Classification is the KEY... Subject Areas: Science Setting: Classroom Duration: One to two class periods This lesson may be combined with Observations on the half shell Skills: observation, critical thinking, researching Vocabulary: taxonomy, classify, dichotomous key, scientific name, common name, organism, Kingdom, Phylum, Class, Order, Family, Genus, Species Correlation to Core Curriculum Standards: Science: 5.1 (A,B), 5.2 (A), 5.3 (A,C,D) 5.10 (A); Language Arts: 3.1 (E, H), 3.2 (A,B,C,D) Objectives: 1. Students will use observations to differentiate between items 2. Students will understand how objects are classified 3. Students will use dichotomous keys to classify organisms Materials: A variety of similar objects (balls), OR the shell board, or a collection of shells, pencil and paper or student journal Background: Everything can be classified, or put into categories based on similarities and differences. Scientists also classify living things to show how they are related, and how they are similar and different. This classification of living organisms is called taxonomy, and a scientist who does this is a taxonomist. A dichotomous key is used to classify organisms using a series of paired statements. Each set of statements highlights significant differences between the organisms to be classified. Through 8
process of elimination with each set of statements, an unknown organism can be identified based on its characteristics. In biology, we use Alpha taxonomy to classify all organisms. This system uses scientific names to identify living things, and put them in groups that share similarities. The groups are in a hierarchy, that is, they are nested inside each other. The following categories are used to classify animals in biology: Kingdom, Phylum, Class, Order, Family, Genus, and Species. The official classification of the Northern Quahog or hard clam is: Kingdom: Anamalia Phylum: Mollusca Class: Bivalvia Subclass: Lamellibranchiata Order: Heterodonta Family: Veneruidae Genus: Mercenaria Species: Mercenaria Procedure: Ask the students if they can think of examples where things are classified in their everyday lives (movies, music genres, clothes, sports equipment etc.) Ask students to think about sports equipment for a moment. How can sports equipment be divided up? Think of the difference between a hockey skate and a tennis ball - both are used in playing sports. This is one of many examples possible using everyday objects, and it is possible to bring in a variety of balls to use as an example classification and dichotomous key. Fruit would also be a good introductory example (apple, orange, grape, banana, strawberry, kiwi, etc.), but may be complicated by questions about seeds and structures. Others have used toys, shoes, dried beans, or students in the class. Regardless of which example you choose, have a variety of objects on hand for 9
students to describe and classify. This example uses different balls used in sports and games: soccer ball, football, tennis ball, golf ball, baseball, and basketball. Let the students tell you the difference between the different types of balls used to play sports. Try to get beyond overall shape and size, and talk about color, characteristic markings, or material from which they are made. Students may want to begin a journal to correspond with the lessons in this guide, and do all the exercises, drawings, and reflections in it. Procedure: Activity - Short Term/Younger Grades Make a dichotomous key together showing the differences between the types of balls. Each paired statement must be mutually exclusive! Multiple characteristics may be used in a pair, but the two sentences must be opposites for the key to work. The easiest way to do this is to have the B statement echo the A statement with the addition of the word not. Your key might look like this, although there are many possibilities: 1a. Ball is perfectly round go to 2. 1b. Ball is oblong football. 2a. Ball is larger than _(pick a useful number based on balls)_ cm..go to 3. 2b. Ball is smaller than cm. Go to 4. 3a. Ball is made of many angular panels sewn together soccer ball. 3b Ball is not made of angular panels sewn together.. basketball. 4a. Ball is fist size, with semicircular lines across it.. go to 5. 4b. Ball is not fist size with semicircular lines across it golf ball. 5a. Ball is very hard and covered in smooth material.baseball 5b. Ball is not very hard and not covered in smooth material.tennis ball. Ask students if they would be able to identify a golf ball using the key if they had never seen one before. Using the shell board and student journals (this will also be done in Observations on the Half Shell), have students make a list of the different characteristics of shellfish shells. 10
Which ones might differentiate between the different examples on the board? Emphasize that observing differences is the way scientists classify all living organisms. Procedure: Activity - In-Depth/Older Grades Have the students use the shells to write a dichotomous key, using observations they make about the shells different morphology. Have students draw their shells into a classification tree based on how similar or different they are. Example key 1a. Organism has one shell with a permanent opening go to 2. 1b. Organism has two shells that are hinged together go to 3. 2a. Shell long and loosely spiraled...whelk 2b. Shell squat and tightly coiled.moon snail. 3a. Organism has ridges that go across the shell short ways 4 3b. Organism has ridges that go across the shell long ways 5. Etc. Have students research other shellfish that are either not on the board or are not edible (razor clam, ribbed mussel, etc.) Have them include these organisms in their dichotomous keys. Extension: Taking it further Have students research the true classification of mollusks. What key characteristics besides shells are used by scientists to define shellfish species? Learn what characteristics make an oyster and a clam different from a mussel or from a whelk. Have them find and list the taxonomic classification of one shellfish species from Kingdom all the way down to scientific name (see previous example with hard clam). Alternately, have students put shellfish in a classification tree with a group of other organisms (fish, humans, dogs, etc.). 11
Assessment: Dichotomous keys Class Participation Classification Trees Worksheet 12