Dichotomous Keys

1. Dichotomous Keys SBI3U

2. Dichotomous Key • 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, rocks, and fish.

3. 1 2 3 4 5 6 Dichotomous Keys • Dichotomous means "divided in two parts". • Each step has two choices; what you choose leads you to another question until the item is identified. • Based on physical characteristics.

4. Example of a dichotomous key… Dichotomous key

5. Dichotomous key • the dichotomous key can also be expressed in a diagrammatic form

6. Dichotomous Key Activity • Obtain 6 different shells and a bag. • Name your shells as a unique binomial species. • Create a dichotomous key that could be used to identify each species of shells. • Exchange your dichotomous key with another group in the class and use each other’s key to properly identify the species according to the other group’s assigned names. • Fill in the assessment sheet for the group whose key you are using and return it to them when finished.

7. 1 2 3 4 5 6 GROUP TASK • Each group gets ONE bag • Place 6 shells in the bag. • Make a Dichotomous key for ALL the items in the bag. • Follow procedures on the handout.

8. PROCEDURES • First make and answer key. • Write the names of your partners and bag # on your ANSWER key. • Assign a number to each object and make up a new name “scientific name” for each object. • Example: #1--------Mollusca minuta (small shell) • May want to trace an outline of the object • Make a dichotomous key for all objects in your bag.

9. Assessing the Effectiveness of Keys • Switch bags and keys with another group. • Use their key to identify their items. • Write the scientific name next to the object name. • Give them a level grade on their descriptions and accuracy of the items.