TOPIC 18: CLASSIFICATION

PART 2: DICHOTOMOUS KEYS

WHAT ARE DICHOTOMOUS KEYS??

  • A dichotomous key is a sequence of steps that allows one to identify a living organism.
  • The key will consist of a series of choices that lead the user to the correct name of the organism in question.
  • The term DIchotomous means that there will always be ______choices in each step of the key until the organism is correctly identified.
  • A dichotomous key consists of a series of two part statements that describe characteristics of organisms. At each step of a dichotomous key the user is presented with two choices. As the user makes a choice about a particular characteristic of an organism they are led to a new branch of the key.
  • Eventually the user will be led to the name of the organism that they are trying to identify!

FOLLOWING DICHOTOMOUS KEYS TO IDENTIFY UNKNOWN ORGANISMS

PRACTICE EXAMPLE:

Bird W = ______

Bird X = ______

Bird Y = ______

Bird Z = ______

CONSTRUCTING DICHOTOMOUS KEYS

  • You could be also be asked to construct a dichotomous key of your own.
  • When constructing a dichotomous key yourself, the first step is to look at the group of objects or organisms and separate them into TWO groupsbased on a SINGLE distinguishing characteristic.Then continue to separate each of the groups in the same way until each object has its own separate set of characteristics.
  • Some students find it easier to arrange their information into a spider key before setting it up in the traditional dichotomous key format.

EXAMPLE: CONSTRUCT A DICHOTOMOUS KEY FOR STATIONARY SUPPLIES

  • Lets look at an example and construct our own dichotomous key forstationary supplies taken from a student's pencil case!

Stationary Supplies to Categorize

STATIONARY KEY:

SAME INFORMATION PRESENTED THE WAY A TRADITIONAL DICHOTOMOUS KEY APPEARS:

1. a) ______...... ______

b)______...... ______

2. a)______...... ______

b) ______...... ______

3. a)______...... ______

b)______...... ______

4. a)______...... ______

b)______...... ______

5. a)______...... ______

b)______...... ______