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