How Scientists Classify Items 

 Introduction:

Classification involves the organization of items into groups according to common attributes.  It is an important part of the scientific process because it emphasizes the distinctions and relationships between different things.  Scientific concepts are often developed on the basis of facts or generalizations produced through classification.  The periodic table in chemistry classifies elements according to their physical properties.  In biology, the living world is classified into a variety of taxonomic categories on the basis of evolutionary relationships.  Classification is also a critical thinking skill that young children can use at a very early age.  Try asking a 4-year old to classify Beanie Babies into groups such as all the birds or even all the things that live in water or a jungle.  Once systems of classification are established, descriptive keys are useful guides to enable others to use the systems.  One particular type of key uses dichotomous divisions or categories that divide things into 2 discrete categories until each is distinguished.

National Standards Addressed:

The standard of Systems, order and organization belongs under the heading unifying concepts and organization.  This lesson allows students to develop their own classification skills in hopes that they will understand how scientists classify organisms.  The system of classification is rather straightforward and affords students the resources to better organize these organisms.

Inquiry and Constructivism is a teaching standard that would enable the students to set up their own system of classification and enable students to answer their own questions over why they chose to work the way that they did.

Objectives and Benchmarks:

This activity demonstrates a multiplicity of ways students can practice classification and develop the skill of devising systematic classification schemes including dichotomous keys.  Students will be able to classify objects by various features after completing this lesson. 

Materials:

Assorted collections of related objects

Advanced Preparation:

Assemble a collection of related objects- such as pop cans, pencils, stamps, tools, shells, beanie babies etc.

Hint: The more objects you have for each group the greater the challenge for students.

Procedure:

General Classification

Several collections of objects are displayed on tables in the classrooms.  Have students move around and handle the objects as much as they want.  Then they need to choose at least 5 collections and consider at least 3 distinctly different schemes they could use to classify the objects.

Questions:

Why did you classify the objects the way you did?

Compare your systems with those of other students.  Did you all classify the objects the same way?

Do you think scientists always classify things the same way or agree on systems of classification?

Dichotomous Keys

In the first exercise, the members of the class should be divided up by the instructor into a dichotomy or two mutually exclusive categories.  The students challenge is to figure out the distinction between the two groups each time.

In the second exercise, have each member of each table take off one of their shoes and place it on the table in the center of the group.  Each person should then develop their own dichotomous key or system of dual divisions.  First, students should observe the shoes to note similarities and differences.  Then they can choose a category that some of the shoes have and some do not. Have them write it down.  For each of those groups students can subdivide the shoes again into a category that describes some but not others.  Every time they divide a set of shoes, it should be into 2 groups. These divisions are based on some visible trait that some have and others do not.  They should continue dividing the shoes until there is only one in each category.  This is a dichotomous key.  They can test their key by tracing their other shoe through each of the descriptive categories to see if following the divisions leads them to match it with its mate. 

When they all have done this, they can compare the individual systems devised by people at their table and come to a group consensus as to the most creative and efficient scheme for a dichotomous key that classifies the shoes.   Have students map out this key on a blank sheet of paper.

Have students make another key covering one of the sets of Soda/Pop Cans.  They can just list the categories as they break it out, but they need to make sure each division is into a true dichotomy with two mutually exclusive categories.

Things to Consider:

Classification epitomizes the systematic aspect of a scientific process.  You should clearly understand the distinction between a general classification scheme and one that is dichotomous.

Possible Integration:

An English lesson could be integrated in by allowing the students to write about why they chose the classification system that they did.  

Critical Concepts: