Beacon Lesson Plan Library
DescriptionStudents create dichotomous keys, classify items, and practice writing scientific names.
ObjectivesThe student knows that investigations are conducted to explore new phenomena, to check on previous results, to test how well a theory predicts, and to compare different theories.
Materials-Two bags of 15 bean soup
-One box of zippered plastic bags
-Note: Divide the beans from the two large bags of 15 bean soup into the smaller zippered plastic bags randomly-enough for each two students to have a bag.
Preparations1. Purchase zippered plastic bags and two bags of 15 bean soup.
2. Determine how many groups you will have and place a handful of beans in plastic bags, one bag of beans for each group.
Procedures1. Ask the class if they have heard of dichotomous keys.
2. Define each term and ask the class to take notes. Dichotomous means two equal parts. A key is something biologists use to identify organisms. A dichotomous key is a key that gives you the opportunity to make choices between alternative characteristics.
3. Explain to the class that when using a dichotomous key, first start with a large group of items and eventually work through to single items.
(See example in associated file.)
4. Separate the class into groups of two.
5. Give each group a small zippered plastic bag of beans of random assortment, prepared by the instuctor. Assign the task of creating a dichotomous key to identify the beans.
6. Instruct the students to sort the beans into smaller related groups until each of the beans that are identical are in their own group. Inform the class that you will be performing a demonstration for them and start by separating one of the zippered bags of beans into two groups, light beans and dark beans. Once those categories are decided, take those beans and separate them into two separate piles. Next you may separate the beans into beans with spots and beans without spots, etc. until you have separated the beans into their own individual groups, in which all the beans in that group are identical.
7. Once the demonstration is complete and each bean is in its own category, instruct the students that at this point they will need to assign that group of beans a scientific name. (A genus and species name.)
AssessmentsThis will be a formative assessment. The groups will be asked to switch dichotomous keys and try to identify each other's bag of beans in order to check the previous group's results. Some groups may have great difficulty if the first group did not do the key correctly. Formative feedback will occur as groups realize that checking results will sometimes show incorrect theories or actions. Once groups have had a chance to correct their keys or assess their original work, the groups will be asked to orally describe the way they conducted their explorations of the beans, checking the results, and reassessing their work. They must also explain how they arrived at the different classification categories of the beans orally.
ExtensionsYou can use a number of different objects for this exercise. It can also be done outdoors using plants.
Return to the Beacon Lesson Plan Library.