Dichotomous Keys
Science: KS3, topic 1.6.2
Dichotomous Keys
Dichotomous keys help us classify organisms based on a series of observations of easily identifiable characteristics.
Making dichotomous keys
- Dichotomous keys are used to help classify organisms in an easy and effective way.
- Observations about the organisms are made about easily identifiable characteristics.
- These observations are made into questions.
The basis of dichotomous keys
- Di means two, so each questions has two parts (yes or no).
- Dichotomous keys can be a series of questions or a branching tree question set.
Examples of organisms in a dichotomous key
- Firstly, imagine the various organisms you may find on the seashore.
- Examples include:
- Bladder wrack Seaweed
- Herring Gull
- Shore Crab
- Sea Lettuce seaweed
- Anemone
An example dichotomous key (1)
- (1) Does it have wings?
- Yes – Herring Gull
- No – Question 2
- (2) Is it stuck to a rock?
- Yes- Anemone
- No – Question 3
- (3) Is it bright green?
- Yes – Sea lettuce seaweed
- No – Question 4
- (4) Does it have legs?
- Yes – Shore crab
- No – Bladder wrack seaweed
An example dichotomous key (1)
- (3) Is it bright green?
- Yes – Sea lettuce seaweed
- No – Question 4
- (4) Does it have legs?
- Yes – Shore crab
- No – Bladder wrack seaweed
Test yourself on Dichotomous Keys
What type of characteristics are used to build a dichotomous key?
What is the purpose of dichotomous keys?
An organism from the seashore has no wings but is stuck to a rock. Using the key, what is it?