A dichotomous key is a tool that scientists can use to identify an unknown organism or specimen

Dichotomous

Keys

Dichotomous

Keys

A dichotomous key is a tool

that scientists can use to identify an unknown

organism or specimen.

Dichotomous

Keys

Examples include…

insects

Dichotomous

Keys

trees

Dichotomous

Keys

rocks

Dichotomous

Keys

and shells.

Dichotomous

Keys

The word dichotomo

us means

“divided in two parts.”

Dichotomous

Keys

Characteristics of a

Dichotomous Key

Dichotomous

Keys

• Consists of a series of two

part statements

that describe the

characteristics of a specimen.

Dichotomous

Keys

Dichotomous

Keys

• The user is

presentedwith two choices.

Dichotomous

Keys

Dichotomous

Keys

As the user

makes a choice,

they are led to a

new branch of the key.

Dichotomous

Keys

Dichotomous

Keys

• In the end, the

user is led to the

name of the

specimen.

Dichotomous

Keys

Dichotomous

Keys

Constructing a

Dichotomous Key

Dichotomous

Keys

• Separate the

specimens into two groups

based on one

characteristic.

Dichotomous

Keys

Example:A deck of

playing cards could be

separated into black cards and red cards.

Dichotomous

Keys

• Continue to separate the groups until

each specimen has its own set of characteristic

s.

Dichotomous

Keys

Example:Red cards can be

separatedinto hearts /

diamonds, thenpicture / number

cards thenmale / female

cards, etc.

Dichotomous

Keys

Make the choice a

positive one –

for example, something

“is” instead of “is

not.”

Dichotomous

Keys

Example:2a.Black card is a spade…….42b.Black card is a club……….5

4a.Spade is a picture card…64b.Spade is a number card…7

6a.Picture card is male……….86b.Picture card is female…..9

Dichotomous

Keys

•Start both

choices in a pair

with the same word.

Dichotomous

Keys

Example:2a.Red card is a

heart……….42b.Red card is a diamond……5

Dichotomous

Keys

•Start the next pair

with different words.

Dichotomous

Keys

Example:2a.Red card is a heart……….42b.Red card is a diamond……5

4a.Heart is picture card…….64b.Heart is number card…….7

6a.Picture card is male……….86b.Picture card is female……9

Dichotomous

Keys

There should be one less

step than the total number

of specimens to

be identified.