Using Dichotomous Keys

1
Using Dichotomous Keys

• Mr. V. Perez
• Grade 6 Science

2
Field Guides

• If you found an organism that looked like a tick,
  how would you be able to determine its species?
• You could go to the library and look at a field
  guide
• Field guides contain descriptive words and/or
  photographs that are aids for identifying
  organisms
• Field guides have been created to find the
  scientific names of every organism including
  plants, fish, mushrooms, butterflies, etc.
• A dichotomous key is a detailed list of traits
  used to identify a specific organism

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Using Dichotomous Keys

• Dichotomous keys usually have two descriptive
  statements at each step (Ex 1a 1b, 2a 2b, 3a
  3b, etc)
• To use the key you must always answer a question
  at the first step, and then follow the other
  directions
• After each step of questions, there will be the
  name of a species, or directions to go to another
  step
• If you use the dichotomous key correctly, you
  will eventually wind up with the correct name for
  your species
• You could find the names of species from all over
  the world by (1) following the descriptions in
  the field guide, and (2) checking your
  identifications with a dichotomous key

4

• Start at 1a-1b Your tick is brown - Go to Step
  3
• Step 3a-3b Your tick is gt 0.5mm - Go to Step 4
• Step 4a-4b Your tick is brown with an oval,
  flattened body
• The dichotomous key classifies the tick as the
  Ornithodoros species

5
D
Size 1.5 cm