. Dichotomous key
the dichotomous key can also be expressed in a diagram form
N o n - f lo w e r in g p l a n t s
W it h o u t p h o t s y n -
t h e t ic p i g m e n t
W it h c h l o r o p h y l l o r
o t h e r p h o t o s y n t h e t ic
p i g m e n t
A l g a e F u n g i
N o v a s c u la r
t is s u e s
W it h v a s c u l a r
t i s s u e s
M o s s e s G y m n o s p e r m s
P l a n t b o d y n o t
d i f f e r e n t ia t e d in t o
r o o t , s t e m a n d
le a v e s
P l a n t b o d y
d i f f e re n t ia t e d
in t o s t e m a n d
le a v e s
S e e d le s s S e e d - b e a r in g
F e r n s
F lo w e r in g P la n t s
( A n g io s p e r m )
W it h o u t f l o w e rW it h f l o w e r
P l a n t s