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A dichotomous key is a tool that scientists can use to identify an unknown organism or specimen.
Examples include… insects
The word dichotomous meansdivided in meansdivided in two parts.
Characteristics of a Dichotomous Key Dichotomous Key
Consists of a series of two part Consists of a series of two part statements that describe the characteristics of a specimen.
The user is presented The user is presented with two choices.
As the user makes a choice, they are led to a new branch of the key.
In the end, the user is led to the name of the specimen. In the end, the user is led to the name of the specimen.
Constructing a Dichotomous Key
Separate the Separate thespecimens into two groups based on one characteristic.
Example: A deck of playing cards could be separated into black cards and red cards.
Continue to separate the groups until each specimen has its own set of characteristics. Continue to separate the groups until each specimen has its own set of characteristics.
Example: Red cards can be separated into hearts / diamonds, then picture / number cards then male / female cards, etc.
Make the choice a positive one – for example, something is instead of is not.
Example: 2a.Black card is a spade…….4 2b.Black card is a club……….5 4a.Spade is a picture card…6 4b.Spade is a number card…7 6a.Picture card is male……….8 6b.Picture card is female…..9
Start both choices in a pair with the same word.Start both choices in a pair with the same word.
Example: 2a.Red card is a heart……….4 2b.Red card is a diamond……5
Start the next pairStart the next pair with different words.
Example: 2a.Red card is a heart……….4 2b.Red card is a diamond……5 4a.Heart is picture card…….6 4b.Heart is number card…….7 6a.Picture card is male……….8 6b.Picture card is female……9
There should be one less step than the total number of specimens to be identified.
* A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles,
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